This is a direct mount Rear Dura-Ace R9100 brake caliper for under bottom bracket position mounting on only direct mount compatible frames. The Dura-Ace R9100 Brakes are Dual-Pivot design Brake Calipers with the best balance between rigidity, weight, and stopping power. More predictable, clear contact feeling also creates a more linear braking curve for modulation and control previously unavailable on rim brakes.. The new sleek design has less gap between each arm and allows for tire clearance up to 28mm for super comfortable riding on rougher roads The entire DURA-ACE R9100 groupset is the result of Shimano’s ongoing passion for technology. This is reflected in every single component in the groupset. All components are joined together to work as one, reinforcing each other for unparalleled performance. This is how DURA-ACE achieves ultimate supremacy.