The Shimano Ultegra RD-6870-SS is a short cage rear derailleur for Shimano’s Ultegra 6870 11-speed electronic group. It is designed for road cyclists who want fast, exact shifting and compatibility with compact or standard road gearing. The derailleur mounts to a standard hanger and is constructed from aluminum for durability and low weight.

This model suits riders who prefer cassettes with a maximum rear cog of 28T, typical for road racing and fast group rides. The short cage design keeps weight down and provides crisp shifting, especially with smaller rear sprockets. The RD-6870-SS is compatible with Shimano 11-speed road cassettes (Shimano or SRAM) and requires a Shimano Di2 electronic shifting system for operation, including compatible shifters and battery.

Key features include Crash Protection Mode, which prevents further shifting after a crash until the derailleur is checked—reducing the risk of additional damage. When paired with the BT-DN110 battery and newer Di2 components, it supports synchronized shifting, allowing for automatic front and rear shifts under certain setups. With a low installed weight (about 257g), this derailleur is a solid choice for riders looking to maintain a traditional road gearing setup and want the reliability of electronic shifting without the bulk of a medium or long cage.