For Maxi-Scooters The DarkSide (according to bandito2) Part 1 & 2

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For Maxi-Scooters The DarkSide (according to bandito2) Part 1 & 2

Post  bandito_two on Mon Nov 09, 2015 8:54 pm

After nearly  7 1/2 years of Darkside on Maxi-Scooters (250cc and larger twist & go motor scooters ... Not mopeds) I figured
I'd post what I know and think about the Darkside for the scooter riders. (and maybe even some "what I think I know" ) A lot
of it applies to motorcycles too, but mostly it is intended for the scooter crowd. (well, we're a crowd when there are enough
of us together all at one time.) Very Happy   It may not be perfect, but it is still pretty good IMO.

I split it into 2 parts so that it may be possibly less overwhelming since it is a pretty long post; it covers a lot though. So get
yourself comfortable, get your glasses  (if you need them) and have at it.

> "THE DARK SIDE" (according to bandito2)  
>  In defense of an unconventional idea
>>>>>>>>>>>---  PART ONE  ---<<<<<<<<<<<

The following here are many of my thoughts and opinions on the use of a passenger vehicle
tire (more commonly known as a car tire) on motorcycles & scooters. So from here on, when I
say car tire, I mean passenger vehicle tire and when I say bikes I pretty much mean
interchangeably motorcycles and/or scooters. I'll be specific when need be. This is intended
mostly for the benefit of riders of maxi-scooters (250cc and up) since some of those have
12, 13 & 14 inch rear rims that may be able to accept a car tire plus references and
examples to these scooters may be made from time to time. The concepts may also apply to
other bikes and tire/rim sizes as well.

Car tires getting mounted onto the REAR of a motorcycle/scooter is known as going "Dark
Side". Here in the USA/North America that is. Overseas, going "Dark Side" means going from
riding a scooter to riding a motorcycle. Apparently that is a Mods VS Rockers thing. We'll
just stick with the American version. "Dark Side" and "DarkSide" may be used interchangeably

This "Dark Side" piece will mostly be of my views and opinions, though those same views may
be shared by others. But it does contain a good amount of information and admittedly it
reflects my world view of car tire use on bikes. It will have well reasoned opinions,
personal experience, logical suppositions, anecdotal evidence and the like to support the
view. When I can find them, links to articles and items I refer to will be included for
anyone to go to and see for themselves for clarification and more information.

As it is with this subject matter, it would still likely not convince many naysayers. And
for those that do use a car tire, it will be like preaching to the choir. But They might
learn some things they didn't know about or even think of in that way and might gain a
better appreciation of going to the "Dark Side." Those readers would probably like it. And
for the uninformed, who are curious maybe, it could be a peek into the window of
understanding what all the fuss is about. And with the information presented, it may help
them with a decision if they had been considering whether or not to put a car tire on the
rear of their bike.

And for those that oppose the idea and practice, so as to not be completely biased, there
will be also be links to other articles and items that may be considered to be in opposition
of mounting a car tire onto a bike/rim. So there is info there to support their view, though
admittedly not much. I have briefly commented on some of those.

There will be times when information is repeated, sometimes in a different way. Many of the
points are brought up in different forums or the info has been repeated to make a point.
Sorry if that happens a lot, but removing some info from posts to avoid repeating something
and save space would make them time consuming to edit and would make the message appear
stunted and dry.

However, I must make the declaration that I am not a lawyer, scientist, designer, engineer,
nor physicist or magician. just a regular guy with a decent education and some outside of
the box ideas. But I don't need to know it all, I just need to know how to find the
information I want or need... And I know how to do that. And as a human, I am prone to the
human failings; errors, lapses of memory etc. Also I certainly can't be held responsible for
errors made by others in items in the provided links. So take it with a grain of salt and
draw your own conclusions. Then anything you do in regard to the information presented here
is completely your responsibility. This is all just to inform with what I have found and
what I think about it. So consider the risks, consider the benefits and do what you will.

A brief little spot of bike & car tire/rim history:
Long time ago when motorcycles were being improved upon, car tires were sometimes used on
both the front and rear of those bikes. It took a while for motorcycle tires to be more
specialized and commonly available. But once they were available, things pretty much stayed
that way because the bikes handled much better with the more rounded profile of motorcycle
specific tires. This is of course after motorcycles had been developed beyond the motorized
bicycle stage and bigger, heavier bikes meant a need for bigger heavier duty tires. Like
cars, quite a bit of development came as result of experimentation driven by the need for that is. And so bike tires and rims have been developed and standardized to
be very much as they are today because of racing and the demand made by an increasing number
of both motorcycles and cars. Tires and rims also then expanded off into specialized uses
and vehicles; cars, trucks, ATVs, flat track racing, off road, mud, sand, on road, drag
racing etc.

Car tires and motorcycle tires developed for everyday use commuting on modern roads is an
area of specialization that brings with them attributes of racing heritage. And so it is
with motorcycle tires that seem to wear out prematurely because of their round profiles that
history seems to be repeating itself a little. Now more people are putting car tires on the rear of
their bikes. The wider tread areas that were developed for cars using carcass components being
of radial design and having some better attributes than bias ply designs have shown to work well
on bikes. Those car tires are being used on the rear of their bikes in large part because of lower
rolling resistance, durability, endurance and because of their wide availability and sometimes lower
cost among other favorable attributes.

But these days, the modern car tire is applied almost exclusively only to the rear when dark
siding their bike. Motorcycle/scooter tires are still used on the front because bike
handling is much safer and easier to control with the rounded profile tire which facilitates
safe and smooth turning. A car tire with its more squared shoulder presents handling issues
which can be very problematic if used on the front; especially at speed. But if used on the
rear, it is certainly manageable and can be learned as easily and proficiently to control
as with standard bike tires.

That applies to a single track arrangement but is less critical on 2 & 3 track bikes like trikes
or on bikes with a side car where in most cases, the vehicle does not lean in turns and the
wheels remain perpendicular to the road very much like tires on a car. Then there are
instances of car tire use on all wheels, but only as long as it remains a non-leaning
multi-track vehicle. Interestingly however, there is one instance that I am aware of that a
tilting 3 wheel vehicle (Piaggio MP3 400) that uses car tires on all 3 wheels. The user
tells of a noted difference of "feel" citing a tendency to heavy steering, but seems
generally satisfied and accepting of the less than gracious handling but likes the idea of
tire longevity and less tire change frequency. Generally not recommended by the user as I
recall, but notes that it does work adequately and safely enough for him.

Though it seems slow to happen, R&D continues even today with development and introduction
of radial and dual compound tires for example. There has even been some experimentation with
segmented variable geometry tire and wheel combinations and other sorts of exotic tire and
rim materials and arrangements for cars like tires that are self sealing and self supporting
requiring no inflation; therefore immune to failure from puncture. Many are still too
complex to implement practically, but it is encouraging that research, development and
experimentation continues in the quest for better wheels and tires for cars and bikes.

A little bit about my story: (or - How I got into this mess)
It all started for me when I first saw a reverse trike called the T-REX. I entertained the
idea of taking a Honda Reflex scooter with a wrecked front end and converting it into a
trike a'la T-REX. That never came to fruition and I eventually abandoned the idea because of
not having the know-how to do the front end part. But I kept the rear wheel with the car
tire on it anyway and In June 2008 I put it on my Reflex scooter. It fits!! I was quite
pleased with how it worked for me. At first the handling felt different. Not better or
worse, just different. I think now the handling would feel different again if I were to go
back to using a scooter tire on the rear of my bikes.

I put 35,000 miles (and could have gone a few thousand more) using a 145/70R12 car tire and
changed it only because I wanted to try a taller tire. (155/80R12) I wanted to see what
effect it might have, if any at all on top speed and MPG. It required a modification to the
swingarm. Ultimately it is the wind resistance that limits top speed on the Reflex. So most
likely further use of that size tire will be for my Reflex streamliner project. And yes, the
engine RPMs were lower than what they were with the scooter tire at given speeds.

While searching the internet looking for info about a tire to fit the rim of the Reflex, I
came across several sites where they put car tires on their bikes.(It only works for the
rear wheel) One Dark Sider site only heard of one other scooter that was using a car tire...
A Burgman 650 they said, but I couldn't find it. Only about 6 months later did I ever find
another scooter Dark Sider. Then a while after using the car tire and telling others about
my experience, others began using one on their Reflex scooters as well. And later Honda Big
Ruckus riders and Yamaha Majesty 400 riders also began to follow my lead. All the while I
continued to find out more about DarkSiding since so many others were treating it as
sacrilege, bad mouthing me and what I was doing and putting out incorrect information. So I
found as much as I could to find the truth of things and to defend my view. Eventually I got
a Honda Silverwing and it too got a car tire put on the rear of it. Like many others that
have chosen to put a car tire on the rear of their bike, I will not be putting a bike tire
on the rear of any of my bikes again... except if one can not fit a car tire onto it or if
the bike is being sold/transferred to a new owner.

This is one of the first items on DarkSiding I ever read and made me want to find out more.

DarkSide Maxi-Scooter History: (What I have found so far)

(NOTE - This "maxi-scooter history" started out to be a message intended for the person that
first started using a car tire on his Yamaha Majesty 400 but then kind of morphed into the
following text covering the history of the beginnings of other Maxi-Scooters as well.)

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
I follow the DarkSide thing on scooters pretty closely and try to keep up on where and how
things have been progressing. I looked back at the hondareflexowners Yahoo group and found
your posts. Yes, all the messages are there from when it first started. In July of 2008, you
mentioned that you planned to put a Cooper classic (Mini?) tire on yours. I had already
Darksided my Reflex then but I am assuming you had DarkSided a different bike before then as
many other motorcyclists had done. In August of 2008 you acknowledge my "Pioneering" the
DarkSiding of the Reflex and I am rather pleased to see that you were the first to darkside
the Yamaha Majesty 400. I also found out that several of the Big Ruckus riders started to do
it after finding about it from the Reflex riders that I had enlightened with the DarkSide.

There were several of the bigger bikes Goldwings and others that were beginning to
popularize it more openly. But, the practice of "DarkSiding" had been done on the big bikes
for quite some time actually. On the scooters it has been somewhat more of a recent
development, though somebody once claimed they had seen a car tire on a Cushman  scooter
once  a long time ago. Maybe so, but it wasn't done regularly like it is being done these
days. And it may be that the tire on the Cushman only appeared to be an automobile tire. So,
as far as I have been able to find, here are the beginnings of Maxi-scooter darkside

June of 2006, a couple Youtube videos and some photobucket hosted pics were on the web as
the first verifiable incidence of a Darkside Maxi-scooter that I have been able to find;
specifically the Honda Silverwing 600... and it was done with air shocks for "Low Rider"
styling. Then more silence until August of 2008 when a member from the Yahoo
hondasilverwings group (w_hannon) recommended using a car tire as he was as a remedy to the
rough rear suspension to help give the bike a smoother ride. That caught the attention of a
lot of the Silverwing 600 riders and it took off from there.

Here are some pictures and videos of a "top secret" low rider Silverwing project of youtube
member smackykatt.

oh yeah, car tire on the rear.

And the short videos

On the forums, the first public mention of a DarkSide Silverwing was actually a request for
a car tire that would fit for a proposed 3 wheel car using a Silverwing 600 as the donor
vehicle back in November 2006. Didn't see any follow up on that.

Darksiding the Burgman scooters came out about December 2007; 6 months before I did my
Reflex. That is the earliest reference I can find anywhere so far that has somebody putting
a car tire on the rear of the Burgman in place of the bike tire. It was done by a member of
the BurgmanUSA site. (rimjaine) There was however, a mention of using car tires on trike
kitted Burgman scooters about a year earlier. But that was only for the kit outrigger wheels
being used. It wasn't clear if it was actually done then or even done to the rear wheel of
the scooter. It came with warnings not to ride the bike with the car tire without it being
with the trike kit, but who ever listens to such things anymore... it almost becomes an
invitation for someone to try and make it happen anyway. And so it did. But the practice
didn't really start to bloom until early 2008 when it became more popular. The Darkside
seems to be more popular as an acceptable modification to the Burgman 650 than it is with
the Honda Silverwing 600.

Of course then there was the entry of the Honda Reflex that I introduced in June 2008. The
Honda Big Ruckus didn't make Darkside entry until later on in October 2010 by a member from
the TotalRuckus site. (Moto Chimp) As of October 2015, I know of 36 Honda Reflex & Big
Ruckus riders that DarkSided their rides. There most likely are several more than that, but
those are the documented ones that I know of.

A later entry to the DarkSide practice was a Piaggio MP3 250 to its rear wheel in March of
2010 by a member from the Modern Vespa forum. (StickyFrog) He later sold the MP3 250 and got
a MP3 500 and DarkSided it too. Interestingly, another member from there, (rexkaru) put car
tires on the two front wheels of his MP3 400 in May 2012. He rode it like that for a while
and decided that since it was doing so well that he put a car tire on the rear in August.
Now all three wheels with car tires on make for a completely Darkside scooter. (the Darkside
is strong with this one)

Another late entry into the Darkside Maxi-scooter genre was the Yamaha Majesty 400 Darksided
by a member from the MajestyUSA forum (LCoop) in April 2011. He also owns a Reflex that he
had Darksided some time after July 2009. He still rides his DarkSide Majesty.

Nobody here in North America has Darksided a Honda Helix yet since 10" car tires are not
generally available at car tire shops because most cars in North America have larger wheels.
10 inch trailer tires might be easier to find but should not be used on bikes. (or cars)
Somewhere in the US somebody had a special 12" wheel made to fit a 12 inch tire onto a
Helix. It just barely fit and was a bike tire, but maybe that is indicative of the
possibility of a 10" car tire being able to fit. But it was a one off arrangement. There are
sources for 10" car tires here in the US, but nobody has taken the trouble to procure one
and try to fit one on yet.

Strangely or maybe not so strange is that I have found virtually zero DarkSide Chinese
scooters. Granted there are not many Chinese Maxi-Scooters that have gained any significant
poularity here in North America. That's not to say that it is not happening somewhere on
this planet, but if it is, then nobody is making mention of it. Plenty of 150cc class
Chinese scooters, but then those are not likely to be able to accept a car tire on the rear.

Other than the alleged Darkside Cushman and the low-rider Silverwing, as far as I can
discern, as a regular practice, I find myself at the very beginning of scooter Darksiding if
not one of the first few pioneers in the current trend.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Rubber compound hardness; Bike tire VS car tire:
Some people (the mis-informed) say that car tires last longer than motorcycle tires because
car tires have harder rubber. This is an incorrect assumption and is often repeated
misinformation. Even I thought that way at first until I found the truth of it. But after
being informed by those who knew better and further investigation of my own, I found that
indeed it is true. Tire rubber compound for cars IS typically softer than that of motorcycle
tires. I seem to recall reading that it is because car tire rubber compound has more
silicates which makes it softer and is there to help increase grip performance in cold and
wet conditions. Winter tires are even softer than all season or summer tires. But since
softer rubber wears faster and heat promotes wear, car winter tires are not going to last as
long as an all season or summer tire in high temperature environments. It will still out
last a bike tire by far. Only bike racing tires approach the softness of car tires and they
wear out much faster than standard duty bike tires that have a harder tire rubber compound.

There is a device called a Durometer which measures the hardness of materials and is used to
test tire compound hardness. Durometer testing proves that motorcycle tire compound is
typically harder than car tire compound. The Durometer hardness can even vary in some
motorcycle tires where some tires are made up of just one type/Durometer hardness of
compound and some motorcycle tires are made with differing hardnesses of compound across
their tread. Harder compound along the centerline of the tire for longevity for that part of
the tire and softer compound toward the outer edges of the tread for better grip in turns.
But still, it will typically show readings that indicate it to be harder than car tire
rubber compound. The exception may be with tires that are used for motorcycle racing. Those
tires use a compound which is softer than the rubber compound used with standard motorcycle
tires made for normal street use. Even so, some of those racing tires have harder rubber
than car tires.

BTW, a simple test a person can perform themself is to take a ball point pen (bic pen or
similar fixed nib type pen) and push the point into a bike tire tread and note how far it
goes in. Then do the same thing with the same amount of pressure into a car tire tread and
note the difference of how far it goes in when compared to the bike tire. (using a weight 2#
or so atop the pen for both tests would give a more consistent pressure and a magnifying
glass may help give a better view.) The nib going further in would indicate a softer
compound by comparison. While this is not a completely accurate test, it is very similar to
what a Durometer does when testing material hardness and should typically demonstrate a
difference in the rubber compound hardness/softness of car tires compared to MC/scooter
tires. To be fair, note that I say typically. That is because there may be instances where
the difference is too difficult to detect using this method and because some tire compounds
may differ by only a couple points. But, by and large, most results should confirm that
indeed, car tires do use a softer rubber than motorcycle tires.

Tire compound grip/coefficient of friction; Bike tire VS car tire:
People that say that motorcycle tire rubber grips better than car tire rubber because they
THINK bike tire rubber is a softer rubber and therefore grips better are NOT correct. They
are correct however, that generally, softer rubber has better adhesion than hard rubber.
Softer rubber has a higher co-efficient of friction than a harder rubber under the same load
and conditions. The softer rubber compound along with siping (the small slits in the tread)
of car tires conform better to small variations in the road surface and have a more
effective contact. Since car tire rubber compound IS typically softer than motorcycle tire
rubber compound, it would seem reasonable then to conclude that car tires would have better
traction than motorcycle tires. If softer compound = better traction and better traction =
safer, then one might conclude that a car tire is safer than a motorcycle tire; that is
coefficient of friction and traction wise at least.

By looking at the Standard Friction Equation, one can see that a softer rubber which can
have more surface contact down at microscopic levels is very likely to have a higher
coefficient of friction than a harder rubber bearing the same amount of load on the same
type and roughness of surface at the same temperatures. I would call the coefficient of
friction the "grip" factor. A higher number for coefficient of friction is better for our

However, as the information here points out, there may be differences due to other factors
like tread pattern as described in this part: (Coefficient when surfaces not hard and

Ultimately, this information is just a guide. The absolute truth to determining coefficient
of friction would need to be determined through testing. Even so, given a standard bike tire
and the car tire it replaces, using common sense and the information about coefficient of
friction, I would feel pretty confident with environmental and test surface conditions being
equal, that it would take more force to move and drag the car tire than it would the bike
tire. That would equate with better traction. And better traction is what is needed and
desired for better control.

Effect of Profile shape on tire longevity:
Again, often the wrong conclusion is drawn about tire longevity when comparing motorcycle
and car tires. Again, car tires do not have a harder rubber compound than bike tires, the
opposite is true. The durability of the softer compound car tires over bike tires comes in
part from the fact that the full width of the car tire tread is available and is used during
most of its life. That life being spent mostly upright and perpendicular to the road.

For the most part, the load and wear is distributed evenly across the full width of the
tread of a car tire and they would also tend to run cooler. So generally speaking, no single
area gets more wear than the rest. And the relatively light weight imposed upon that tire by
a scooter or motorcycle is far less than the weight that would bear down on it by a car. So
that part of the wear equation is lesser and equates to less wear than that which would be
generated by the much heavier weight of a car.

Typically, softer rubber does wear quicker than a harder rubber in an equal form factor and
load. But because the load is spread and shared across the full width of a car tire, it will
wear slower than a motorcycle tire imposed with the same load. It would also be reasonable
to infer then that if a motorcycle tire were made with a car tire rubber compound then that
tire would wear faster than a standard motorcycle tire of equal form factor under equal load
conditions. Indeed, racing tires for bikes have durometer numbers near that of car tires and
those racing tires do wear out rather faster compared to standard bike street tires and
street sport tires.

The motorcycle tire on the other hand, with its rounded profile can only use something
between 1/4 to 1/3 of its available tread width at any given time. Since a bike spends most
of its time upright, most of the load and wear is confined to that narrower section in the
middle of the tire. Localized pressure and friction induced heat on the center section tread
is conducive to quicker wear. Surely most have noticed when they need to change their rear
motorcycle/scooter tire that the center section is well worn but lots of unused tread
remains just off the center line on up to the sidewall. Motorcycle/scooter tire longevity is
largely limited by the durability of the center section tread of the tire. And since a bike
spends most of its time riding on that section of tire, it should come as no surprise then
that it wears out first even though the center section may be using a harder rubber than the
outer regions of the tread. IMO, a lot of good bike tire rubber is wasted from non-use.
(even by those that frequently ride the twisty roads)

A cursory measure of the 150/70-13 rear tire for my Silverwing FSC600A scooter shows a full
width of the tread contact face at about 7.5 inches. On the 165/65R13 car tire, the tread
contact face is about 5.125" across. So a bike tire actually has more tread face than a car
tire that may be used to replace it. But, In use, the bike tire can only use 1/4 to 1/3 of
that tread face width at any one time. So the bike tire at best is using just about 2.5
inches of that tread face width while the car tire is using the full 5.125" width. And since
the bike is typically upright most of the time, it follows naturally then that the 2.5 inch
wide center line of that bike rear tire wears away the most and sooner than the outer
sections which get less use. It wears there quicker even if it was a dual compound tire with
the harder, longer wearing center section. A little more about this can be found in PART 2,

This info here at this link, (from Dunlop motorcycle tires no less!) is lacking in its
explanation as to why motorcycle tires wear out so quickly compared to car tires. My
explanation is more informative and explains the effect of the differences in tread layout;
the Dunlop info doesn't do that.

Motorcycle tire manufacturers make the best tires they can for bikes and car tire
manufacturers make the best tires they can for cars. There is no conspiracy of motorcycle
tire manufacturers making tires that don't last just so that they can sell more bike tires
to a captive market. It is the rounded profile design of bike tires and the way they are
used that limits their usable lifetime. They could use an even harder tire compound to make
them last longer, but in doing so, they would have less grip. They could make a bike tire
that could last maybe near as long as a car tire and have it fit onto the bike rim as a
motorcycle tire would......... but it likely would look an awful lot like a car tire. (wide
center tread) And it would probably exhibit many of the same handling peculiarities of a car
tire on a bike. The rounded profile of a bike tire that makes it so smooth and consistent in
turns is the very thing that dooms it to a shorter life than a car tire.

About the contact patch:
It needs to be understood that the contact patch is determined by the load imposed upon a
tire and the air pressure in the tire and to some degree, the design structure of that tire.
Statically, the SIZE in surface area of the contact patch is most often a function of air
pressure and weight carried by the tire. But! the design of one tire may distribute the load
differently than another. The thing is, most tires do not spread the load uniformly across
the contact patch. Some parts of the contact patch bear more weight than others. The
distribution is going to be different on different tires. Even more dynamic changes happen
to the contact patch with the individual tires once it is in motion. How that distribution
is done is very often corporate intellectual property that the tire designers/manufacturers
are not just going to divulge for competitors to take advantage of.

I was not correct in my original assumptions that contact patch size is only a function of
vehicle weight and tire pressure. Tire width does indeed play a part, but is not a constant
or consistent indicator since aspect ratio also has a part along with sidewall deflection
and stiffness as well as other elements of a tire's construction. To determine that a wider
tire will always have a larger contact patch or that the contact patch size is always
dependent on vehicle weight and tire air pressure is not sufficient when comparing tires.
They only work as generalizations or loose rules of thumb. The only true way to tell with
accuracy is to actually measure. So, between differing tires at a given loaded weight and
tire air pressure, the contact patch may differ in shape and size to some degree. But the
general physics of loaded weight and air pressure still apply though possibly to differing
degrees between tires. Still, those differences are not going to be grossly exaggerated and
the contact patch size will still trend along weight/air pressure values.

More information can be found at this link and there are also links within this article that
are related. Granted, this deals with automobile application mostly, but some dynamics of a
rotating tire are common with motorcycle tires as well.

2 different tires of the same width at the same air pressure carrying the same amount of
weight can have differing contact patch sizes and shapes. This is possible because the
aspect ratios could be different, tire diameters could be different, tire carcass materials
and construction may be different, tread design differences may also affect the contact
patch pressure distribution. The contact patch pressure distribution is the thing that would
make for different sized contact patches on tires carrying the same amount of weight and
inflated to the same air pressure.

So many variables make absolute determinations difficult without actually measuring. Which,
for the average user is going to be impractical or near impossible. So "best estimations"
would have to be good enough for close enough. That is not exactly a situation that would
improve or degrade either side of the DarkSide argument. So my prior assertions that 2
different tires at the same air pressure and loaded weight will always have equally sized
contact patches is just as incorrect as the assertions of others that claim the wider tires
will always have a larger contact patch.

So what do we get from all of this?
#1) For any individual tire: Increase the loaded weight and/or reduce air pressure and the
contact patch will increase in size - Reduce the loaded weight and/or increase air pressure
and the contact patch will reduce in size. Those are laws of physics that will not change.

For a given loaded weight and tire air pressure when making comparisons:
#2) A wider tire will generally have a contact patch slightly larger than an equally loaded
narrower tire at the same air pressure.
#3) How the tires are constructed, rubber compound hardness, tire aspect ratio differences
and tire diameter differences can change what might be expected in contact patch size. Even
extremes in air pressure will exhibit differences in expected contact patch size.

Again, #1 applies always. - #2) applies most of the time, but the comparative size can
differ because of #3) and the only way to absolutely determine if one tire compared to
another is going to give a different contact patch size is to actually physically test and

Another thing that is different between car tires and motorcycle tires is the SHAPE of the
contact patch. With the bike upright, the car tire has a somewhat rectangular footprint
while a bike tire has a more oval shape to its footprint/contact patch. In a leaning turn,
the car tire has more of a half moon shape contact patch while the bike will still have an
oval shaped contact patch, though maybe slightly elongated. In a steep leaning turn the car
tire will have a more elongated & pointed shaped contact patch and the bike tire will have a
slightly elongated oval/half moon shaped contact patch.

This shape aspect is seldom discussed regarding DarkSiding and may actually be an area that
is more deserving of discussion than what it usually gets. The detractors of DarkSiding
often shout "danger, danger" and claim a razor thin edge of car tire in contact with the
road in a turn. (it is more of a cat's eye shape actually, not a razor thin line) However, I
am of the belief that the shape has less significance on traction than the size of a tire
contact patch because it is the contact SURFACE and coefficient of friction that determines
"GRIP" And "GRIP" is what it all is about for control in turns, acceleration, deceleration
and stopping. The contact patch is the interface between the vehicle and the road. The
traction of that interface is the most important thing in control regardless of the size or
shape the contact patch may have.

The sidewall:
Both the car tire tread and the sidewall can flex to allow tread to lie flat on the pavement
in a leaning turn. The tire does NOT ride on the sidewall. The sidewall is certainly strong
enough to handle what a scooter might demand of it; which is way less than what a car

The truth is that in most high speed turns, the road is banked and the tire remains closer
to being perpendicular to the road surface than one would find themselves on a flat curve. I
don't believe one could find a flat high speed curve; at least not for normal road use, only
for racing maybe.

A car will put tremendous loads on the sidewalls in turns. Car tires have to stay up and
keep the tire from just folding under, peeling off and having the car fall onto the rims but
still have the ability to flex. A bike can not even begin to approach those kind of forces
experienced by car tires as when used on a car; especially when a bike mostly directs force
DOWN to the tread and not as much across the width of the tire except while in turns. Even
so, it is not to the amounts that are developed by cars in turns.

Uneven road surfaces will often have one side of the tire carrying more of the the weight of
a car without failing. Even "curbing" a tire (running the sidewall up a curbside and
scrubbing the side wall) on occasion will not always cause immediate tire failure. A bike in
a steep turn rarely comes to the extreme end limit of the tire tread edge. Except racing
bikes maybe, but we're not talking racing or riding that extreme here. Riding extremely is
for the track using tires appropriate to the track.

Though one may find their self in an extreme situation, crashing or not has more to do with
rider skill than what kind of tire they have on the rear. If a bike ever manages to get up
onto the side wall of a car tire in a turn, it is probably because the bike has already
broken grip free of the road and scrubs the sidewall but only as it goes down. BTW, an
identical bike with a bike tire pressed into the same turn, exact same angle and speed would
likely be going down as well.

The sidewall and tread area does indeed flex on a car tire to allow the tread to remain in
contact. Even then, more of the weight is carried by one side of the tire, whereas the
sidewall on a bike tire is much more rigid and grip depends on the tread area toward the
edge of the bike tire and that tread area is much less flexible. Both tires basically do the
same job, just in different ways from each other. These aspects whether intentional or not
are a part of the design and function of the tires that allows each of them to work on

The tire/rim bead & inflation pressure:
Another thing that is different is the size and shape of the seating bead on the rims. There
are pictures of the difference between the two wheel types in a couple articles on the
subject of car tire use on bikes. My opinion on this is that yes, they are different and a
car tire does not seat onto a bike rim the same as it would on a car rim by virtue of the
differing bead layout and the very small difference in actual rim diameter at the bead. But,
by virtually all examples and experience of those that have used a car tire, it seats well
enough that there have not been any reports that I can ascertain of failure of the tire to
hold and keep air pressure because of that. If anything, the problem has been with getting
some car tires to seat on the bead on some bike rims. But this seems to be more common with
certain brands of tires mounted onto particular bike rims. And the tires are not coming off
of the rim in use either more often as some have wildly speculated. I have not heard nor
read of any cases of that, though I won't deny the possibility. But the same thing can be
said of some car tires on car rims and bike tires on bike rims as well. The usual reason a
tire may break loose from the tire bead is a loss of tire pressure. And that would affect
ANY tire on ANY rim.

Another area of concern for some is the notion that it takes excessive air pressure to get
the car tire bead to seat on the bike rim. It may be true some or a lot of the time, but not
always as can be seen in this youtube video nor always at the 100+ PSI as is sometimes

Some car tire onto car rim and bike tire onto bike rims do sometimes need a little bit of
persuasion to seat the bead with extra PSI too. Also, the maximum PSI indicated on a car
tire is the maximum PSI at its maximum load. The tire has no load on it at the time of
mounting to the bike rim and PSI gets reduced after it seats so the pressure over maximum is
short term. Even when on a bike, it is highly unlikely to be loaded near as high as when it
would be when mounted and used on a car. There are ways to get a car tire to seat on a bike
rim easier without excessive air pressure. (more than 2X tire max PSI) Rims that are clean,
smooth, nick free, have plenty of tire lube applied, ratchet strap used around center line
of a tire that is warmed are easier to get seated. Patience to wait for those things to work
and let the tire seat on its own at less than excessive, but more than maximum load PSI is a
better approach than using excessive over pressure at the outset.

As to setting the tire pressure, I would start with the the tire pressure about 6 to 8# over
the max pressure marked on the side of the tire as a starting point and will decrease
pressure 2 PSI at a time test riding between pressure changes until you can sense that it is
getting a dragging feeling or being squirmy. Then  bring the air pressure back up to a point
midway between the hi & lo settings and readjust the air pressure around that to the most
comfortable setting and maintain it there. Don't go any higher than 8 or 10 PSI above max
pressure. It won't do any more good beyond that and continuous over-pressure is not really
good for the tire and will promote uneven tire wear.

Concerns on camber thrust and camber angle:
A wikipedia item explains it pretty well. But it must be noted that even a leaning car tire
generates camber thrust. Even a straight sided coin leaned and rolling across a floor will
follow a curved track because of the force of camber thrust.

A thing to be noted though about riding a car tire toward the edge (but would more
accurately be called riding the tire at an "increased camber angle") is that tire heating
will occur because of the flexing tread & side wall. Not so good maybe for the big heavy
bikes, but would be less prevalent with smaller, lighter bikes like scooters. Also, that
happens with bike tires as well, but to a lesser degree because of their rounded profile.
That rounded profile provides a decrease in radius to the tire edge. Imagine a paper cup
rolling on its side. It naturally wants to turn around an arc. A car tire needs to form that
decreased radius by compressing sidewall and flexing tread imposed by the tires at an
increased camber angle. It gets the tire around the curve through all of that compressing
and flexing which generates heat. True enough, going straight ahead is not a problem. On big
bikes on hot days going through lots of twisty roads that put high demands on the sidewalls
should be of concern then to riders of those bikes; especially in tire heat generating kinds
of conditions. It should be much less of a concern to scooter riders because of the much
lighter weight and load imposed on the tire.

There is also something called "double dark side" And that means a bike with a car tire on
the rear and a motorcycle/scooter REAR tire mounted onto the front rim. Bike rear tires are
typically larger, taller sidewall section, wider and with deeper tread than a comparably
sized front tire. This practice is not as common as the usual dark side of using just a car
tire on the rear of ones bike. There is more to learn about this, so I will just give it the
little bit that I do know about it and my experience with it.

On my 2007 Reflex, I have gone double dark side. Generally I wouldn't recommend this for the
Reflex, but did it in part because I was using the bike to pull a single wheel trailer. The
slightly taller Silverwing 600 rear tire up front augmented the slightly taller car tire that
was being used on the rear. This combination was balanced and worked very well when pulling
the trailer. But it was not without issue when the trailer was not being used.

The wider tire had a tendency to "hunt". That is to say that it wanted to stay on the center
line of the tread much like the rear car tire wants the bike to stay upright and flat on the
tread. Though the scooter rear tire has a rounded profile, it is wider and less rounded than
a standard front tire. The bike would feel fidgety with both the front and rear trying to
keep lined up. No problem at all going straight ahead, but any turning would introduce the
very slight conflict. It was not unmanageable or serious enough to be a major concern, but
it was a little less than ideal. The steering would feel heavy with slow riding when it was
not pulling the trailer. When pulling the trailer naturally it felt heavier in general so
the steering heaviness was less noticeable.

I had an episode of pretty severe head shake once and thought the rear tire up front caused
it. But it turned out to be more an issue of slight misalignment, balance and air pressure
that was too low. After it was correctly adjusted, there were no further front wheel
wobble/head shake issues. The front fender required modification to accommodate the wider
rear tire as well.

From a message of mine from (edited)
I originated the use of a car tire on the Honda Reflex scooter and the use of a 150/70-13
scooter rear tire up on front of the Reflex for the "Double Dark Side" treatment. Some of
my comments on the subject of Dark Side can be found on the Yahoo hondareflexowners group
(as bandito_two) and on the (as bandito2) mostly in the "battle scooter"
sub-forum. There are other forums where I post, but these 2 are where most of my comments on
the Dark Side subject can be found. I consider them to be informative, logical, reasonable,
and worthwhile. I'm just a regular guy...with scooters... and (different) ideas. So, FWIW...

Being the pioneer type, I also run a Silverwing rear tire up front on my Honda Reflex
scooter. (rear tire up front along with car tire on the rear is known as DOUBLE DARK SIDE)
My bike had an episode of head shake once but that problem got resolved. It sticks like glue
to the road, barely shows any wear after several thousand miles of use and, well... it just
looks better too along with the taller car tire on the rear. Some big bikes do this too.

There are differing opinions as to which rotation direction to mount the rear tire up front.
I had mine mounted in the normal direction as the tread is designed to evacuate water best
in forward rotation. Remember even when mounted on the rear of a bike, that there are also
forces acting on that rear tire in braking which is in the opposite direction of forces from
acceleration. Even more so on a larger heavier bike, especially if it is heavily laden with
a passenger and extra gear.

The bike I have it mounted on is much smaller and lighter and I don't carry a passenger.
Still I don't think even that matters that much. On the rear, the forces work the tire in
both directions, on the front it is freewheeling and only gets force put to it when braking;
and that is mostly after the engine and rear wheel have already slowed the bike down. The
point is that the front tire does not get stressed as much as the rear tire. This becomes
evident if you stop and think about it; front tire even if slightly taller is narrower,
probably with tread not as deep as the rear yet typically lasts twice as long as the rear
tire which is much wider and usually has a deeper tread.

So, on the much larger, heavier bikes, mounting a rear tire up front in reverse rotation
makes sense to some of those guys. Then there are others who mount it in normal rotation for
many of the same reasons I did.

It did however, present an issue with the front fender. I rode it for a while without the
fender which was fine until encountering wet pavement. Then dirty water spray would be flung
up onto the windscreen, face shield, helmet, etc. making a mess of things and obscuring
vision. The fender was modified as a remedy.

This is all well and good for the Reflex, but I don't know how a larger tire (scooter rear
tire) would fit under the Silverwing front fender. In any event, the only rear tire that I
know of that >might< fit on the front of a Silverwing is a Pirelli Diablo 160/60-14. It
should have the same diameter as the standard 120/80-14 front tire so that exchange would
seem to pose no conflict as far as ABS operation goes when using a standard scooter rear
tire on the rear. But, a 160mm wide tire is a substantial 33% wider than the standard 120mm
wide front tire and may very well not be ideal at all handling wise.

Double Dark Side should not really be considered until after having experience with just the
car tire on the rear first. Having a car tire on the rear is one thing, it is a completely
different thing with a larger bike tire up front and brings with it a whole new set of
issues. Learn the peculiarities of the car tire first before moving on to the double Dark
Side if that is what one wants to try.

For the rear of the Silverwing, a 165/65R13 seems to be about as close to the standard
150/70-13 scooter rear tire as one can get with a car tire. The total difference in diameter
being only about 4.5mm taller with the car tire. Using this size car tire causes no problems
with the ABS functionality on the S-Wing. But because the speed sensor is at the rear wheel
the slightly taller car tire causes a slightly lower than actual mileage reading on the
odometer by a couple % IIRC. The speedometer reads just about right on per GPS comparison.

On my Reflex which has the speedometer operated from the front wheel, the once, usually
optimistic reading became a bit more accurate but at the expense of a slight error in the
odometer. That is with the Silverwing 600 scooter rear tire up front. So it now reads less than
actual. The Reflex speedometer and odometer are unaffected while using the standard scooter
tire up front. The Silverwing speedometer/odometer gets its info from the rear wheel. The
same thing does happen here as well, but only by a small amount. I once wondered if it would
still be enough change from standard to affect the ABS system. From experience I have found
that it does not. At least not with the 165/65R13 car tire on the ABS Silverwing nor with the
145/70R12 car tire on my Honda Reflex with ABS brakes.

I'm pretty sure, though not absolutely so for all bikes, that when the ABS detects error, it
defaults to standard mode. That is to say that the brakes would still work, but only just
like standard brakes would work. It does for my Silverwing. I had mounted a 175/70R13 tire
on a rear rim that didn't have the ABS pulser ring. The ABS never got past the initial start
up test so the ABS was not active, but did not give an error warning. The brakes worked as
standard brakes and I could get the rear tire to skid in hard braking. If technical types
here know for sure about how it might affect ABS on other bikes, it would be greatly
appreciated if it were clarified for us.

I just recently got my Silverwing up and running after just over 3 1/2 years of it being a
dirty, dusty and damaged garage queen. The Silverwing is Dark Side now with a 165/65R13 car
tire which is the closest to the standard 150/70-13 scooter rear tire diameter wise as far
as car tires go. It has no negative effect on the ABS braking system which works normally as
it should. (Dark Sided, but not double Dark Side)

Last edited by bandito_two on Thu Jul 14, 2016 10:32 am; edited 9 times in total

Number of posts : 43
Location : Rochester Hills, Michigan
Registration date : 2008-07-11

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Re: For Maxi-Scooters The DarkSide (according to bandito2) Part 1 & 2

Post  bandito_two on Mon Nov 09, 2015 9:34 pm

> "THE DARK SIDE" (according to bandito2)  
>  In defense of an unconventional idea
>>>>>>>>>>>---  PART TWO  ---<<<<<<<<<<<

Some things are about equally as bad/good:
Often as it is with many things, you get what you pay for. Some more costly bike tires are
of better quality than others and becomes evident during use. Same thing with car tires.
(used on a car or bike) Generally speaking that is. Some do have personal preferences for
their intended use regardless of the cost or advertised quality.

One of the bigger WORRIES would be tire pressure loss & deflation while riding and
the relative flexibility of the sidewall of a car tire compared to the typically stiffer
sidewall of a bike tire and the handling problems that can pose. At partial deflation, both
make the bike feel heavy, squirmy, noisy more difficult to control, heat the tires
excessively and tires wear faster.

Run-flat tires that some of the big cruisers use mitigate that problem to a better degree so
that a loss of tire pressure is not as likely to end catastrophically. I am not aware of
run-flat tires available in sizes that would fit on scooters. I'm not saying they don't
exist, it's just that I've not seen any... For the Honda Reflex size tire at any rate though
it may be more likely for the Silverwing 600. Typically with bike tires, the sidewall is
fairly stiff and it can be difficult to tell that the tire air pressure is low when the
sidewall of the tire doesn't bulge out like it would with a typical car tire. But I do seem
to vaguely recall where the sidewall on run flat tires for cars do not do the usual bulge
and the way to be absolutely certain the tire pressure is correct is to do a check of the
tire PSI. I would suspect too that the stiffer bike tire sidewall would be about equal at
levering the tire off of the bead as the rim sliding across the sidewall of a car tire at
full deflation while in motion. With the exception of run-flat tires perhaps, both are going
to be dangerous and difficult to manage at full deflation while in motion.

Car tire rubber IS softer than bike tire compound. So if softer means stickier/better grip
and better grip means safer then one may conclude that car tires grip better than motorcycle
tires and are safer because of that. That could be determined by accurate testing. I would
think that based on coefficient of friction alone that generally car tires would have better
grip. And certainly a softer rubber is going to grip better in wet conditions. However,
Winter/snow tires have an even softer rubber compound but are really best suited for use in
temperatures of 7°C = 44.6°F and less. Too soft really for warm weather use ... they will
wear faster and not grip as well as an all season tire.

Mmm BEEFY, but looks are subjective and really a matter of personal preference.

The thing about wear is that a car tire shares the load and wear across the full width of
the tread face almost all the time whereas a bike tire with its arced tread profile can only
use about 1/3 to 1/4 of its tread face at any one given time. And since bikes typically ride
most of the time upright, it is no wonder then that the center-line of the bike tread wears
down the most... and first... and faster than a car tire; even though the bike tire has a
harder rubber compound along that center-line and the car tire with its softer compound. It
is the arc profile of the bike tire that makes it so smooth and consistent in turns, but is
also the main reason why they wear out so much faster than car tires. Tire diameter plays a
part in this as well; which brings me to another way to explain tread use...

My Silverwing scooter tire is just a little over 21" in diameter. So that X Pi = about 66.5"
circumference. Then that, X 2.125" of tire width touching the road = about 141.4 square
inches of tread face that makes contact with the road in one tire revolution.

Using the car tire which has a diameter of about 22.44" has a circumference of about 70.5".
That, X the 5.125"  tread width on the ground = just over 361 square inches of tread face
that makes contact with the road in one tire revolution. Or put another way; the bike tire
does all that work on that 2.125" wide area and the car tire gets it spread out over an area
about 2.55 X as large in one revolution of the wheel. So just by that, it is not hard to
imagine why a car tire seems to last at least something over 2 1/2 times as long as a bike
tire. And often lasts much longer than that.

For example; I used a 145/70R13 on my Honda Reflex scooter that got used for 35K miles. It
could have gone a few thousand miles more but I changed it so I could try out an even taller
car tire. Rear scooter tire on the Reflex normally lasts about 6K miles on average. A car
tire lasted about 5 to 6 times as long in my application. Different tires may last more or
less than that, but in any event, certainly multiple times longer than a standard bike tire.

Usually, initial vehicle acceleration rate is less by cars than bikes because of the car's
weight and general lack of comparable HP/weight ratio to get it moving. Bikes can do this
almost without really trying because of their lighter weight. This makes for a higher HP to
weight ratio for many bikes. Bike tires are designed and built to withstand the acceleration
demands of bikes. But they will still wear out rather quickly when compared to car tires
partly because of that. But car tires are also built to endure acceleration and deceleration
by much heavier vehicles. That demand is much lower when used on the much lighter motorcycle
or scooter. That lower demand would equate with an even lower wear rate for the car tire
than a motorcycle tire when used in normal commuting on a bike.

Scooters are far lighter, go slower in general and are far less demanding on car tires than
cars. For example, the 145/70R12 Federal SS-657 tire that I used has a speed rating T = 118
mph and the scooter barely can make it past 80mph. Load rating for the car tire is 69 which
means 717 pounds max. The scooter weighs about 375 plus whatever the rider/passenger/gear
weighs and only about half that weight is carried by the rear wheel.

The standard Bridgestone HOOP scooter tire has a load rating of 62 = 584 pounds max and a
speed rating L = 75mph. No way that the scooter could even get close to imposing the levels
of stress like those that can be developed by a car in normal use. Plus, I think car tires
on a scooter are less prone to puncture. I could be wrong about that, but I doubt it. It is
clear that speed and load ratings of the car tire far exceed the specifications for the
scooter tire.

Many of the usable car tires cost near the same if not less than maxi-scooter tires. Cost
savings come in some part from not needing to change rear tires as often as a standard rear
tire. Not just in cost for the tire itself, but also for the installation of those tires
onto the rims. Except that is, if one does their own tire mounting and don't need to pay a
shop to do it for them.

As stated above; They don't need to be changed as often because car tires will last longer
than scooter tires. Tire changes may actually end up needing to be done because of tire age
rather than wear. That is unless one puts enough mileage on it before the recommended 6 year
tire age limit.

A tire that is taller than stock will act to raise the effective drive ratio = lower engine
RPM = less fuel used and would actually have less rolling resistance in use than a standard
scooter/motorcycle tire.

Another thing with a taller tire is that rolling resistance is less because of that load and
tread distribution and because of the mechanical advantage that typically larger diameter of
car tires have compared to bike tires. Think 2 wheelbarrows with same width wheels but one
taller than the other. With a good, but equal amount of weight loaded push them through the
dirt. Ah Ha! you noticed that all things being equal but the diameter that it was easier to
push the wheelbarrow with the taller wheel. AND!! it is even much easier if the taller tire
is also wider. (like car tires are when compared to bike tires)  See?

Many claim better braking. There is no published data from unbiased scientific testing to my
knowledge that either confirms or disproves the claims. Mostly the claims are supported only
by user anecdotes.

As above, but I'll add to that. Initially I had concerns that hydroplaning may be a problem
with the wider tire. But in my experience found the car tire to be better at evacuating
water than the scooter tire which had begun to hydroplane on occasion. The thing that makes
me think car tires work better in the wet is that though the tread facing the road is wider,
it also has many more channels for the water to get moved through. The bike tire, though  
narrower frontally than a car tire, projects a more unified, less blocky surface. So once
the water starts lifting the tire, it only needs to get that one surface started, then the
whole thing starts to plane. The car tire would seem to take more to get all of the surfaces
to lift since there are more channels for water to slip by. Also the tire compund in car
tires is made to have better grip in cold and wet conditions.

Almost goes without saying about speed ratings since cars are much heavier and can typically
go faster than scooters. Some car tires that fit the Reflex are rated for full gross load
near 700#. The Reflex weighs about 375# with roughly half that weight carried on the rear.
Ditto for anything else on the bike. Rider, gear, etc. Load and speed characteristics will
apply in similar fashion to bigger maxi-scooters that use bigger tires with their
correspondingly higher speed and load ratings.

It has been my experience that car tire works better with less squirming on sand and gravel,
but YMMV

Many state no problems riding hard in the twisties and doing so with confidence. I have done
so myself. A competent and able rider should have no problems or very few anyway, adapting
to the different feel and manner which a car tire behaves in all riding modes. Not better or
worse really, but definitely different. Yes, it IS different, but it is not difficult to
adapt to and get comfortable and confident with.


The subtle difference in size of car rims VS bike rims can cause fitment problems when
mounting a car tire onto a bike rim as well as the differing bead of a car tire to the bead
seat of the bike rim.

Some have had difficulty getting a car tire to seat on the rim bead, ruined tires in the
attempt or have scratched rims getting difficult tires mounted. This problem can be reduced
some by having the rim clean and nick free. It also helps if the tire is warmed up a bit
first along with using plenty of tire mounting lubricant. Other methods to help mount car
tires involve the use of a ratchet strap around the circumference of the tire. Again, some
have had these same types of problems with standard bike tires. Also it may be noted that
some car tires being mounted onto car rims aren't immune to this type of problem as well. It
sometimes requires what some would describe as use of excessive pressure to seat the bead of
the car tire onto the bike rim. This is probably one of the two preeminent concerns of those
opposed to the practice of Dark Siding. The other concern they have is with tire grip. But
they are mistaken about that assumption as car tire compound is softer with a better grip
than the harder bike tire compound.

Some may find it difficult to find a car tire that would fit on their bike and mount easily
and successfully onto its rim. A person also may have trouble finding a car tire readily
available in a style or brand of their liking or at a price that they are willing to pay.
(but these points could also be just as true for a bike tire as well)

Some establishments may refuse to mount a car tire onto a bike. They may have their reasons
for refusing, but many places will do the job without question.

Some may feel hesitant and anxious due to the fear mongering promulgated by those opposed to
using car tires on bikes. Very nearly all that oppose the practice have no experience at all
whatsoever with car tire use and base their beliefs on theory, misinformation, paranoia,  
misunderstanding, or are merely repeating things they have read or heard without having
investigated the validity of those claims.

Slightly slower acceleration if the tire is taller than the standard bike tire. (mostly
apparent, if at all from a standing start; but less so once under way.)

Similarly, roads with differing surface heights require more rider attention. Surface height
changes occurring in steps like new road surfacing added atop old for instance may make the
bike feel like it is hopping or squirming off one onto the other rather than rolling on or
off. Some have commented on notchy stepping and squirm on rough ridged and uneven pavement
and on steel grating like that experienced on some bridges. I don't believe there is much
danger in that but it may be an uncomfortable sensation for some riders. This may also occur
with bike tires as well but to a lesser degree because the rounded profile tire will tend to
"roll up" onto uneven pavement smoother than a more squared shoulder of a car tire.

With crowned roads, the car tire will make a bike have a tendency to want to move down the
crown. Initially, these control issues may be of concern but eventually can become better
understood/learned/accounted for, adapted and adjusted for and accepted.... yes, one can
learn and adapt if they are willing to accept the differences.

Initially, some don't like the difference in how it feels in turns. Car tires seem to have a
tendency to want to keep the bike upright and requires more input during turns. With a car
tire, one needs to "hold" it in a turn with more active counter steer. Relax the control and
it will start to come off the turn. And, though not documented specifically, with the
tendency of the tire to make the bike want to stand up, it may make the bike seem more
susceptible to "high siding". (that is merely conjecture on my part, but seems logical) Like
anything else that is different than the usual, different techniques need to be employed. In
turns the sidewall compresses and the tread flexes and the tire tends to resist that and ...
well, it does have a tendency to want to "stand up" because it is the tire that is trying to
equalize the tension/compression of the sidewall on each side of the tire and to get back up
onto the flatter, more dynamically stable tread area of the tire.

How a car tire makes a bike feel when riding is not much unlike what one may experience from
the "squared off" tire profile from a well worn bike tire. Some may just not care for the
idea of riding with that aspect present all the time. The issue of the "squared shoulders"
of a car tire has more to do with getting acclimated to the different "feel" and handling
attributes than being a safety issue. If one can't or won't learn and adapt, then they
probably shouldn't be riding motorbikes at all; car tires or not. But like so many other
things, they can learn it and adjust their riding style accordingly until controlling it
becomes natural and second nature. Happens all the time. Just like they do with their bike
as the tire gradually wears. They don't even have to think about it too much; (consciously)
they just ride. Still, some don't like the "transition" of resistance going from upright to
leaning into a turn.

However, some car tires with taller sidewall aspect ratios tend to be slightly more rounded
at the shoulder and seem to exhibit less turn resistance. This gives a more comfortable and
more familiar feel to the ride than lower aspect ratio, lower profile car tires.

Some may worry about the potential for litigation or denial of insurance coverage in the
event of an accident/incident involving a bike while using a car tire. (I've never heard of
any instances of that happening, but there is a remote possibility that it has.) And I have
not found DMV law (in Michigan anyway) that precludes a motorcycle/scooter from using a car
tire or that requires only MC/scooter tires to be used; except that the tires used MUST be
D.O.T. approved for use on public highways. No other distinction is made. But one should
check the laws where their bike is licensed to be sure of requirements/limitations, etc.
because in some places like England (possibly the whole of Great Britain) the practice of
using a car tire on a bike is banned/prohibited.

I sent inquiries to several insurance companies and got mixed results in their responses.
From all the responses I did get, AAA of Michigan was the only insurance company to state
outright that they would not honor a claim if the bike had a car tire on it at the time of
an incident/accident. Others have had different answers from companies that they had asked
about using a car tire on their bike. Many of the responses cited it would depend on
circumstances of individual cases and claims. (rather non-committal in my view)
Here is a link to post on BurgmanUSA site regarding insurance and the use of a car tire on a

Trailer tires should never be used on the driven wheel on the rear of a MC/scooter. (nor the
front) Trailer tires are free wheeling and generally are not built to handle acceleration
and braking forces incurred by a MC/scooter.

In the days of the past, car tires had been used on the front of some motorcycles, possibly
because that was all that was available. Nowadays, motorcycles have been known to use a car
tire on front, but only in special circumstances. Such as one might find on a motorcycle
with a side car or a non-leaning trike. Most (but not all) side car rigs have the bike
upright all the time with no leaning and sometimes use a car tire though there have been
recommendations against doing that too.

Car tires have been used on motorcycle trikes on the front, but most frequently are mounted
on just the rear. Trikes in general do not lean. Reverse trikes (2 wheels in front + 1 rear
wheel) have been known to use car tires all around and remarkably, there is at least one
instance of an individual using car tires successfully all around on his Piaggio MP3 400, a
reverse trike that can lean in turns.(though he admits to steering feeling heavier and
generally would not recommend it to others.)

Often change only comes slowly and with some struggle. It might be wishful thinking, but the
idea of getting bike rims that will properly accept car tires or very car like tires that
will fit properly onto bike rims would be a pleasing prospect. Some day maybe, but it seems
today is not that day. There are a couple examples of custom fabricated/modified wheels that
use car rims mated to the bike's driven hub.

Forum postings and Other Technical & safety items regarding use of car tires on bikes.

(these, with some editing/revising from Yahoo groups hondareflexowners that deal with the
Honda Reflex scooter where a car tire being used is about 1 inch taller overall than the OEM
scooter tire)

> It WILL affect the handling of the scooter.
True, but so will adding accessories like top boxes or panniers, taking on a passenger and/or
gear different than stock windscreens, and changing from old to new tires. Even changing
brands of tires can affect the handling, and not always in a positive way. Several posts in
various forums speak of displeasure with the handling and wear of some new tires of some

A tire as it gradually wears, gradually changes how it handles. Seldom does one toss their
new tires just because they feel squirrely at first nor do they change tires at the first
sign of handling change due to wear. Most riders adjust and compensate and continue to ride
safely all the while anyway until they need to change tires due to wear or unforseen damage
like a screw or nail puncture. I have adjusted to how the car tire feels and handles and I'm
confident and accepting of it's handling and performance. It's not hard to do at all. People
adjust, compensate and accept change in things all the time.

> If it is larger in diameter it will raise the rear end and subsequently reduce the caster
> of the steering (and the tendency to go straight), reducing stability especially at high
> speeds.
You do realize that an adjustment to the shocks will make a difference to the angle the bike
takes when loaded? And that the weight of the rider can change the angle of caster in a more
significant way? That wheel end of the swing-arm can jump up and down more than .5 inch just
during normal riding down your average street? (There is 4.7 inches of travel to the rear
shocks of the Reflex BTW) A lift of .5 inch is negligible, especially since it is 60.8" away
from the point where the front wheel contacts the ground. The car tire I have on one of my
scooters is a total of 1.062" inches taller overall than a standard scooter tire. + 0.531"
taller radius = 0.531" rise. With a wheelbase of 60.8 inches, 1° needs 1.061 of rise. But it
is only 0.531" of rise. That 0.531" rise equates to an angle change of only 0.5°, just one
half of one degree! A more intuitive way to think about it would be; While using a standard
scooter tire, back the bike up onto something that is 0.5" thick to simulate the raising of
the swing-arm caused by the car tire... Now tell me, how much do you think that really
affected the fork angle up front? ... Not much I dare say!!

> If car tires were good for motorcycles and scooters everyone would be doing it, and
> scooter tires would be made more like car tires.
Not necessarily everyone. This is still a relatively new concept for scooters and a lot of
people still don't even know about it yet. Even if everyone did know, there would still be
many that wouldn't do it. There are a few that have a car tire on their scooter now. As time
goes on and more people learn about it, there will be more that will put on a car tire.
Anyway, it is good for me. It could be that more scooter tires will eventually have some
similarities to car tires. Pirelli now has a Radial tire for scooters in a size that can fit
on the Reflex.

(An edited message of mine from
Quote from: (user name hidden)
> These are my thoughts and hearing them from an engineer just makes me feel a little more
> that way. On the other hand it could be that the design engineers never thought about car
> tires. It would be interesting to see if a tire company that makes the appropriate size
> car tire would have one of their engineers work up whether they think that their tire is
> safe on a motorcycle.
end quote

My response (edited):
The idea of testing car tires on motorcycles has been presented to engineers before but was
declined due to liability issues. That was their claim, and understandably so for these days
in such a litigious society that we have. But, surely testing could be handled as it is done
in aviation. They use willing and able test pilots paid to do the job of testing and already
have the liability issues worked out. The tire industry insurance/liability argument against
testing is weak IMO....

It is not likely any time soon that bike engineers will come up with a design for a bike
tire that has the attributes of car tires that the Dark Siders enjoy. Likewise it is just as
unlikely that car tire manufacturers would develop a car tire that would perform the way
that most bike tire users would like. That's the way it is now... they make tires for cars
after all.

Probably the most influential design aspect that divides the 2 types of tires is the
planform; The bike tires are made with a more rigid sidewall to help support to the arced
tread face giving them a more rounded profile. That makes for a smoother transition from
upright to lean and having a contact patch of relative consistent shape for more consistent
handling and feel throughout riding angles. This is not how it happens with the full width
flat plane of a car tire tread. But the sidewall compresses along with the tread face that
partially flexes to keep tread on the pavement even when leaned. Granted, it is not as
graceful or consistent like the rounded profile of a bike tire provides, but certainly has
not been proven to be dangerous... even anecdotally. In use it works well enough. It is
predictable and consistent in its own right though the feel, handling and control is
different than with a bike tire with its rounded profile. That is one thing the naysayers
have a problem with. Because it is different. It looks different and handles different. But
different does not automatically mean dangerous. A new tire is different than a well worn
tire that a rider has safely ridden with. And most certainly has adjusted his riding to
accommodate that worn tire.

It is this rounded planform that makes bike tires tend toward wearing faster than car tires.
They could use much harder rubber for longevity, but in doing so would be lacking in safe
grip. They could go with a wider section with flat tread, but would have the same handling
aspects that might be considered less than desirable by some riders like car tires exhibit
on bikes. It's a trade off with not a whole lot of room to trade. It is this physical aspect
that even with current technology and materials, even the brightest engineers would have
trouble engineering a way around to get a bike tire to last near as long as a car tire yet
maintain the desirable attributes of rounded profile bike tire handling.

I am pretty sure it has crossed the mind of engineers and they have noticed that car tires
last longer. I'm sure they try to make tires that have better longevity. Economics dictate
that. Make a tire better than the competition and you'll sell more of your tires. But I also
think they know it is in large part due to the physical differences in car tire design;
design differences that do not lend well to bike tire handling that they see their bike tire
buyers wanting. So while they don't really see (yet) or have great demand for such a tire,
there is little impetus to try to develop one either. A viable market for that just does not
exist in enough numbers (yet) to make it worthwhile for them. The goal for designers is
guided by the need for smooth and consistent handling at any speed; a car like tire would
perform outside of that because of handling aspects brought on by the wide flat tread area.
Other exotic or innovative designs would need to be brought forth and developed to bring
bike tire longevity up to par with car tires.  

I think they could make a tire much like a car tire with an appropriately fitting tire bead
and sell to the big cruiser bike crowd so that they would buy their tires instead of using
car tires. If there is any real market for a tire like that it would be the big cruiser
bikes. Darksiding is already getting to be a popular aftermarket option/modification by
owners for those kinds of bikes. I'd really enjoy seeing something like that happen. First,
it would be seen as a boon for the big bike riders to finally have a bike tire that has good
longevity while still providing acceptable handling, performance and good grip. (Secondly,
my views would be vindicated.)

Bike tire manufacturers have been nudged in this direction as evidenced by the relatively
new radial tires for bikes. And innovative use of varying rubber compound hardness across the
tread; hard along the centerline for longevity and softer compound toward the edges for grip
in turns. See!, they seem to have noticed car tires after all. And they might even be able
to develop a tire that does fit on a bike rim as it would on a car and would last nearly as
long. But it would probably look like a lot like a car tire with wider tread that would
spread the load and wear across a wider section. However, it would still probably exhibit
the same less than desirable (to most riders maybe) handling characteristics of a car tire.

From a message on the site
> > > > > > > > > > > > > > > > > > > > > > > > > > >
> Quote:
> Originally Posted by (name hidden)
> I'll tell you what really concerns me about this whole scene, and it's not really the
> riding of Dark Side bikes; it's the lack of comprehension of real risk. "….explains that
> motorcycle tires and corresponding motorcycle rims are designed with a bead seat diameter
> and flange contour that are different than passenger tires/rims and that ANY ATTEMPT TO
> MOUNT a passenger tire on a motorcycle rim may cause inflation pressure loss or the beads
> to break WITH EXPLOSIVE FORCE and the result could be SERIOUS INJURY OR DEATH."

And it keeps getting explained that Dark Siders do understand there is risk in riding and
that there are design differences. Then there are those that don't understand that Dark
Siders are willing to take that risk partly because there is not enough evidence of terrible
things that might happen actually ever happening; mostly they don't happen. And if they did
It would be reasonable to expect that we would hear of such things happening. But we don't
hear it because it doesn't happen with enough frequency to be any more of concern than what
might happen while mounting car tires to car rims or bike tires to bike rims. If there is,
then show us.

> Quote:
> Originally Posted by (name hidden)
> This should be pretty clear. A blowout off a rim, which is possible when a tire does not
> fit a rim is potentially pretty serious business. Combine that with the high pressures
> people are using to force the beads to seat on an incompatible rim, and it should be a
> This is a serious risk of blowout people are running with likely fatal consequences. Do
> Dark Siders truly understand the risk that they are running?
> This is not about whether the tires will stay on the rims once mounted; but the danger of
> forcing them onto the rims in the first place.
> (name hidden) showed in his response that he doesn't even comprehend the nature of the
> problem.." whatever your paranoia about car tire not conforming to the shape of motorcycle
> rim/ wheel is a non-issue."
> > > > > > > > > > > > > > > > > > > > > > > > > > >

As above: We understand there is risk. But if these terrible things are happening in a more
than proportional way than bike tire to bike rims or car tire to car rims, then show us.

> > > > > > > > > > > > > > > > > > > > > > > > > > >
> Quote:
> Originally Posted by (name hidden) View Post
> Tire changing is not something that fools should be messing with it's serious business.
> People can get hurt. I'm done here.
> > > > > > > > > > > > > > > > > > > > > > > > > > >

I don't mount the car tires onto the rear rims of my bikes. I don't have the tools or the
know how for that. I leave it to the tire changing professionals who are well versed in the
risks of mounting ANY tire and know what they are doing. And so guess what? If there ever
was a place that was risk averse to liabilities like that, you wouldn't think a major
metropolitan motorcycle power sports dealership would even consider touching a car tire to a
bike rim. Or other tire shops for that matter. Yet that is what happens with regularity at
more than just one or two places all across the country. Lots of them will do it without

There was only one customizing shop that was a bit squeamish about doing it for me once, but
they did it anyway. And never was it ever mentioned at any of the dealerships or tire shops
that they thought it was a bad idea or that I needed to sign a release of liability or any
other kind of waivers.

Got a beef about car tires being mounted on bike rims? You might want to consider taking
your concerns to them and call them fools; if you think that will help with the idea that it
is wrong and without merit. I think you and some others were already done with this a while

And here, a partial message from a member on site:

"Something else to remember is weight. A fully dressed out HD bagger weighs about the same
as a Smart Car! A scoot may simply not weigh enough to allow a hard car tire to get a proper
grip even when it's dry."

My edited response, in part to that:
"He also mentioned vehicle weight, but his assumptions are incomplete regarding coefficient
of friction and weight. After all, a tire will have virtually the same amount of weight that
will be pressing onto the contact patch whether it is a bike tire or car tire on that bike.

To make a point, a softer rubber is going to have a higher coefficient of friction than a
harder rubber on samples of equal size (*see note below) on equal surface textures and
temperatures and bearing equal weight. Car tires use a softer tire compound; so if softer
rubber = higher coefficient of friction and that = more grip then it's easy to conclude that
a car tire would have better grip than a bike tire.

And car tires have a softer rubber compound in part because of more silicates in the rubber
compound mix to help with better grip in wet and cold conditions. And those are conditions
where bikes are at a higher risk of traction loss. (well yes, and cars too... but the point
was made here for bikes)

(*note) For the bike, the "equal size" will be true if both the car tire and the bike tire
used on the rear of that bike happen to have same size contact patches. Most times, but not
always, a wider tire carrying the same amount of weight at an equal air pressure will have a
slightly larger contact patch. And tires of identical width but are differently constructed,
have different aspect ratios or are of different diameter may possibly have contact patches
that would be of different sizes. (and possibly differently shaped as well)

An Information Service Bulletin from the Rubber Manufacturers association

I have NEVER seen nor heard about any of those things in that warning ever happening. That's
not to say that it doesn't ever happen, but it has not been reported enough times to make it
much more of a concern than tire puncture and loss of pressure.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Here is a rather comprehensive post from someone from a Goldwing forum.

This more than covers a lot of the things presented here in this "THE DARK SIDE" (according
to bandito2), though it is more oriented to the big bikes. The guy did a tremendous job of
gathering information. I would say even if you read no further in my presentation here, by
all means, do read the posting on the Goldwing forum by this person. Admittedly, much of it
is not flattering to the idea of DarkSiding. But it is an honest attempt at not being
completely biased on the matter. One should know as much as they can about some things. If
one is thinking about putting a car tire on their bike, then this is information they
should know... even if they don't completely agree with the degree of importance some of
those things hold. Better to be informed than not, even if that information does not always
support ones position.

Often the Dark Side debate revolves around traction, contact patch and tire compound
hardness and grip. That can be found toward the end of the first part of that comprehensive
post. Another point that is brought up is the bead/seat differences between bike tires and
car tires. Information on this is closer to the beginning of that message.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Here's a response to that post written by someone else that I paraphrase; a lot of which I
agree with, but moderated some of the points to better reflect my view. (CT= car tire & MT=
motorcycle tire)

"There is a load of good, technical DESIGN information in those articles on the differences
between car and bike tires, but is lacking in DYNAMIC APPLICATION information. (in other
words; actual testing) I do not deny the different design aspects. Each tire and rim was
designed with a purpose in mind. However, the historical application data (reports by people
that use a car tire on their bikes) suggests these differences fall short in relevancy. The
question I have is this: If MTs are the wise and proper solution for the motorcycle, why do
MTs continue to catastrophically fail with regularity, putting the rider at risk? There is
absolutely NOTHING in the presented information to investigate the causes of these failures.
Until the MT manufacturers construct a tire that can be reliably safe, comparable to a CT, I
won't consider putting one back on my bike. I will live with the "theoretical" risk of the
CT on a MT rim, rather than the higher "demonstrated" risk of the MT".

And more interesting info on tire wear:
A debate on tire wear and turn dynamics is discussed here at this link. Darksiding manages to
get mentioned.

Some technical info on motorcycle tire dynamics... A Lot of formulae here so it may or may
not be helpful with the Dark Side debate one way or another. But it certainly is interesting
how testing was done.

General tyre properties v cornering.

Tyre pressure effect on stability

Article about motorcycle tire wear.
From that site:

Articles from Rider Magazine:

Letters to the Editor in response to that article (several are scathing some praise the
article) Most responses seem to object to the author's bias against using a car tire on a

Here are links to some threads on the site:
They are quite long, but you'll see a lot of the arguments from both sides over various
points of the Dark Side debate. It's a lot to wade through and some of the messages are
tedious, ridiculous and a waste of time and space. But there are some interesting nuggets
throughout. Admittedly, some of the information seen there is not completely correct and may
require sorting/filtering.

Calling all dark siders

Car tire on my Burgman 650

car tire size for Vstrom ??? (Pros and cons of car tire on a bike)

Dark Side Video Cam

DANGER, DANGER!!! (and other random musings)
I'm not crazy, stupid nor too cheap to buy "real" motorbike tires for my ride, I just choose
not to. And if one does not do things within the scope of influence, advice, knowledge
or even without the approval of designers and engineers do things necessarily become
automatically dangerous. Knee jerk reactions are seldom correct. (and there do seem to be
some jerks when this subject comes up to this day still.) Engineers and the rest of the so
called educated don't know everything. And theories not backed by actual physical testing do
seem to take on an air of dogmatic rhetoric by paper tigers. Besides, this world is full of
educated idiots. Experience and first hand knowledge are a better and truer gauge because
they demonstrate the truth in an absolute and undeniably solid way. And the preponderance of
evidence thus far (and there is plenty of it) has shown that using a car tire has not been
proven to be unsafe. (IMO....jeez, but it's torture being PC these days)

From > Riding > The perfect line and other riding myths > Stupid questions
people ask you when stopped.
The banter I sometimes get from gas station gawkers goes something like this:
=] Gawker: Hey it looks like you got a flat tire there man.
=] Me: No it isn't flat, it only looks that way because it's a car tire.
=] Gawker: Wow! really? (steps back and eyes my bike with a dubious look)
=] Me: Yes really. Works as well if not better than a scooter tire.
=] Gawker: Isn't that dangerous?
=] Me: Well no, I don't think it is. But if it is dangerous then your car there is 4 times
=] as dangerous since it has 4 car tires on it. (me grinning, but knowing just how true that
=] statement is.)
From a message of mine from (edited)
So we Dark Siders just use car tires on the rear. And for those who dare, MC/scooter rear
tires up front.

Tire aesthetics (how it looks) is not the only reason Dark Siders use a car tire.
(subjective, but it is a partial consideration for some)

Tire performance on rough pavement/gravel/dirt roads in general is not the only reason Dark
Siders use a car tire. (May depend on actual type of riding done, rider skill and conditions
while in use. Admittedly subjective as it is with aesthetics. But they are used mostly for
paved public roads and gravel/dirt roads may generally not be a point of consideration for
some users.)

Tire tread longevity is not the only reason Dark Siders use a car tire.

Tire strength/durability is not the only reason Dark Siders use a car tire. (strength in
reserve because it is loaded lighter than it is with a car)

Tire cost is not the only reason Dark Siders use a car tire.

Tire change frequency is not the only reason Dark Siders use a car tire.

Tire performance in braking is not the only reason Dark Siders use a car tire. (based on
claims by nearly all users and considering higher coefficient of friction of softer car tire
rubber compound... Testing would need to be done to confirm better braking.)

Tire performance on wet roads is not the only reason Dark Siders use a car tire.

Tire speed rating and load capability is not the only reason Dark Siders use a car tire.

Improvement of speedometer accuracy is not the only reason Dark Siders use a car tire.
(Depends on whether speed is derived from the rear wheel and if car tire diameter is larger
than the standard bike tire.) Typically bike speedometers display an optimistic reading of
speed. A bike using a taller tire will gain some correction on the speed displayed. The
caveat with a using a taller than a standard bike tire is that it may show less than actual
miles traveled on the odometer.

Improved fuel economy (if car tire is taller than standard bike tire) Lower engine rpm's for
given speeds when compared to a standard stock tire plus benefit of lower rolling resistance
is not the only reason Dark Siders use a car tire.

Most of these combined, if not all and more are reasons why Dark Siders use a car tire on
the rear of their bikes.

End of the road (for now)

In the end, Dark Siding is a practice that some swear by while those that oppose the Dark
Side practice will just swear at it. The controversy and debate will likely continue until
comprehensive, unbiased, methodical, scientific physical testing is done to determine
comparative values of suitability & safety between car tires and bike tires in various modes
of use and conditions. Not only to determine if car tire use on a bike is safe
(or dangerous), but the level of safety and usability in comparison to bike tires.

But even then, I think people are going to do what they want to anyway... That is the way it
is now. People have put car tires on bikes in spite of all the opposition to it. The only
way it might be stopped would be through rigorous enforcement of any legislation that may be
imposed regarding car tire use. That would not go down without a fight. Government intrusion
into the every day minutiae of the citizenry is bad enough as it is already here in the USA.
No need for micro management in attempts to impose the misguided notion that we need to be
saved from ourselves.

So that's pretty much my version of the Dark Side story as I see it. And I do reserve the
right to change my mind about things, so I won't be setting this in stone... Even I have
changed my mind about some things along the way to this point. So I am open to clarification
of items and correction of errors to help make it more complete and accurate.

Number of posts : 43
Location : Rochester Hills, Michigan
Registration date : 2008-07-11

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