How to reduce torque of wheelCollider when a collision takes place ?

I've done the following: ![alt text][1] [1]: /storage/temp/206612-code.png RoueArrièreDroite, RoueArrièreGauche, RoueAvantDroite and RoueAvantGauche are all wheel colliders. This code uses the gas input of my Logitech pedals to add torque to the wheels, allowing my car prefab to move forward. The problem is that when my car collides with another gameObject, the torque on the wheelColliders stays the same, making my car move at the same speed. Is there a way for my car's speed to decrease when it collides with another object?