I loved working on this car rig. And I love the result I have achieved so far. I rigged the car using bones, IK, standard Max controllers and scripted controllers. My primary aim while developing this rig was surface detection, so that the car could travel on any uneven surface. The end user doesnot have to worry about spinning the wheels, or steering the front wheels and more importantly, wheels touching the rugged terrain. The scripted rig takes care of all that.

Script WIP :

In the process of developing a scripted tool to rig up any 4 wheel vehicle.
Sample Car Rig :

The vehicle model is downloaded from 3dcafe.com