The tutorials I've found show how to rig a wheel to roll automatically, in one direction (X or Y), in relation to the location of an empty or bone. I've managed to get the wheel rotation to work along both the X and Y-axis in a drivers-based rig, but the wheel rotation when steering on the Z-axis isn't always accurate.
A bones-based rig could possibly work if there's a way to set the axle or driver bone to local space, but I don't see a way to do this, and it might just result in the same issues as the drivers-based rig.
Your thoughts and suggestions would be appreciated.
The two rigs I've made are downloadable here, both controlled by the "ground" empty/bone.