RENTHAL Staal zelfreinigend voortandwiel 496U 520 Amount of teeth:13 teeth APT is a proprietary compound APT is a proprietary compound that emulates the feel and touch of aluminum levers PROX bearing + crankshaft key sets allow you to overhaul the crankshaft with the same reliability as the original and therefore maximum power transmission to the rear wheel Excellent compromise between efficiency and sustainability