[masraum]

Your physics teacher was obviously no idiot or he wouldn't have been teaching physics, but it sounds like he was trying to apply simple theory and ideal behavior to the real world. In some ways that makes him an idiot. I had a physics teacher try to do the same with me in HS. He told me that all driveshafts were solid because it takes less energy to rotate a solid object than a hollow one. He was right about the last part, but the drive shaft in my '65 impala was most definitely hollow.

Part of the issue is that tire rubber can only withstand so much force before the rubber starts to shred and tear. By spreading the Frictional force over more rubber that reduces the force acting on each small area of rubber. Also heat is an issue and larger tires will not get as hot as smaller tires. Excess heat is bad for tire rubber.

Also, there's more to the friction that a tire makes than just the adhesion between the two materials. There's a great book on this of which the internet has a couple of really good excerpts. I'll find it and post.