Read This on Another Forum(Good Read)

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Read This on Another Forum(Good Read)

Post  rrounds on Tue Jun 26, 2012 11:35 am

...........WOW...another thread full of opinion, half truths, misdirection, and other stuff like that. Well-meaning comments that just are not the truth.

Welcome to Physics 101. Credentials: 25 years total in two university Physics Departments. Degrees in Physics and Mathematics from famous schools. Bla, Bla, Bla. Kind of an expert in basic motion dynamics. Taught a ridiculous number of classes on this, so here it is according to Galileo, Newton, Descartes, et al...

Disclaimer: This is serious stuff, and most smart folks have to work at it for a while before it sinks in. NOBODY gets this with a light skimming. I sure didn't! Oh, and it's TRUE. Physics has a 400 year history of testing and refining and testing some more. It's OK with me if you want to believe something else, but you are NOT smarter than Galileo and Newton. You have NOT spent years and years running experiments, trying to figure out what it all meant. They did. I did.

Contact patch area is simply not important to the friction between tire and road (or you may call it traction if you like).

1. How much force is on the tire matters. We have the weight of the MC pushing down on the road (W). The force that the road exerts on the MC upward is called the Normal Force. (N) In our simple example, they are equal so long as the road is flat. W = N.

2. How well the rubber sticks to the road matters. We call this the Coefficient of Friction. (u)

CRUISER, you seem to mostly have the right idea mixed in with some misdirection...BUT how hard you can corner is a different question than whether contact patch area matters. I will address both.

Friction Force available = (Coefficient of Friction)*(Normal Force)

FF = u N = u W


Some excellent info in other posts above about why dragsters use wide tires...as well as some misdirection. Wide tires are a more stable platform, can continue to grip even when there is sand or dirt or oil or an uneven surface. Wide tires allow for rubber to be shed under hard use without heating the tire as much, and the same amount of rubber loss is less thickness lost with a wide tire. A lower pressure can be used for a given load, increasing comfort. A wider tire tracks straight more easily. Lots of good reasons, none of which have anything to do with traction.


On to cornering. There are several ways to approach this, but here is what I do:
Friction available is some fixed quantity. The friction a rolling tire has with the road is STATIC friction. This sounds wrong at first, but the tire is not slipping against the road surface, which is what matters. Think about just that tiny contact patch. Is the tire making firm contact with the road, or is it sliding? Firm contact, even though the contact can be very brief. STATIC.

If the tire was slipping and sliding, that would be dynamic (or kinetic) friction. Static friction is ALWAYS greater than dynamic friction, so when the tire starts slipping even just a little, friction is reduced, and you start to slide even more. NOT GOOD, and down you go if you cannot stop the tire from sliding.

Draw a circle. This is the path you are taking, and the MC follows the circle. Which direction are the forces on the MC? Gravity (weight of the MC) is DOWN. Normal Force (pavement holding the MC up) is UP. Notice that these directions are independent of the motion of the MC! The same whether the MC is stopped, going straight at constant speed, acceleration, turning, stopping, whatever. Weight = Normal Force, assuming the road is flat. Let's keep assuming that, since it makes the problem simpler.

Hey, almost time for some maths!!

Look at the circle, and imagine the MC going around. Imagine the same kind of motion, except with a marble on a string. What makes the marble change direction? The tension in the string. What makes the MC change direction? Friction between the tires and the road. If you try the marble spinning with a thread, you can spin the marble faster and faster, but at some maximum speed, the thread breaks.

Similarly, you can go around a corner on the MC faster and faster, and at some maximum speed, the tires slide out and you fall. What IS that maximum speed?

1. Maximum speed depends on the radius of the turn. The larger the radius, the greater the maximum speed. This is pretty intuitive.

2. Maximum speed depends on the coefficient of friction. Stickier tires, and rougher surfaces, are better for high speed cornering. Also pretty intuitive.

3. Most folks expect the weight of the MC to matter. Stay tuned...

Friction Force (FF) is the thing that makes the MC turn. Simplest case is flat road, constant speed, constant radius turn. You already know that FF = u W.

In circular motion, the force that is turning the object is W V V / g R.
Here, W = weight, V = velocity (twice), g = acceleration of gravity (9.8 m/s/s or 32 ft/s/s for Americans), and R = radius of the circle. All this is still true if the road is not flat, or the radius is not constant, or speed is not constant. You just have to add some calculus to our little algebraic expression. Not today.

Most of the time, there is more friction that you need. The critical point occurs where your need for turning force exceeds the available friction force. Just like the marble and the string. This occurs when the two forces are EQUAL.

u W = W V V / g R

Solve the equation for the velocity and a couple of interesting things happen.

V V = u g R

V = [u g R] to the one-half power, or the square root of [u g R]

Maximum velocity depends on gravity (essentially constant), the radius of the turn, and how sticky the tires are. NOT the weight of the MC at all.


Hey, I love this stuff...but...is anybody still reading? Thanks if you are. Flame on if you like. But a lot of smart folks spent a lot of time on this problem, and this is the TRUTH......


Did you get that ? I got some of it and then he lost me(been 37 years since college) and I have forgotten way to much. Crying or Very sad

ROD

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read this on another forum good read

Post  Larry Simpson on Tue Jun 26, 2012 11:57 am

I also have been out of college far too many years but did comprehend and agree with some of what was said but reconize some of it to be what works out on paper and theory not to be true when actually applied in the real world. thumbup thumbup
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Re: Read This on Another Forum(Good Read)

Post  GEARHEADFLA on Wed Jun 27, 2012 2:43 pm

HUUMMMM Some people have WAY to much time on their hands, let me see if I can explain my thoughts on this, I put the tire on and it worked, End of report. ROFL
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Re: Read This on Another Forum(Good Read)

Post  twin1300 on Wed Jun 27, 2012 3:58 pm

I just use the Darkside factor to figure this.


Every 40 miles or so, I have to stop and get off the bike and let my ass laugh the ride is so smooth!!!! Ppwwwwwahahahahahaha



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Re: Read This on Another Forum(Good Read)

Post  CaribCruiser on Wed Jun 27, 2012 9:28 pm

You've studied too much Bobby ! Laughing

twin1300 wrote:I just use the Darkside factor to figure this.


Every 40 miles or so, I have to stop and get off the bike and let my ass laugh the ride is so smooth!!!! Ppwwwwwahahahahahaha



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Re: Read This on Another Forum(Good Read)

Post  smokey2255 on Thu Jun 28, 2012 3:23 am

plus1
CaribCruiser wrote:You've studied too much Bobby ! Laughing


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Re: Read This on Another Forum(Good Read)

Post  quadancer on Thu Jun 28, 2012 9:55 pm

Static friction is ALWAYS greater than dynamic friction, so when the tire starts slipping even just a little, friction is reduced, and you start to slide even more

Uh, Yeahhhh...except he forgot to figure in HEAT factors of the slipping rubber, in where it INCREASES dynamic traction - the reason the racecars zigzag before a takeoff, heating up their tires for traction.
It goes on, but there IS some truth to the SMALLER contact patch having MORE traction given the same weight load. Yep, there it is fellas, "blaaasphemy" in the high degree. You don't see super swampers on those cowboy pickups who deliver hay to the cows in winter, no, they use a skinny MUD tire that will dig down to hard surface where the traction is. The cows depend on it.
In similar situations, a leaning bike, loading its edge treads is on a slightly thinner patch than when straight up. But what happens there? Force spread over area, still a constant, is multiplied. So, we are left with the ONE other factor that makes any difference: the static friction, which is determined by the rubber of the tire.
So, can this hack tell me that the harder bike tires are going to grip better, inch for inch, than the softer CT? And can he tell me (or show me pretty numbers) that prove that the BT's have more contact than the CT's in a sweeper?
Funny that all I've ever seen is just the opposite.
Yeah, I'm a Darksider. I defend our right to run them and our belief by experience with them. I defend their toughness, longevity, and performance, INCLUDING in the parking lot cones, where I teach the RLAP style of riding. I take on any comers running MT's to ride North Georgia, although I got a bit tired of waiting for them to catch up at times.
Why someone will take a cruiser to a challenge riding with MT's against a CT under a stone crazy old man what ain't afraid to die is beyond me. BUT, I look forward to the next one!
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Re: Read This on Another Forum(Good Read)

Post  Doc on Fri Jun 29, 2012 11:59 am

All I ask is that the one's saying it can't be done,

get out of the way of the one's doing it... lafer

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Re: Read This on Another Forum(Good Read)

Post  jedishon on Fri Jun 29, 2012 2:00 pm

My math tells me: Put me on my ride (C) in America (A) on any road (R) at any time (T) and it will be an interesting (i) ride (r) everytime (e) or CAR Tire.

Jerry
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Re: Read This on Another Forum(Good Read)

Post  twin1300 on Fri Jun 29, 2012 2:11 pm

00 Doc wrote:All I ask is that the one's saying it can't be done,

get out of the way of the one's doing it... lafer


lafer lafer lafer lafer lafer lafer Now that's funny!!!!



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Re: Read This on Another Forum(Good Read)

Post  speedsville on Fri Jun 29, 2012 2:58 pm

I raced Formula Vee's for 30 years.
With our 5.5 inch tires, we could corner just as fast as a Formula Ford with an 8+ inch tire.
I proclaimed for years that friction was independent of area.

I believe that to be true even of a rolling tire but there are some other factors there that make some difference, I can't
get hold of what or how.,,

To the OP it would be best to include a legend of what each symbol in your formulas means.
Otherwise is looks like you are just spreading the manure.


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Re: Read This on Another Forum(Good Read)

Post  Otis56 on Fri Jun 29, 2012 4:20 pm

So what was he really trying say, sounds like round 2 from rider magazine lafer
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Re: Read This on Another Forum(Good Read)

Post  speedsville on Fri Jun 29, 2012 5:08 pm

It is pretty obvious a cut and paste.
I've thought a lot about the friction/traction/tractive effort situation and really can't prove it one way or another.

I've done the lab tests which show friction independent of area (static) but adding latteral forces on a rolling tire seem to add
something else.
Yet as I wrote, my 5.5 in tire would corner as well as the 8+ inch tire.
Weights of the cars is about the same and no downforce.

But some designers who are smarter than me on this tell me there is a difference. Shrug
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Re: Read This on Another Forum(Good Read)

Post  rrounds on Mon Jul 02, 2012 2:26 pm

speedsville wrote:.....It is pretty obvious a cut and paste....
Hell yes I cut that out of another site.
When I was in collage I had to use a slide rule(because that's all there was) Laughing I think I still know how to use it to(if I could find it). thumbup
I like my 175/75-16 tire that I run on the back of my VT1100-T, get about 3 times the mileage out of it and it rides so smooth.

ROD

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Re: Read This on Another Forum(Good Read)

Post  quadancer on Mon Jul 02, 2012 7:46 pm

...and grips so gggooooooooood! Yeh, mine forgot to look at those equations too.
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Deliberately obfuscating

Post  Sillyshishi on Thu Aug 30, 2012 11:13 am

I think this guy is deliberately trying to make his thing more confusing in an to confuse people and convince them that he is smarter than they.

Here is what he said, how he should have said it:

"I've got a ton of degrees, but this little gem comes from basic high school level physics. Contact patch (textbook) has no true effect on friction. You see, the weight of the motorcycle is the same no matter what your contact patch size is. The larger contact patch, therefore, causes this weight to spread out more and therefore reduces the PRESSURE (expressed in pounds per square inch) exerted. The narrower the tire, the harder it "pushes" against a road. The harder something pushes, the more friction it generates. Friction is a coefficient of pressure and surface area of contact. assuming force (weight) stays the same, as your surface area (contact patch) increases, your pressure decreases. This means that all other things staying the same, traction will not change for wider or narrower tires."

Basically, this argument really only reduces the nay-sayer argument that car tires can't grip as much in corners because they ride up on the edges. The more a car tire "rides up on its edge" (which we all know isn't really what happens if the rider has set the pressure properly) the harder it pushes against the ground as it distributes the same weight over a smaller area.

This, however is not QUITE true in the real world. The wider your contact patch, the more irregularities in the road that the rubber is working its soft little self into as you go along your merry little way. This increases traction a little, even though they aren't being pushed into quite as hard. A wider tire also loses a smaller percentage of its traction with running over something on the road, such as gravel. Therefore, this man's argument really only serves to weaken the naysayer stance and strengthen ours.

Long story short? Regardless of contact patch size, traction is [about] the same in perfect conditions. The true traction modifier is the hardness of the compound making relations with the road. In imperfect conditions (what I like to refer to as "real life") things will be in the road to impede grip (gravel, sand, debris) and the wider tire has a greater capacity for maintaining its traction in these situations.

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Re: Read This on Another Forum(Good Read)

Post  quadancer on Thu Aug 30, 2012 1:10 pm

From a discussion in the motocampers forum on tire pressures (originally for trailers, but denigrated or upgraded
to DS) a truthful article that demonstrates in LAYMAN'S TERMS, friction coefficients. My only problem with the whole
article was their comparison of MT's to CT's inasmuch as they just used one of each.
http://www.stevemunden.com/frictiontopics.html
You guys are gonna love this one. -g
edit: let's keep in mind that wider may handle finding grip in adverse conditions, but it has a tradeoff in handling to
some degree (more crossover effect), and more tendency to track offcamber surfaces. This is why I prefer narrow,
which in a CT, is still pretty ding-danged wide on a bike.
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Re: Read This on Another Forum(Good Read)

Post  locopony on Fri Aug 31, 2012 8:09 am

I did a lab test when I did construction. I was an Iron worker. You can not slide a 20 foot long 6x6x3/8 angle iron across roof truss beams on one of the 6inch flat sides but you can if you roll it over so that it is sliding on the two 3/8inch edges. In fact you then can quite easily. Same weight, same roughness, different contact area, extremely different results. Contact area matters.

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Re: Read This on Another Forum(Good Read)

Post  quadancer on Fri Aug 31, 2012 8:23 am

That is because you are comparing a flexible medium to a solid. The solid (steel) would have more drag by area
as one might expect with tires, only the flexibility of the rubber evidently allows for more grip over a lesser area
I would suppose due to it's ability to indent over irregularities.
I would wonder what the friction coefficient would be of rubber on steel though. What is there to grab?
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Re: Read This on Another Forum(Good Read)

Post  locopony on Fri Aug 31, 2012 12:17 pm

I know I was over simplifying, but only trying to make an easy point of contact surface area matters. Its not the only factor but a biggy. Granted if you were to place that same steel on rubber you could nog slide it at all. Structural steel is actually quite rough and the rubber would grip that in a tremendous way. Especially with 3 or 400 pounds of steel pressing down on it.
When I lived in the north the lakes and ponds would freeze over so to have fun we would ride bicycles on that ice. That was a case of shear contact not helping much. You need very sharp points to digg into that stuff inorder to have any traction. The more sharp points the better.

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