Use this Hop-Up Option set to allow superior acceleration on low-grip surfaces and improved stability under braking. The use of a front direct coupler (A.K.A spool) replaces the oil-filled gear differential, found in the XV-02 base kit. By eliminating the differential action, at the front of the car, the car will have more stable braking power and increased forward drive because the wheels have no differential action that result in different rates of wheel rotation. The side effect with using a front direct coupler is less car rotation through corners. Use this option part depending on your running conditions and Rally track layout.