Cassettes-7 Speed. Cassettes-8 Speed. Cassettes-9 Speed. Cassettes-10 Speed. Cassettes-11 Speed. Cassettes-12 Speed. Model: RS31-6 speed RS31-7 speed. Number of gears: front 3 speeds + rear 6 speeds = 18 speeds Front 3 speeds + rear 7 speeds = 21 speeds.