The Shimano RD-6870-GS is the medium cage rear derailleur for the 6870 series.
It supports a max front difference of 16T, a low sprocket minimum of 28T and a low sprocket maximum of 32T. The top sprocket maximum is 12T and the minimum is 11T. It has a total capacity of 37T and weighs only 11g more than the short cage derailleur - 268g.
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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 the BT-DN110 battery, synchronized shift is enabled for this derailleur. Read more on synchronized shift in the complete guide to synchro shifting.
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.
