HPI Fiber Brake Disk for the Nitro RS4 Racer Series. Replaces worn Fiber Brake Disk. Made from pressed composite fiber material. This product includes one fiber brake disk. ). Part for Nitro RS4 and Nitro RS4 Mini kits delivers increased stopping power and less brake fade during long races. The new Fiber Brake Disk is perfect for nitro racers that have upgraded the speed of their cars with out 2 speed transmission or tuned pipe. The heavy duty fiber disk can easily handle the extra load, and it's thicker than stock for extended life. This part is a direct replacement for all HPI Nitro kits and is a stock part replacement for Nitro RS4 Racer kits. Fits Nitro RS4, Nitro RS4 2, Nitro RS4 RTR, Nitro RS4 Racer, Nitro RS4 Racer 2, Super Nitro RS4, Nitro RS4 Mini, Nitro RS4MT, Nitro RS4MT RTR, Nitro RSMT Racer, Nitro Rush, Super Nitro Rally.