defense style front unit, effective against aggressive rear units. Unit not only provides improved stability, but also extra speed. Simply clicks on to center unit replacing standard front unit. Front roller absorbs attacks while counter-attacking to knock your opponent off the track. Left and right side rollers help your racer smoothly navigate bends. A must have if your racer is fitted with a high powered motor. Numerous setting options with both 9mm and 11mm rollers included.