Scrub radius positive: produces stable straight-running stability but requires counter-steering by the driver in case of uneven braking effect
Scrub radius negative: in case of uneven braking effect, provides automatic counter-steering so that the driver only needs to hold onto the steering
Scrub radius zero: prevents the transfer of faulty forces to the steering in case of one-sided pulling of the brakes and in case of tyre defect, high steering forces at a standstill.