why do car rims stick to the tire instead of spinning?


Especially on high power cars this always confused me, I know quite a bit about cars but I never got this.

In: Engineering

Bacause the fit very tight on the wheel. For high power and off road applications they make beadlock wheels.

Friction, the same reason your tires stick to the ground until a certain amount of force is applied. The difference is that friction exists on all 360 degrees of the rim. Incidentally, they do sometimes slip in racing applications.

The fit or “bead” of the tire is extremely tight. So tight that it takes a pneumatic device to remove it most of the time. It is also glued on there in many applications,but the glue is more for sealing or making sure it doesn’t leak air than to hold it on.

There is *a lot* of force pushing the bead of the tire into the rim.

Lets say your tire overlaps with the rim by about 0.25″ around the edge and you’ve got 16″ rims, that gives you 12.4 in^2 of contact area on each side of the tire for 24.8 in^2 total. Well your tire is probably pressurized to somewhere around 30 psi and this pressure pushes in all directions, including forcing the rubber of the tire against the rim. With your 24.8 in^2 of contact area you get 744 pounds of force holding the grippy rubber against the rim of the wheel.

This is a lot of force and the friction between rubber and steel is decent so you’ll have a lot of friction there, hopefully more than the resistance the tire has to rolling on the ground otherwise the tire will spin on the rim.