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Shimano Ultegra Di2 RD-6870 Rear Derailleur

Shimano Ultegra Di2 RD-6870 Rear Derailleur
Sale $151.63 - $169.45 $228.99 32% Off

Item # SHI0657

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  • Gray, Short Cage ($151.63)
  • Gray, Mid Cage ($169.45)
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Item # SHI0657


Light-years ahead.

Even though Shimano's Dura-Ace Di2 remains steadfastly at the top of the podium, Shimano's Ultegra Di2 6870 Rear Derailleur is sneaking in to steal the show. While many lower-tier brand name groupsets seem to muddy the waters of their higher-end counterparts, so to speak, we don't feel that's the case with the 6870 series. In fact, it features much of the same level of performance as the Dura-Ace group, without quite the sticker shock.

The rear derailleur received some exciting trickle-down love from Dura-Ace 9070, featuring a much slimmer profile than the previous Ultegra Di2 rear mech and also gaining the 11-speed shifting capability. The wiring has been cleaned up as well to ensure a very professional-looking kit, and the mid cage version can stretch to a 32t cog in the rear. The difference is mainly one of aesthetics and a few grams here and there. Where Dura-Ace Di2 uses custom servo motors, made exactly to Shimano's specs, its Ultegra Di2 derailleurs use off-the-shelf motors to drive the gear changes. The upsized internals determine the slightly larger overall package dimensions.

E-tube technology is what sends Shimano electronic shifting at such blazing speeds. The best features have resulted from advancements in the software, allowing you to customize shifting speed and even program how many gears the rear derailleur shifts through when holding the shift button down. The 6870 rear derailleur even has built in crash protection, forcing the rear mechanism to compact and tuck away in the event of an accident.

The 6870 Di2 rear derailleur offers shifting speed and quality that is on par with Dura-Ace 9070 Di2 — the best shifting performance that Shimano has offered to date. And with 11 speeds in the rear, the perfect gear is just a click away.

The Shimano Ultegra Di2 RD-6870 Rear Derailleur is available in both short and mid cage versions.

  • Slimmer profile
  • 11-speed shifting capability
  • Mid-cage accommodates a 32t cog in the rear
  • E-tube technology
  • Built-in crash protection

Tech Specs

Claimed Weight:
254 g
Recommended Use:
road cycling, cyclocross
Manufacturer Warranty:
3 years

Size Chart


Di2 Reference Guide


Note: This reference is meant to be used as a guide for creating a Shimano Di2 drivetrain package. For further assistance please feel free to give us a call.


Battery and Wires:

Our Shimano Di2 packages are built for three standard configurations based on battery location and wire routing. First, you'll need to determine if your frame uses an internal or external battery mount, and whether the routing is either internal or external. Below is a guide for which battery, charger, mount, and junction boxes are required for your configuration.

Battery and Wire Configurations
 BatteryBattery ChargerBattery MountJunction AJunction B

External Battery

w/ External Routing

SM-BTR1 SM-BCR1 SM-BMR2 SM-EW90 A/B 3/5 port SM-JC40

External Battery

w/ Internal Routing

SM-BTR1 SM-BCR1 SM-BMR2 SM-EW90 A/B 3/5 port SM-JC41

Internal Battery

w/ Internal Routing

SM-BTR2 SM-BCR2   SM-EW90 A/B 3/5 port SM-JC41

Battery Mounts:

The SM-BMR2 battery mount is available in three configurations -- Long External, Short External, and Long Internal. Both Long versions are to be mounted using the bottle cage mounts, while the Short version is designed for Di2-specific frames with either a chainstay or down tube mounting location.



There are two junctions needed for completing your Di2 build -- A and B.  Junction A, SM-EW90, is located at the handlebars and available in both three- and five-port options. The three-port option is intended for standard shifting with a left and right hand shifter. If you have the intention of using Shimano's satellite sprint shifters, or a combination of time trial shifters and shifter/brake levers, the five-port junction box will be the necessary selection.

Depending on your frame specification, Junction B (SM-JC40 or SM-JC41) is located either internally or externally at the bottom bracket area. Accordingly, SM-JC41 is designed for frames with internal wire routing, while SM-JC40 is intended for external wiring options.


E-Tube Wires:

For your convenience, we've created wire packages for your Di2 build kit in the sizes Small, Medium, and Large. Below, you'll find which wire lengths are included in each kit. Additionally, we've recommended a kit size based on your frame size.

 E-Tube Wire Length Chart
Down Tube Wire 700mm 750mm 950mm
Front Derailleur Wire 300mm 350mm 400mm
Rear Derailleur Wire 500mm 550mm 600mm
Battery Wire 300mm 350mm 400mm


 E-Tube Wire Frame Size Guide
Frame Size  47-52cm 53-56cm   57+cm

Please Note:

E-Tube Wire length suggestions are an approximation. 

Reviews & Community


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Bigger is Better

  • Familiarity: I've used it several times

Upgraded to the mid cage version to gain precious additional cog teeth. My previous version would only allow a 28t max rear cog while the mid version allow up to a 32t rear cog, which is more. And better if your bike likes to climb. Seamless installation, plug in, adjust limit screws and you are good to go. Shimano reliability is always appreciated.

Unanswered Question

Hey Guys,
I have a question pls. I smashed my RD Ultigra 6770 today. As you know this is 10 speed. I purchased the bike in first half 2014. So since I can no longer find 6770 can I use a 6780 for 10 speed. I don't need 11speed.

- Would I also need a firmware upgrade if I'm using it as 10 speed or not really?

- would I need to replace the cassette to 11 and also the chain? again I just want to use 10 speed.

Ultegra FTW!

  • Familiarity: I've put it through the wringer

I thought long and hard about a Di2 derailleur, Dura Ace or Ultegra. I'm VERY pleased with the Ultegra for a fraction of the price. Lets face it, it may be a few grams heavier but who cares!?!? This is bomber, it is up to the challenge of taking and beating and always delivering crisp, precise, and fast shifts.

Robot Bike

  • Familiarity: I've put it through the wringer

Whiiiiiiir Zip Beep Boop Beep

It occurred to me how crazy Di2 is, as I was running a firmware update on my bicycle. When Skynet takes over we Electronic Shifting cyclists are in trouble.

All Jokes aside though. 1600 miles on this drivetrain and not a single issue or adjustment needed. Every shift has been flawless, and barring any unforseen circumstances, like a crash or some good old fashioned garage or transportation mishap, I fully expect go 6000+ miles with no issues. The only drawback I can find, and this is totally a personal preference, but I sort of miss the mechanical drivetrain for no reason other than the simplicity of pushing a lever which pulls a cable which moves a derailleur. I would argue that the Di2 lacks tactile feedback when shifting, but that is just me nitpicking. I rode the battery until it completely died just to see what would happen. At about 1300 miles (this includes plenty of playing with the new group, shifting just to hear the sounds and show off the auto trim) The battery died on my 18 mile commute to work one morning, first the front derailleur refused to shift, after a few more shift button clicks it did shift down into the small ring, and I had about 30+ shifts of the rear derailleur before the system became unresponsive. So 1300 miles, I think it is safe to say a rider would need to be quite negligent to run out of power on accident.

Avg. ride time: 15h 35m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.


  • Familiarity: I've put it through the wringer

I've had the 6770 and now this 6870 and the work just like they should, quite, fast and precise. The 6870 is much smaller than the previous 10 speed 6770, the cable hides better too since the exit port come in the back between it and the seat tube. Don't spend extra for Dura-Ace, unless you get it at the same price, Ultegra is just like dura Dura-Ace, just a few grams heavier, diet for a week and your there.

Avg. ride time: 1h 46m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Durable & Precise

  • Familiarity: I've put it through the wringer

I've been extremely impressed with the performance of the Ultegra Di2 rear derailleur. I've logged considerable miles off road on my gravel bike, and while it's been banged around a bit, it hasn't missed a beat. It still delivers precise, quick shifts every time.

Durable & Precise

Reliability and value

  • Familiarity: I've put it through the wringer

This stuff works great and is super durable.


  • Familiarity: I've put it through the wringer

I purchased a bike with Ultegra Di2 about a year ago. It was my first foray into electronic shifting and it's just flat out reliable. The batteries last forever and you get quality dependable shifting. In the year that I've had it, I have had zero hickups.

I am currently running Ultegra 6770 Di2 10 speed drivetrain. Can I convert to the newer 11 speed by changing to a Ultegra 6870 rear and Front derailleur, cassette, and chain or will I need the new junction box too?

One bike mechanic told me that you need to replace the brake shifters as well because the 10-speed shifter only accommodates 10-speeds. Plus, there's the question of whether your old Di2 has an external battery that you'd like to replace and make it internal. In that instance you'd need wiring, the internal battery and a junction box too. One other potential issue is whether your rims can accommodate 11 speeds. I discovered that not all 10-speed rims can accommodate 11-speeds.

you can use your 6770 shifter, just need a firmware update and it's 11S ready, the rest you have to switch out even the junction box (referring to the Y type). you need the 6870 FD, RD, a 3 or 5 port junction box, new cassette and chains...I have the same setup...

Avg. ride time: 6m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

Solid, fast shifting

  • Familiarity: I've put it through the wringer

I've been riding this RD since last Oct. 2015 and it is awesome. Super quick, precise shifting RD that was very easy to install and set up.

Sticking with it!

  • Familiarity: I've put it through the wringer

Building a new bike is always exciting and it's always tempting to try new things. The drivetrain decision was particularly easy this time however, after my previous experience with Ultegra Di2. The light weight and sexy lines of the Dura Ace Di2 group are indeed tempting, but for the cost you can't go wrong with the Ultegra. I have had exactly :::zero::: issues with my previous group other than problems I have inflicted (read: derailleurs are not-crash-proof). This also makes the Ultegra a great option if you race, where close quarters and periodic pavement sampling are a fact of life.

Works great, easy to install

  • Familiarity: I've put it through the wringer

I bought this as part of an upgrade to 11-speed for my Trek Domane. Installing the derailleur was the easiest part of the installation. I got the medium cage because I wanted to use a 32-tooth cog on my cassette.

The derailleur was very easy to install. I don't have the special tool Shimano recommends for disconnecting and connecting the Di2 wire to the derailleur, but I did it easily with my fingers. I disconnected and unbolted the old derailleur and bolted on the new one. I connected the wire, and tested it - it worked immediately.

After putting on a new 11-speed chain, I ran through all the gears and it worked right away. Adjusting the Di2 is simple, first the limit screws and then the shifters. All 11 gears worked immediately, and the derailleur is fast and quiet. I've used it a lot on steep hills and on the flats, and it works like Di2 should - accurate, fast, and quiet.

Avg. ride time: 27m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

best der ever

  • Familiarity: I've put it through the wringer

I have no review that would actually convey my feelings for the DI2. I love this stuff, mechanical is dead, long live mechanical.

Flawless shifting, great value!

  • Familiarity: I've put it through the wringer

I have been riding a full Ultegra Di2 setup for more than a year and I am never going back to mechanical if I can help it! Why? Perfect shifts, front and rear, easy setup, expandability (currently using the

Flawless shifting, great value!

I am currently running Ultegra Di2 10 speed drivetrain. Can I convert to newer 11 speed by changing rear derailleur, cassette, and chain or will I also need to change shifters?

Best Answer


Ideally, you want the entire drivetrain to be Di2 but you can make do with rear derailleur, cassette, and chain. The front shifting won't be perfect, but it will work. Shifters, Wires, and battery don't need to be updated but you may need to plug them in for a firmware update.

Avg. ride time: 9m per week
  • Average ride time is based on Strava activity over the last 3 months. Give your reviews credibility by connecting your account.

consistent & reliable shifting

    i'm running the 6770 on both of my road bikes and i love how effortless the shifting is. no missed shifts, no adjustments for cable stretch/fatigue that often results in chain rattle. i have > 2,500 miles on these derailleurs and they have been very reliable, even in long rainy rides. battery life is sufficient for several months of shifting between charges. micro adjustment makes dialing in various/different cassettes very easy to do, even on the fly. i will never go back to mechanical.