"Inflation pressure does not affect grip": Autospeed article.

[dcb]

This is always worth bringing up, and a prime example of why "just test it" is usually the right answer (as well as being a reasonably documented test):

http://ecomodder.com/forum/showthrea...ures-2721.html

[winkosmosis]

Originally Posted by thatguitarguy

I can't tell if you are unable or unwilling to understand what I am saying, but it doesn't really matter because your return posts are confrontational and combative. You don't try to understand what is being said - you try to manipulate the words to suit your own purposes to give you something to argue against.

Race drivers don't want "WIDER TIRES", they want better traction. If they could get better traction with narrower tires, they would undoubtedly choose this option because the tires would be lighter and more aerodynamic.

Provide facts to support your argument, or just leave it alone.

You're the one who started with the confrontational crap, saying I need to take high school physics.

Why don't you just stick to arguing the topic at hand? Apparently you now agree with me about more traction with a bigger contact patch.

[Christ]

Civility is, apparently, lost on this thread.

[winkosmosis]

orange4boy, higher load increases the rubbers conformity to the bumps in the surface, but there is no rule that says the friction per unit area increases linearly with downforce. Halving your contact patch doesn't necessarily increase friction per square inch by 2x, so you can end up with less total traction.

If that weren't true race cars wouldn't run wide slicks to maximize surface area.

[Christ]

Originally Posted by winkosmosis

orange4boy, higher load increases the rubbers conformity to the bumps in the surface, but there is no rule that says the friction per unit area increases linearly with downforce. Halving your contact patch doesn't necessarily increase friction per square inch by 2x, so you can end up with less total traction.

If that weren't true race cars wouldn't run wide slicks to maximize surface area.

Do you have, or know, the math to determine friction coefficient? What variables would need to be covered?

I imagine that most of them would fall within a very tight range when only considering street tires that are normal use types.

[winkosmosis]

http://www.physlink.com/Education/AskExperts/ae200.cfm?CFID=23851351&CFTOKEN=3d5e2db7fc90c17f-AF97D314-15C5-EE01-B9F16054B94C5133

Question

As an engineer, I know that friction does not depend upon surface area. As a car nut, I know that wider tires have better traction. How do you explain this contradiction?

Asked by: Mark Secunda

Answer

This is a good question and one which is commonly asked by students when friction is discussed. It is true that wider tires commonly have better traction. The main reason why this is so does not relate to contact patch, however, but to composition. Soft compound tires are required to be wider in order for the side-wall to support the weight of the car. softer tires have a larger coefficient of friction, therefore better traction. A narrow, soft tire would not be strong enough, nor would it last very long. Wear in a tire is related to contact patch. Harder compound tires wear much longer, and can be narrower. They do, however have a lower coefficient of friction, therefore less traction. Among tires of the same type and composition, here is no appreciable difference in 'traction' with different widths. Wider tires, assuming all other factors are equal, commonly have stiffer side-walls and experience less roll. This gives better cornering performance.

Answered by: Daryl Garner, M.S., Physics teacher MacArthur High School, Lawton, OK


Friction is proportional to the normal force of the asphalt acting upon the car tires. This force is simply equal to the weight which is distributed to each tire when the car is on level ground. Force can be stated as Pressure X Area. For a wide tire, the area is large but the force per unit area is small and vice versa. The force of friction is therefore the same whether the tire is wide or not. However, asphalt is not a uniform surface. Even with steamrollers to flatten the asphalt, the surface is still somewhat irregular, especially over the with of a tire. Drag racers can therefore increase the probability or likelihood of making contact with the road by using a wider tire. In addition a secondary benefit is that the wider tire increased the support base and makes it hard to turn the car over in a turn or in a mishap.

Answered by: Stephen Scholla, B.A., Physics Teacher, Vienna, Virginia

[Christ]

That quote just told us all that wider tires do not create more traction, they only increase the likelyhood of maintaining contact with the road to use available tractive force.

There's a difference.

[winkosmosis]

Originally Posted by Christ

Do you have, or know, the math to determine friction coefficient? What variables would need to be covered?

I imagine that most of them would fall within a very tight range when only considering street tires that are normal use types.

I don't know what numbers are but I do remember hearing or reading somewhere that the coefficient of friction changes with downforce per unit area.

[winkosmosis]

Originally Posted by Christ

That quote just told us all that wider tires do not create more traction, they only increase the likelyhood of maintaining contact with the road to use available tractive force.

There's a difference.

I figured he was talking about a microscopic scale, as in better chance of bumps on the road biting into the rubber

[winkosmosis]

Here's confirmation of coefficient changing. Lower pressure --> higher coefficient of friction
*All Things Motorcycle* - Tire Traction. Is contact patch size important?

Foale, on page 2-27 of Motorcycle Handling and Chassis Design, says that "this coefficient [of friction] is not constant but usually decreases with vertical load. This effect varies between tyre types but the reduction is of the order of 10% for a doubling of load. A further complication is that this relationship is not linear. This has far-reaching implication and is one reason for the general increase in tyre section on racing and sports machines, because, for a given wheel load, the bigger the section the lower the contact-patch pressure and so the greater the coefficient of friction, hence grip on the road." (Emphasis mine again.)

Edit: He quoted the wrong page. It's 2-17