the physics of tire traction.....read if buying tires!

[Dominic]

lol good one bob [img]smile.gif[/img]

[Drone51]

bob knows all!!!!!

[KBeezy]

V6Bob, I agree, but I never said anything about brand and tire type NOT making a difference. My whole point was two identicle tires, one narrow and one wide, will provide for different results in traction [img]smile.gif[/img] Tread pattern as well as tire pressure, tire temp, tread life, road conditions... All of those factor in with traction of the tire [img]smile.gif[/img]

[HAZ-Matt]

Does anyone kow the "real" friction equation? All of the ones that appear in the introductory level textbooks were empirically derived. From snooping around the internet, I only found vague references to the fact that friction was poorly understood even now... so is there even an "advanced" equation?

[AZ3.8Camaro]

It's hard to explain, but on a physics 101 level, the simplest way I can put it is sure, the width does not effect the normal force, but it does change the overall coefficient of friction.

Think of it on an atomic level, atoms are essentially pushing by one another, they bump, it causes friction. A wider tire will have more rubber molecules bumping more "street" molecules.
Whats going to bump harder, 245 guys or 275 guys?

[AlienInv8r]

There isn't going to be one definitive "advanced" friction equation. Your road surface varies so much with every inch you move; look at asphalt and how many thousand different contact areas your tire makes while just sitting still. When engineers develop tires they have to spend a ton of time measuring frictional coefficients and various stresses from numerous angles to develop tread patterns and rubber compounds. Then you have to factor in all the cost vs performance variables and things. Most advanced and real-world physics, statics, dynamics type problems take a lot more than just one simple calculation. That's why they invest so much money into research and devolopment because it's pretty intensive and time-consuming.

[arthansen]

Acording to my Engineering "Statics" book:

"The magniude of the limiting static friction force Fs is independent of the area of contact provided the normal pressure is not great enough to severly deform or crush the contacting surface of the bodies".

This means that if the tires did not deform (made of steel) then the area of contact would not matter. However, tires do deform and thus the area does matter.

Oh, the real friction equation has so many variables it is useless, that is why you never see it. Real world test data is the only viable way to comare tires.

But here it is:

F=uN1 + uN2 + uN3 + uN4 + uN5 + ....

Where Nn is the normal force at each point of contact between the tire and the road (I am talking molecular level contact). There would be billions of these contact points on a normal tire.

If you took two of the same brand and model of tire, with the same air pressure, one 255 mm wide and one 245 mm wide, the 255 mm tire would grip better. Width matters. Not as much as the type of tire but all else being equal, width is what counts.

[ December 09, 2004, 12:40 AM: Message edited by: arthansen ]

[HAZ-Matt]

Originally posted by arthansen:
Acording to my Engineering "Statics" book:

thankyou

[Ike]

Originally posted by ellik:
.....and with winter coming on us (at least those of us that drive our RWD's in the snow) the rules change yet again. the wide tires that we enjoy during the summer distribute the weight of the car over a larger area and apply less force to the slick ground, giving less traction than narrower rugged designed snow tires.

This isn't right. What happens with snow is that your tires will "plow" it into a bump in front of them. This acts as an impedence to their motion and causes them to have to work harder to move forward--and in doing so, will lose their grip. (and some hand-waving to simplify the problem)

This is why a good winter tire is skinny: It doesn't cause the plowing problem.

[arthansen]

Snow?????

[Joe Racer]

College physics can only do so much. numbers on paper do not always translate into real world performance. to set the record straight, what works for cornering will be different from what works in a straight line.

In typical straight line performance whether it is braking or acceleration, you want the largest footprint from front to rear. To obtain this, you want as tall of a tire and as narrow of a tire as possible to acheive the desired performance. This footprint will be larger from front to back than in width. This is the opposite of what you want in a cornering situation. In this set of variables, you want a contact patch as large as possible in width, and a tire height that is shorter than in a straight line. This footprint will be wider than it is long (from front to back) and favors side load resistance. Most of us will have to compromise as we aren't all strictly drag race or strictly autocross. You can apply as much 'friction' math as you wish, but if you don't size your wheel and tire combo within these guidelines, you will not get the desired results. Size does matter! ;)

[FuryCharger]

u guys are looking way to deep into this haha. All i wanted to do was to provide incite into tire traction. And for the record yes i would take a 225 tire over a 315 tire anyday if it had a greater traction rating. When taking into account real life scenarios then yes expanding the tires width will increase the opportunity for parallel forces to act on the tire but those forces are to little to be accounted for. The equation is not accurate in all real life cases but it is true in a general sense. You cant argue with an equation. And to hear people say that the more tire area u have is more contact area pisses me off cause its far from accurate. you could have a tire that is a mile long but if it is covered in grease it wont do anything. DONT FOCUS ON WIDTH BUT TRACTION RATING!

[arthansen]

Focus on BOTH.

[Joe Racer]

Originally posted by FuryCharger:
u guys are looking way to deep into this haha. All i wanted to do was to provide incite into tire traction. And for the record yes i would take a 225 tire over a 315 tire anyday if it had a greater traction rating. When taking into account real life scenarios then yes expanding the tires width will increase the opportunity for parallel forces to act on the tire but those forces are to little to be accounted for. The equation is not accurate in all real life cases but it is true in a general sense. You cant argue with an equation. And to hear people say that the more tire area u have is more contact area pisses me off cause its far from accurate. you could have a tire that is a mile long but if it is covered in grease it wont do anything. DONT FOCUS ON WIDTH BUT TRACTION RATING!

I gotta say that part of what you say makes sense, other parts are off in left field. I'll say it again..... you must take into account the intended useage before you can even remotely try to pick a wheel and tire combo. This has been going on for since the dawn of automotive performance. What works for cornering doesn't necessarily work for drag racing. To even suggest a mile long tire soaked in grease is a ludicrous analogy that shouldn't have even been mentioned. I'm not trying to start any flame way, I've been racing since the 70s and probably have more seat time than anyone on here. The shape of the contact patch is critical. If you put a sticky tire with the wrong shaped contact patch there will be virtually no benefit. I will guarantee that the same make and model tire will require a different size depending on whether it is a dragstrip use or a road course use. If people don't choose to believe it, their loss. They will get eated alive in a race by more savvy folks that do understand it. The biggest problem with equations are that there are too many variables with intended useage. Confine the useage to one specific control and the equations will have more bearing. I do agree a sticky tire is better than greasy one, but other than that.... well, it's already been covered. [img]graemlins/popcorn.gif[/img] It's not really all that complicated. That's why a formula one car doesn't use a 33 inch tall tire, and a top fueler doesn't use a 26 inch tall tire. That is taking things to a little more extreme, but it should give you something to think about.

[arthansen]

I Agree, focus on all three, height, width, and traction rating. Look at these in refrence to what you want to use them for and how long you want them to last (the last one is a big one).