^^ PytonPago, that is a genius idea. I would not have thought of doing that, but now I will be using it for sure! Just rotating chunks of a coil spring around center and moving them together should work well. Awesome!
... well, if you have some problems to see, how the spring is done, ive done a little research modelling and scripting ... just look at the stuf here :
forum.outerra.com/index.php?topic=3032.0Spring seems to work fine - its a little cheeky to make the spring itself, but i think it is worth the whyle at blender. Specially for some MonsterTruck action.