Tamiya Hop-Up Options 22047 XV-02/TT-02 Front Direct Coupling Set (39T)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