The Shimano Ultegra BR-RS811-R is a low-profile direct mount rim brake caliper built for the rear of aero road, time trial and triathlon framesets that locate the rear brake under the bottom bracket. Its SLR-EV dual-pivot design delivers a smooth, linear lever feel with strong, controlled stopping power.

• Direct mount rear caliper for under-bottom-bracket (chainstay) framesets
• SLR-EV dual-pivot mechanism for a light, linear action
• Aerodynamic low-profile body for clean integration with aero frames
• Clearance for tyres up to 28C
• Fitted with R55C4 cartridge-type brake pads
• Shares cable pull with Shimano 11-speed and 12-speed road levers

Built for aero framesets

Unlike a standard caliper, the BR-RS811-R bolts to two mounting points on the chainstays so it can sit tucked under the bottom bracket. This keeps the rear brake out of the airflow on framesets designed around a hidden rear brake, while still giving you a proper Shimano dual-pivot caliper.

Controlled, consistent braking

The SLR-EV mechanism and reshaped, stiffened arms give a progressive feel at the lever with consistent power under heavy braking. The angle- and pivot-adjustable pad holders run R55C4 cartridge pads, so pad swaps and toe-in adjustment are straightforward.

Compatibility & fit

Rear-specific caliper for under-bottom-bracket / chainstay direct mount framesets only; it will not fit a standard single-bolt caliper mount. Reach is 51mm and it suits external rim widths of 20.8-28mm with clearance for tyres up to 28C. The cable pull matches Shimano Dura-Ace, Ultegra and 105 road levers (R9100, R9000, R8000, R7000, 6800 and 5800 series, plus current 12-speed road levers). An inline cable adjuster such as Shimano SM-CB90 is required for cable adjustment and the quick-release function to work correctly. Confirm your frameset is designed for an under-BB direct mount rear caliper before fitting.