The steering rollradius is the distance between center of the wheel road-contact area up to the piercing point of the extended steering axis of rotation by the roadway, it facilitates the steering control of the vehicle.
The steering rollradius results from cooperating camber, spreading and insertion depth of the wheel; three possibilities result:
Steering rollradius positively, zero or negatively.
The term " negative steering rollradius " became by the introduction with Audi in connection with the diagonal brake system in particular admits, because a negative steering rollradius has a stabilizing effect on the travelling straight ahead with on one side pulling brakes or with asymmetrical roadway resistances.
Normally if a vehicle is inclined to pull toward the more strongly braked wheel then this reaction is transformed by a negative steering rollradius into the opposite. The braking force pivots the wheel to the not braked side, whereby lateral breaking out of the vehicle is avoided.
Settling shims between disk wheel and wheel hub or the use of rims with other insertion depth changes inevitably the steering rollradius determined during the vehicle development and concomitantly the handling of the car.