The Shimano RD-6870-SS is their short cage rear derailleur for the 6870 series.
It supports a max front difference of 16T, a low sprocket minimum of 23T, and a **low sprocket maximum **of 28T. The top sprocket maximum is 14T and the minimum is 11T. It has a total capacity of 33T.
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It also features Shimano's Crash Protection Mode - this prevents shifting after a crash to make sure the rear derailleur is damaged any further. To restore shifting functionality have a look at the FAQ: I had a small crash and my rear derailleur stopped working.
When paired with 6870 or newer components and the BT-DN110 battery, this derailleur supports synchronized shift.
Indexing, trimming, or fine-tuning Di2 rear derailleurs is done through micro-adjustment. Read how to set up your Di2 rear derailleur perfectly and ride without those grinding noises.
Bought a new Di2 rear derailleur and need some help installing it? Read how to install the RD-R8050 / RD-R9150 / RD-6870 / RD-9070 Di2 rear derailleurs.
Synchronized Shifting - what is it exactly? What does it do and how can you set it up? This page will guide you through the process of setting up synchro shift.
Shimano front derailleur and rear derailleur specifications... what do they mean, really? This page explains all of them, and why they matter.
