What keeps the wheels from going through the ground in the car tutorial?

Hello,

This may be a silly question and I'm probably just missing something but...

In the Unity Car Tutorial what keeps the wheels from going through the ground?

I've been playing with this for hours and I still car figure out what keeps them from sinking through the floor while the car is driving, because colliders just stop the car from being able to drive.

Thanks.

the unity car tutorial (as the most of the driving game around, included the hardcore simulations) uses raycast to check if the wheel is "touching" the ground. if this is the case, the compression of the suspension is calculated and the wheel model position is changed accordingly with the raycast hit distance. Its not a good solution to use colliders for this cause most physic engine suffer of numerical errors with fast rotating objects