Double Darkside Warning (Motor scooter specific)

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Double Darkside Warning (Motor scooter specific)

Post  bandito_two on Sun Jul 11, 2010 9:52 pm

I posted the following on a few scooter groups I frequent. It is mostly aimed at scooter users, but very well may be useful info for
motorcycle riders who are already using, or considering the use of a rear bike tire up on the front. I know motorcycle dynamics may be a
bit different from scooters, but I'm just sayin.

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As some of you know, I have been riding with a Pirelli 150/70-13
scooter rear tire on the front of my Reflex in place of the standard
110/90-13. It was an extension of the practice of also having a car
tire on the rear. I will not advocate for the practice of using a
scooter rear tire on the front and infact STRONGLY advise against it.
However, I am still OK with the use of a car tire on the rear.

Of the 1090 miles using the rear tire up front, the last 400 miles
or so were nearly all expressway speed miles. The previous 690 miles
were at 65 MPH or less. (mostly 55 MPH and less) The last 100 miles
riding near 70 MPH and above (expressway speeds) were the most
telling AND alarming and are the reason for this warning and advice
against using a larger, wider tire up front.

The problem is high speed instability with DANGEROUS steering
oscillation occuring as the severe symptom especially when initiated
by the tire going over a substantial surface irregularity. (a bigger
than usual bump or hole in the road) It is exacerbated and more
pronounced while in a sweeping high speed turn.

Maybe some of you have experienced this in a high speed curve after
hitting a bump and the front end starts to wobble left and right a
bit while the front tire "hunts" for its latitude track line on the
tire. To understand what I mean by latitude track line, visualize a
globe on its side with the equator line vertical and as the contact
track line of the tire when the bike is straight up. Imagine it then
in a turn where the tire touches the road and now the tire rotates on
a latitude line north or south of the equator depending on which way
the turn is. Disturb this by going over a bump or hole in the road
and what happens is the steering will be caused to diverge from where
it was miliseconds previously, and moreso if the bump or hole is not
a straight-on edge but has a left or right angle to it. It is subtle
in its movement, but profound in its effect. The tire may actually
have left the surface of the road. And in a turn, if the tire leaves
the surface, it is no longer following the arc of the turn, but
rather continues in the line of momentum. When it lands, the tire
grabs and tries to move everything in the new direction. An extreme
example of this would be a bike doing a wheelie but before the front
wheel comes back down, the steering gets turned. You can pretty much
imagine what happens then when it touches down!!!

The tires, shocks, steering components, frame and the weight that is
carried on a bike are NOT as rigid and immoveable as one might think.
There is room for movement and shifting of weight and force (and it
does) of varying intensity occuring concurrently all throughout the
matrix of man (or woman) and machine and road while riding along.
Problems show up when there is not enough dampening between these
forces which allows oscillations to begin and intensify if not
controlled. Having the wider tire on front makes it easier for
oscillations to occur and intensify especially at higher speeds.

So what happened was, on the way back home to Michigan from the AMA
Vintage Motorcycle Days event down in Ohio I was hitting the
regularly spaced expansion joints in the road that were swollen from
the day's heat and got this just as regular thump, thump, wobble,
wobble, wobble as the front and rear tire each went over those bumps
in rapid succession. It was, to say the least, disconcerting and
downright frightening especially when I hit a deeper pothole on a
straight section of the highway. WHAM, wobble, wobBLE, WOBBLE,
WOBBLE, weave, weAVE, WEAVE, WEAVE, WEAVE, WEave weave, WOBble
wobble, wobble. When going over the expansion joints, I noticed that
it worked better to tuck my eblows in, tighten my abs and hold the
hanlebars in a slight pushing way rather than try to hold back on the
bars in a slight pull in an attempt to dampen the steering
oscillations. In hindsight it seemed then that to pull or hold back
on the bars merely allowed my arms to be flexing springs whereas
using my arms as limiting pushrods, it kept the handle bars from
diverging too far, thus limiting the depth of the oscillations. It
happened so rapidly that I was one or two more weaves from TOTAL LOSS
of control and would have been pitched to the pavement if I wasn't on
top of it right away slowing down and attempting to limit the
weaving. And as this was happening, the bike was gradually drifting
to the left coming perilously close to the rumble strip on the left
edge of the pavement. I was thinking "If I hit that, I'm hamburger."
I was also aware that if I did go down, I wouldn't get run over
because other vehicles were far enough away, but close enough that
they saw my high speed wobble/weave happen. In fact, the car behind
me did a quick light flash. Kind of like a "slow down buddy, I just
saw what you did" At least that's how I thought of it. So it was no
more than 65 MPH the rest of the way home and no more wobbles at all.

You would think I'd chuck this tire and be done with it. I know full
well the consequences of an incident at highway speeds, but also know
so far that it only occurs at highway speeds. I'm going to keep this
tire on in spite of that knowledge, but will adhere to a strictly
self imposed speed limit and use the Silverwing scoot for slab
slinging.(after I get it fixed) NO MORE expressway riding with the
Reflex... PERIOD. Even if It gets a standard tire on front. IMO now,
the Reflex, while able to get out onto the expressway, doesn't mean
it should. The incident shook me up that bad. Another person might
have peed their pants, but Hey, I'm not just another person.

So for the purposes of this warning, I will declare the 'scooter rear
tire on the front' experiment a failure. Don't do it. Seriously. Take
it from somebody who survived and averted a seriously close call and
knows better.

Mike B.

(Rochester Hills Michigan Double Dark Side Rider)*

(2007 Honda NSS250S Reflex Sport "Scarlet")
(2006 Honda FSC600A Silverwing "Jester")

* Double Dark Side not recommended...
... Just regular Dark Side maybe =8-)

==== While knowledge has power, It is what you do with what you
know that is important.
It gives the knowledge validity and demonstrates its worth.
Use it wisely. ==== (I wish I knew more)

Number of posts : 44
Location : Rochester Hills, Michigan
Registration date : 2008-07-11

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Re: Double Darkside Warning (Motor scooter specific)

Post  motorcyclereb on Mon Jul 12, 2010 5:56 am

I have ridden with a rear tire on the front for over ten years. The only time I ever expierenced anything like what he talks about is when my tire was low on air pressure or out of ballance. Not saying it wont happen just that I have never experienced it.
Uber User
Uber User

Number of posts : 146
Age : 63
Location : Ocean Isle Beach, North Carolina
Registration date : 2007-12-15

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Re: Double Darkside Warning (Motor scooter specific)

Post  quadancer on Mon Jul 12, 2010 8:18 am

Sounded pretty weird to me, but I wouldn't run one in front as a rule anyway = the MT's get good mileage up there and have a different job than the backs. There's a lot of difference between leading and trailing. I'd also wonder about braking on the front in a curve if you had to: wouldn't the edge of the tire tend to pull the bars over more? Of course, that would make you straighten up and give you more brake, but what if you didn't WANT to straighten up?

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Re: Double Darkside Warning (Motor scooter specific)

Post  bandito_two on Fri Nov 15, 2013 9:37 pm

Well, after about 3 1/2 years and coming across several posts on various forums that reminded me, I'm back to update on doing the double darkside on my scooter(s)

It was a balance issue and once it was resolved, there were no more headshake/control problems. In fact it gave my scooter even more stability while pulling my single
wheel trailer. Still, I would say one should proceed with caution and be aware that doing the double darkside is even more different than doing just a car tire on the rear.
The handling is even more different and may make some uncomfortable with the different feel. But one can adjust. I did and decided that I like it for what I use it for.

Anyway, it seems as time moves along, ever more people are going darkside on the big scooters; Suzuki Burgman and Honda Silverwing FSC600 scooters especially.
I have even seen where some trikers are putting car tires all the way around on both types of trikes; conventional (2R, 1F) and reverse (2F, 1R) Alas, there are still
many out there without a clue and will never try the darkside. Just as well I suppose. ("These are not the tires you are looking for"......"Move along citizen") Suspect 

Not quite the crusader I once was, but I am still a champion and defend the darkside and point out the error of many of the naysayers assumptions and disinformation.Vader

Number of posts : 44
Location : Rochester Hills, Michigan
Registration date : 2008-07-11

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Re: Double Darkside Warning (Motor scooter specific)

Post  rrounds on Fri Nov 15, 2013 10:42 pm

rexkaru who rides a MP3 400 darksided his scoot with all car tires. He has over 10k miles on them now and has no complaints in those miles.
Look about half way down all the way to the bottom of this page



Number of posts : 256
Age : 62
Location : Sacramento, CA
Registration date : 2008-06-06

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Re: Double Darkside Warning (Motor scooter specific)

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