Originally Posted by thedoc
I wish my teachers had gotten their information right, In HS physics the teacher was talking about the co-efficient of friction and made the statement that surface area was not a factor and that people who put wider tires on their cars for more traction were not gaining anything. At that point I knew he was wrong about that and was more skeptical about the other 'facts' he was teaching.
According to this MIT lecture
, your teacher was correct. Though the professor acknowledges that it is counterintuitive, surface area does not affect the coefficient of friction. The coefficient of friction between a surface and object is found by taking the tangent of the angle where the surface needs to be tilted to in order for the object to slip. This is determined experimentally, and experimentally, objects of the same material will slip at the same angle even if they differ in surface area.
If you listen to the lecture, he actually assigns a homework problem in which the students must explain why racecars have wider tires even though it doesn't give better traction. I wouldn't have been able to guess the answer, but I checked the solution, which attributes the following explanation to The Flying Circus of Physics
by Jearl Walker (I don't know if it's supposed to be a direct quote or if he just got the idea there):
The frictional force on the tire does not depend on the surface area in contact with the pavement. Thus a wide slick is as effective as a narrow one. If the tires are spun over the surface as is often done in drag racing, then the wide [tires] have an advantage in that it has a larger surface area to heat and is less likely to melt. Melting greatly reduces the coefficient of friction.
You can find the solution set here
, that particular one is 3.10.