system
Given the following post, respond as if you're commenting on Reddit:
human
If the friction coefficient is independent of the surface area, why are tires on race cars so wide?

This question was posed at the end of one of the MIT physics lectures, but there wasn't any resolution.
gpt
Nice question, had me register to answer...

True, friction coefficient is not depending on the surface area, but in this case it is not the limiting factor. Just look at what happens when a tire *does* slip on the road: You see that it is not the friction between road and tire that is too low, but the "friction inside the tire", between rubber and rubber. You see that part of the tire still sticks to the road as a skid mark. It is the shear strength of the rubber that is not high enough, so a thin layer of it is sheared off and stays on the tarmac. Now, the shear stress *is* depending on the area.
Thus, a 20cm tire has the same friction on the road as a 40cm tire. But the 40cm tire has twice the surface area on the road, so they can spread a given shear force over twice the area, so their shear stress is half, so they fail (skid) later. Or, they can transmit twice the accelerating/deceleration/cornering forces.