Detecting collisions without rigidbody

I have a car with the following aspect:

As you can see, colliders are locally static, because they are separated from the original rigidbody component.

Well, as you can suppose, I have a problem, because MonoBehaviours with an OnTrigger(...) or an OnCollision(...) method won't work. (It needs an rigidbody and a collider on the same object)