Shimano XTR M9100 2-Piston Disc Brake Set. Model: XTR M9100(Left-Rear+Right-Front UK Version). Shimano XTR M9120 4-Piston Disc Brake Set. Model: XTR M9120(Left-Rear+Right-Front UK Version). With a repositioned clamp band and lever body, situated closer to the centre to increase stability and improve comfort and braking power.