Wheel Colliders & Jumping.

So I'm back, with a new question.

Somehow the following script doesn't seem to work with Wheel Colliders:

if (Physics.Raycast(transform.position, -transform.up, 2)) { grounded = true; } else { horMovement = airModifier; forwardMovement = airModifier; grounded = false; }

    //jump if the user pressing the space key AND our character is grounded
     if (Input.GetKeyUp(KeyCode.Space) && grounded)
         rigidbody.AddRelativeForce(transform.up * jumpForce, ForceMode.Impulse);

I first thoug it could be my gameobject but I checked several times for this. Somehow the Wheel Colliders is interfering with my raycast script. Any ideas? Do I have to rewrite the whole thing, to match the Colliders or is there a simple, faster way to do so? :)

Thanks for taking the time to read this! :)