With the previous 48 Pitch Pinion gears it was possible to change your gear ratio to match the course layout and get the best out of your car, but it was only available in 16T, 17T, 18T, 19T, 20T, and 21T gears. But now this new Option Part includes the 13T, 14T, and 15T gears. It is possible to use this item with TRF501X and DB-01 chassis. 　 Item Contents Pinion Gear (13T, 14T, 15T) x 1 3x3mm Grub screw x 3 1.5mm Hex wrench x 1 　 　 Possible Gear Ratios 　 501X DB-01 Pinion Gear Spur Gear 96T Spur Gear 91T 13T 16.62:1 14.39:1 14T 15.43:1 13.36:1 15T 14.40:1 12.47:1