[ODE] Car simulation wheel problem

[Erin Catto]

Here's my experience trying to use rigid body wheels:

Well, I tried creating rigid bodies for wheels. They have nice traction and
braking behavior but I ran into other problems. At high speeds (~60mph) the
wheels would lose alignment. Perhaps this could be mitigated by using more
iterations and/or smaller time steps. Another effect I didn't anticipate is
wheel tunneling. Now that can be reduced by ray casting, but this means the
wheel won't keep up with the chassis. I guess I could put in special logic
to slow down the entire vehicle, but I didn't try that.

I went back to my ray casting model and tuned it a bit more. I found a trick
that really improves handling. Basically, I just offset all traction,
braking, and friction forces up from the ground. The helps to diminish roll
and pitch. This can't easily achieved with rigid body wheels.