jschindler

In the three years since I've posted this it has become very obvious what the real answer is. Look at the tire choices Chevy makes on the new Camaro's, such as the ZL1 and Z28. They are putting various width tires - especially on the front, in order to adjust the handling balance. With zero physics discussion, I think it's pretty obvious that the bigger the tire the bigger the contact patch. I won't even be looking at this thread again because I believe the physics make sense for a static ball. But a tire is not static when rolling, accelerating, braking or turning.

tristenturner

you are right about the widths affecting handling but you are wrong about the contact patch size. the area only changes when the mass is changed. the width affects the shape (dimensions) of the contact patch. a thin tire has better straight line traction but loses out in turns. a fat tire is the opposite, not good linear but when turning it has improved grip.

you seem concerned about the mass shifting around during operation of the car, but what you are forgetting is when one tire has more weight, another tire has just as much less.

a thin tire also has the disadvantage of not being able to disperse heat well enough and will leave the rubber too hot or too cold to have proper grip.

the problems with dynamic tires do not become apparent until you are discussing scrub angles and sidewall height

so to recap, according to the physics of the world we live in, tire diameter and tire width have nothing to do with contact patch size, only the pressure inside the tire pushing out and the mass on the tire can change the contact patch.

that again is

psi x area = total weight on tire
OR
weight on tire/psi= area of contact patch

tire size can only affect the shape of the patch. 20 square inches can be a block 2x10 just as 20 square inches can be a block 4x5.

the shape affects handling of the car and the cooling aspects of the tires.

and again, the weight of the car when rolling, accelerating, or braking is not increased but shifted. so one tire will take the weight of the other. this has no effect on the average contact patch size of the tires, as 2 increase, the other 2 decrease.

i hope this clears everything up.

HOXXOH

Pretty cool when a new member with only 2 posts understands the concepts and writes a clear and concise statement.
Also pretty sad that some others can't grasp it, even after multiple explanations.
Maybe simple is better, so try this single sentence approach.
Irrespective of any other factors, traction is greatest in the direction of the length of the contact patch.

tristenturner

thanks, first i saw of this site was this thread. i happened to have spent the time to learn about some of the physics of traction and tires and was able to share some knowledge. kind of ironic that a google search on the effects the contact patch has on the auto-balance of a bicycle led me to this.