# Wider tires, Friction questions

by masscal
Tags: area, friction, independent, tiers, tire, tires, wider
 P: 28 So how do you edit the title of a thread...
 Engineering Sci Advisor HW Helper Thanks P: 7,119 Your textbook is not talking about real-world friction. It is talking about a simple mathematical model of friction, proposed by Coulomb about 250 years ago, which it is fairly accurate for hard materials (wood, metal, glass, etc) sliding at fairly slow speeds. That is the sort of friction experiment you would do in a ihigh school physics lab. The big advantage of Coulomb's "law" (or model) is that you can use it to learn how to solve mechanics problems, without needing a computer to crunch the numbers. There seems to be a lot of mis-information because some people have never learned anything except Coulomb's law, and think that is "everything" there is to know about friction. I'm not going to try to "explain" friction of car tires, but they certainly do NOT obey Coulomb's "law" of friction. The contact area of a tire does not depend on the size of the tire. It mainly depends on the air pressure. The total contact area of all the tires, times the air pressure, = the weight of the car. If you want to demonstrate that, just let some air out of one of your own car tires (but make sure you pump it up to the correct pressure again afterwards!!!)
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Wider tires, Friction questions

 Quote by masscal So how do you edit the title of a thread...
I took care of it for you.

BTW -- any time you want a thread or title edited, just click the Report button and ask the Mentors for help.
P: 28
 Quote by berkeman I took care of it for you. BTW -- any time you want a thread or title edited, just click the Report button and ask the Mentors for help.
thanks
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 Quote by AlephZero The contact area of a tire does not depend on the size of the tire. It mainly depends on the air pressure. The total contact area of all the tires, times the air pressure, = the weight of the car. If you want to demonstrate that, just let some air out of one of your own car tires (but make sure you pump it up to the correct pressure again afterwards!!!)
This is true, however the shape of the contact patch (which affects grip available) and the ability of the tire to withstand high heat loading (from high performance driving) are both affected by the size of the tire, which is part of the reason why wider tires tend to be preferred for high performance cars.