stop wheel colliders from sliding down hills

Hi!

Im making an arcade tank game, I tried using wheel colliders but I dont know how to use them properly, I added 8 of them to the tanks (to simulate tanks track) and added torque to all wheelcolliders but the tanks keep sliding down when going up hills, I know this is intentional behaviour of wheel colliders (they are simulating wheels after all!) but tanks dont behave that way, any idea how to prevent this?

Im using Unity 4.3 if that helps