4 ms·

That equation works for friction between idealized solids. Tires are not even close to an idealized solid, they deform as more weight is added to them, so the c

by lpapez 3y ago

That equation works for friction between idealized solids. Tires are not even close to an idealized solid, they deform as more weight is added to them, so the contact surface area increases as more pressure is added. That is why you see racing cars with big fat tires, because it's more grip and the relationship is not linear.

ars 3y ago
The equation still holds. As the tire deforms to have more area the pressure on any particular part of the tire is lower. The total friction is unchanged. > That is why you see racing cars with big fat tires If you mean drag racers those tires are glued to the ground, and do not work off of friction. Other than that, what race cars have big fat tires? Tires are usually sized so that the ground pressure of the tire is in the 40 to 100 psi range (which is also the tire inflation pressure). That's simply to keep the ground from deforming and the tire from popping. It does not affect friction. This is also why off-road tires have lower pressure - the sand and mud they work on is not strong enough for a higher pressure. It is NOT for increased friction, it's because the surface they drive on can't handle it, so you spread out the weight, and reduce the pressure.
coryrc 3y ago
They have the fat tires because they're purposefully melting tire rubber into the pavement for a bit more traction. Rubber tires have maximum grip at 7% slip; just about the only material where sliding friction is greater than static friction. Road-going tires won't get hot enough unless you're skidding far below 7% slip.
caf 3y ago
That friction equation comes originally from empirical experiments, not from idealised models. The explanation in fact relies on deformable surfaces. If you imagine keeping the normal force constant and reducing the apparent contact area, the pressure on the surfaces will be increased which will cause the surfaces to deform more, resulting in more microscopic points of adhesion.
- caf 3y ago
  (If you find this surprising and want to read a little more, try this: https://www.stevemunden.com/friction.html https://www.stevemunden.com/friction.html)

by lpapez 3y ago

ars 3y ago

The equation still holds. As the tire deforms to have more area the pressure on any particular part of the tire is lower. The total friction is unchanged. > That is why you see racing cars with big fat tires If you mean drag racers those tires are glued to the ground, and do not work off of friction. Other than that, what race cars have big fat tires? Tires are usually sized so that the ground pressure of the tire is in the 40 to 100 psi range (which is also the tire inflation pressure). That's simply to keep the ground from deforming and the tire from popping. It does not affect friction. This is also why off-road tires have lower pressure - the sand and mud they work on is not strong enough for a higher pressure. It is NOT for increased friction, it's because the surface they drive on can't handle it, so you spread out the weight, and reduce the pressure.

coryrc 3y ago

They have the fat tires because they're purposefully melting tire rubber into the pavement for a bit more traction. Rubber tires have maximum grip at 7% slip; just about the only material where sliding friction is greater than static friction. Road-going tires won't get hot enough unless you're skidding far below 7% slip.

caf 3y ago

That friction equation comes originally from empirical experiments, not from idealised models. The explanation in fact relies on deformable surfaces. If you imagine keeping the normal force constant and reducing the apparent contact area, the pressure on the surfaces will be increased which will cause the surfaces to deform more, resulting in more microscopic points of adhesion.

caf 3y ago
(If you find this surprising and want to read a little more, try this: https://www.stevemunden.com/friction.html https://www.stevemunden.com/friction.html)