component-RD-6870-GS

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 28

di2-dealer-manual-ultegra-6870

Ultegra 6870 Dealer Manual

manual-di2-rear-derailleur

Di2 Rear Derailleur User Manual

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](/frequently-asked-questions/i-had-a-crash-and-my-rear-derailleur-stopped-working-how-do-i-reset-it/).

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](/di2-synchronized-shifting-the-complete-guide/).

The installation method for the [RD-R8050](/component/ultegra-short-cage-shadow-rear-derailleur-rd-r8050-ss/) / [RD-R9150](/component/dura-ace-short-cage-shadow-rear-derailleur-rd-r9150-ss/) / [RD-6870](/component/ultegra-short-cage-rear-derailleur-rd-6870-ss/) and [RD-9070](/component/dura-ace-short-cage-rear-derailleur-rd-9070-ss/) rear derailleurs is similar to that of traditional road rear derailleurs, but setting the limits and indexing is slightly different. You first index the rear derailleur and only then set the top and low limits.  

If your rear derailleur has a clutch mechanism then you're probably looking for this installation guide: [RD-RX805 / RX-RX815 / RX-RX817 installation guide](/rd-rx805-rd-rx815-rd-rx817-di2-rear-derailleur-installation-guide/).

### Torque wrench
While you can get away with using standard hex wrenches if you absolutely have to, I always use my torque wrench when installing expensive bike parts. There is more information on the required torque for each part in this [Shimano Torque Chart](https://assets.bettershifting.com/Shimano_DM_TORQUE_02_ENG_4ed1b89643.pdf).

## Mount the derailleur to the frame
The RD-R8050 and RD-R9150 derailleurs are direct mount ready and come with a ***B2-link plate***. Whether or not you need to use this depends on the rear derailleur mount on your frame. Generally, direct mounts are in line with the seat stay, while a standard mount will make a sharper bend down. The image below should help you identify the mount on your frame:

![direct mount vs standard mount](https://assets.bettershifting.com/rd_rx_installation_guide_rear_derailleur_direct_vs_standard_mount_ea968de92d.png)

## Standard mount - RD-R8050 / RD-R9150
On a standard mount frame you install the derailleur with the ***B2-link plate*** attached. It should come this way out of the box. If the ***B2-link plate*** is not installed, do so now – it is colored green in the image above.

Apply a small amount of grease to the mounting bolt and secure the rear derailleur to the frame. Before tightening it fully, make sure the stopper plate touches the B-tension stop, with no gap between them. 

**IMPORTANT**. You may be tempted to install the derailleur hanger B-tension stop between the stopper plate and the *other* plate. Don't. **Make sure the B-tension stop touches the stopper plate** with no gap in-between, as shown in the image below.  I've coloured them yellow and blue respectively.

![RD-R8050 / RD-R9150 / RD-6870 / RD-9070 stopper plate](https://assets.bettershifting.com/install_rd_r8050_r9150_9070_6870_3c4bb29b86.png)

### RD-6870 / RD-9070 Rear derailleurs
Easy! Simply screw the derailleur attachment screw into the mount. The recommended torque is 8-10Nm.  The end result should look similar to the image above - except there is only one tab on the derailleur - the stopper tab (coloured blue).

## Direct mount - RD-R8050 / RD-R9150
Is your frame equipped with a direct rear derailleur mount? Then remove the ***B2-link*** from the rear derailleur so that you can mount it directly onto the frame. You do this by removing the bracket axle using a **size 5 hex wrench**. Remove the link and attach the derailleur to the frame using the bracket axle.

![RD-R8050 / RD-R9150 B2-link](https://assets.bettershifting.com/install_rd_r8050_r9150_9070_6870_b2_link_05f3eb9a85.png)

## Connect the electric wire
If you haven’t run the [EW-SD50 electric wire](/component/di2-electric-wire-ew-sd50/) to the rear derailleur yet, do so now. Now use the Di2 plug tool to push the electric wire into the connector. Push firmly until you feel (and possibly hear) it click into the socket.

## Set the end adjustment screw
Now first make sure the rest of the system is installed and that you can shift both derailleurs. The next step is to set the end adjustment screw (or ***b-screw***). This will set the angle of the rear derailleur and change the distance between the guide pulley and chain on the cassette.

Shift the front derailleur to the smallest chainring and the rear derailleur to the largest sprocket. Use a **size 2 hex wrench** to turn the adjustment screw and move the guide pulley as close to the sprocket as possible but not so close that the chain gets jammed.

![RD set the b-screw](https://assets.bettershifting.com/rd_rx_installation_guide_rear_derailleur_b_screw_fe8007ba6b.png)

Shimano hasn't published any information on the recommended distance between the guide pulley and the sprockets for 11-speed Di2, but this is what they say in the 12-speed documentation:

- **11-28T** cassette: 18mm
- **11-30T** cassette: 14mm
- **11-32T** cassette: 10mm
- **11-34T** cassette: 6mm

Now shift to the smallest sprocket and make sure the chain does not get jammed. If there is any slack in the chain in this gear use the adjustment bolt to eliminate this slack.

## Micro-adjust the rear derailleur
Before setting the high/low limit screws you will have to micro-adjust or index the rear derailleur. Note that this is different from how you would set up mechanical rear derailleur – there you would set the limit screws first and then do indexing.

![RD adjustment 5th sprocket](https://assets.bettershifting.com/rd_rx_installation_guide_cassette_fifth_sprocket_5f128c1c9c.png)

- Shift the front derailleur to the small chainring.
- Shift the rear derailleur to the fifth sprocket.
- Press and hold the button on your junction box until the red LED illuminates, indicating you’re in adjustment mode.

You can now adjust the position of the rear derailleur using the shift buttons:

![RD adjustment switch X](https://assets.bettershifting.com/rd_rx_installation_guide_rear_derailleur_adjustment_x_7dfaf6a18e.png)

- Press the [**X**] button while also turning the crank to move the guide pulley towards the 4th sprocket.
- Keep doing this until the chain makes contact with the 4th gear and a subtle noise is heard.
- Note that while you are in adjustment mode the guide pulley will overrun slightly and then move back a bit. When checking the position of the guide pulley and gear, make sure the derailleur has come to a stop.

![RD Adjustment Y switch](https://assets.bettershifting.com/rd_rx_installation_guide_rear_derailleur_adjustment_y_7c8b459555.png)

Now press the [**Y**] switch five times in order to move the guide pulley five steps back towards the smallest sprockets. The rear derailleur should be indexed now. This will be the starting point for all future adjustments.

To leave adjustment mode just press and hold the button on the junction box until the LED turns off and you will leave adjustment mode.

Use both the front and rear derailleur to shift through all the gears, making sure no chain rub occurs in any of them. If it does, go back to adjustment mode to tweak the rear derailleur indexing.

## Set the low/high stopper bolts
Adjusting the low/high stopper bolts is a relatively easy affair. Let’s first set the low stopper bolt.

- Shift the rear derailleur to the **largest sprocket** (easiest gear).
- Now use a **size 2 hex wrench** to tighten the low side stopper bolt until it just touches the low side stopper. This is the bolt with an **L** next to it.

Confused? This image should clarify things a bit: If not, just leave a comment or [send me a message](/contact/)

![RD low limit stopper bolt](https://assets.bettershifting.com/adjust_road_rd_low_limit_stopper_bolt_b96bc9cf6b.png)

To check whether your limit setting is correct, shift the rear derailleur down three gears and then back to the largest sprocket again. It should shift to the easiest gear just fine.

### High stopper / top limit
Now we’ll set the high or top side stopper bolt.

- Shift the rear derailleur to the **smallest sprocket** or hardest gear.
- Tighten the top stopper bolt with a **size 2 hex wrench** until it just touches the top-side stopper. This is the bolt with an **H** next to it.
- Turn the top-side stopper bolt counterclockwise one turn to loosen it and allow for the rear derailleur to overshift.

![RD stopper bolt](https://assets.bettershifting.com/rd_rx_installation_guide_low_top_side_stopper_bolt_rear_derailleur_cca353bee7.png)

Note that if you overtighten either stopper bolt the derailleur will not stay in that highest or lowest gear and shift back within five seconds. When this is the case you'll also hear some clicking or ticking, indicating that the derailleur is blocked from fully completing the shift.

Also, according to Shimano, one of the following could happen:

- Chain noise does not stop.
- The battery level drops quickly because extra load is being placed on the motor.
- The motor may be damaged due to overload (irreparable).

Need some extra guidance? I think this video describes the process rather well:

<YouTube videoId="HIvsY4AtQpI" />

## All done!
Your rear derailleur should now be installed and set up pretty well. If you're having problems however, just leave a comment or [send me a message](/contact/) and I'll do my best to help you!


featured-adjust-road-rd

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.

Installation Guide: 10-speed and 11-speed Di2 road Rear Derailleur

**Synchronized shift** is available on all 11-speed and 12-speed road series, as well as MTB and GRX.

That includes:

- 105 R7150 (**12-speed**)
- Ultegra 6870 (11-speed)
- Ultegra R8050 (11-speed)
- Ultegra R8150 (**12-speed**)
- Dura-Ace 9070 (11-speed)
- Dura-Ace R9150 (11-speed)
- Dura-Ace R9250 (**12-speed**)
- XT M8050 (MTB, 11-speed)
- XTR M9050 (MTB, 11-speed)
- GRX RX815 (Gravel, 11-speed)

12-speed Shimano e-MTBs also feature Auto Shift and Free Shift, and I'll cover that in a future article.

In this guide I’ll first explain what *Synchronized Shift* is *exactly*, then walk you through the requirements, and finally, set it up using both [the mobile app](/set-up-di2-synchronized-shifting-using-e-tube-mobile/) and [E-Tube Project for Windows](/di2-e-tube-software-and-downloads/).

Are you wondering why **synchronized shift doesn't work on your 12-speed bike**? Or perhaps your 12-speed time-trial bike? You probably haven't changed the bike's selected shift mode to synchronized shift yet. [Read this section on how to change shift mode](#changeshiftmode).

If you want to skip ahead, use these links:

- [What is Synchronized Shift](#whatissynchroshift)
- [Synchronized Shifting requirements](#synchrorequirements)
- [Change shift mode - enable synchro shift](#changeshiftmode)
- [Set up Synchronized Shift using E-Tube Project for Windows](#setupwindows)
- [Using the E-Tube mobile app to set up Synchronized Shift](#setupmobile)
- [What to do when your cassette/chainrings are not listed](#cassetteisnotlisted)
- [Synchro Shift with FD-6870 / FD-9070](#note68709070synchro)

## What is Synchronized Shift {#whatissynchroshift}
Di2 Synchronized Shift is Shimano’s name for the Di2 automatic shift modes. Yep.. modes. 
There isn’t just one Synchro Shift, but actually two distinct modes, *Full Synchronized Shift* and *Semi Synchronized Shift*. 

According to Shimano; “*(full) Synchronized Shift is a function that automatically shifts the front derailleur when the rear derailleur is shifted, allowing the derailleurs to work together efficiently.*” 

When the other mode - *Semi Synchro Shift* -  is selected, the bike will shift the rear derailleur automatically when you shift the front derailleur. In this mode, the bike compensates for the front shift by moving the rear derailleur one or two gears.

Of course, you can also decide not to use the Synchro modes at all. That is referred to as *Manual mode* - because, as you might have guessed, you’ll be shifting everything manually.

Let’s briefly run through each Synchro mode.

### Synchro Shift (default: S2)
So, knowing that *(full) Synchronized Shift* automatically shifts the front derailleur, how does that work exactly?

Some people think the bike keeps track of your speed and cadence and automatically shifts for you. Others think there is some other kind of intelligence at play.

This would be amazing, but *Synchro Shift* is not that clever. It just automatically shifts the front derailleur when the rear derailleur reaches certain predefined gears. These shift points can be set and fully customized by the user as we’ll discuss below. 

![Synchronized shift map](https://assets.bettershifting.com/synchro_explained_map_d54fc16cc8.png)

When shifting from **11T** towards **28T** the system will automatically shift from the big ring to the small ring between **25T** and **21T**

You can still shift the front derailleur manually any time you like, of course. Note that when you shift the front derailleur yourself it will not shift the rear derailleur to compensate.

### Semi Synchro Shift (default: S1)
When your bike is set to Semi Synchro that means it’ll automatically shift the rear derailleur to compensate for any front derailleur shift. This will reduce or even eliminate big jumps in gear ratios when shifting the front derailleur.

<YouTube videoId="CiYJBhG6QrE" />

It won’t shift the front derailleur automatically, but some people actually prefer *Semi Synchro*. Personally, I went back and forth between *full* and *semi synchro*, then used semi exclusively for about six months and then finally settled on *Full Synchro Shift*.

Switching modes is easy though, so just experiment and see what’s right for you.  
([more on switching modes right here](#changeshiftmode))

### Manual Mode (M)
I know I said there are two synchro modes, but technically this is not a synchro mode at all. In manual mode, the bike doesn’t shift for you at all. It is all about full manual control, just like you’re used to.

<OnPageAd variant="storefront" />

## Synchronized Shifting requirements {#synchrorequirements}
Sounds good? All **12-speed** bikes come with synchronized shift out of the box:

- Ultegra R8100 (12-speed)
- DURA-ACE R9200 (12-speed)
- 105 R7150 (12-speed)

Is yours an **11-speed road bike**? All you need in order to use synchronized shift is the [BT-DN110 internal battery](/component/internal-battery-bt-dn110/) or the [BM-DN100 external battery mount](/component/external-battery-mount-bm-dn100/). Ultegra R8050 and Dura-Ace R9150 bikes generally come with this battery. Older bikes (6870 and 9070) do not.

Synchro shift will work on these 11-speed road Di2 series:

- Ultegra 6870
- DURA-ACE 9070
- Ultegra R8050
- DURA-ACE R9150
- GRX RX815

### Mountain Bikes
Mountain bikes (M8050 and M9050) have been able to run *synchronized shifting* for a while now. The requirements are slightly different. 

A display ([SC-MT800](/component/xt-display-junction-sc-mt800/), [SC-M9051](/component/xtr-display-junction-sc-m9051/) or [SC-M9050](/component/xtr-display-junction-sc-m9050/)) is required and, depending on the display, a specific battery. Any of the combinations below enable *Synchronized Shift* on MTB.

![MTB Synchro shift requirements](https://assets.bettershifting.com/synchro_shift_guide_mtb_table_7552fd526e.png)

## Change Shift Mode - enable synchro shift {#changeshiftmode}
Reading all of the above, chances are pretty good that your bike can do *synchro shifts*. For Ultegra R8050, Dura-Ace R9150, GRX, and newer this will be set up for you out of the box. The older series Di2 may require a [firmware update](/learn-how-to-update-your-di2-component-firmware/) first.

So how do you actually perform synchro shifts? 

Simple - you **switch** your bike to the shift mode you like and then just shift. That’s it.

How? By double-pressing the main function button. 

On **11-speed bikes** you'll find this button next to the **charge port**. 

On **12-speed bikes** the function button is **on the rear derailleur**.

Pressing this button twice will cycle through the three shift modes. The default mode configuration is as follows:

- **Mode M** - Full manual shifting
- **Mode S1** - Semi Synchro shift
- **Mode S2** - Full Synchro shift

I say default configuration because these **S1** and **S2** modes are fully customisable. You can set them up any way you see fit.

You could for example set both shift modes to full synchro, but have the automatic shift points differ for each mode. Or set both modes to semi-synchro, or mix things up a bit.

### What shift mode are you in?
Let’s go back to that button. Knowing that double pressing the function button will change the selected shift mode, how can you tell what mode you’re in?

The LEDs next to the function button will tell you. On 11-speed Di2 these LEDs are on the main junction, while 12-speed Di2 has the LED on the **rear derailleur**. The LEDs light up differently depending on the selected mode.

![Change synchronized shift mode using buttons](https://assets.bettershifting.com/synchro_explained_buttons_6a1a0c4777.png)

#### 11-speed Di2 synchro shift LEDs
- **Solid red/green** lights: manual shift mode
- **Twice blinking red/green** lights: shift mode 1 (default: semi-synchronized shift)
- **Three-times blinking red/green** lights: shift mode 2 (default: synchronized shift)

#### 12-speed Di2 synchro shift LEDs
- **Blue (2 seconds)**: Manual shift
- **Flashing blue (2 times)**: Shift mode 1
- **Flashing blue (3 times)**: Shift mode 2

<YouTube videoId="dHg-Kaj0kJc" />

## Set up Synchro Shift using E-Tube Project for Windows {#setupwindows}
If you haven’t already, download and install [E-Tube Project for Windows](/di2-e-tube-software-and-downloads/). After installing it, [connect your bike to your computer](/how-to-connect-your-di2-system-to-your-windows-computer/) and launch the program.

Once connected click the *Synchronized Shift* button under **Gear Shifting** on the **Customize** tab. 

![This is where you get started setting up synchro](https://assets.bettershifting.com/synchro_shift_guide_start_screen_948df76658.jpg)

You’ll now see the basic setup screen where you can change:

- **FC**: The installed Front Chain rings
- **CS**: The installed cassette
- **Synchronized Shift Interval**: How quickly synchro shifts happen
- **Gear Position Control**: whether or not Gear Position Control is enabled.

Click **Next** and you’ll be shown the shift mode setup screen. 

![Synchronized Shift setup screen](https://assets.bettershifting.com/synchro_shift_guide_synchro_screen_eccd1ee6ac.jpg)

On this page, you can set up both Shift **mode 1** and Shift **mode 2**. 

Directly behind the **S1** and **S2** labels you’ll see the current setting for that mode. In the image below **S1** is set to *Semi-synchronized shift* and **S2** is set to *Synchronized shift*. You can change these simply by selecting the preferred mode from the list.

![Change synchro mode](https://assets.bettershifting.com/synchro_shift_guide_change_mode_41549b3eb6.jpg)

I’ll leave these to the defaults to avoid confusing new users, but feel free to play around with it to see what happens.

### Customise Semi-synchronized shift
Configuring *Semi Synchronized shift* isn’t hard, you just need to know what it is you’re changing. You can change two values: **Rear up on front down** and **Rear down on front up**. 

These do exactly what they say they do.. they change the number of gears the rear derailleur shifts up/down when you shift the front derailleur up/down.

![Semi-synchro settings](https://assets.bettershifting.com/synchro_shift_guide_semi_synchro_d70d0c0219.jpg)

Shifting up means shifting to a harder gear, while shifting down refers to an easier gear.

You can use this to compensate for front derailleur shifts, basically making the jump in gear ratio smaller.


### Set up (full) Synchronized shift
The *(full) Synchronized Shift* settings may look a bit more intimidating, but they’re fairly straightforward. All you do is drag the white boxes to your desired position.

If this seems a bit cryptic, don’t worry. Let’s walk through changing the upshift. On my bike that means shifting from the **39T** to the **53T**.

![synchro shift upshift before](https://assets.bettershifting.com/synchro_shift_guide_upshift_before_b0b724dd94.png)

Starting at the 28T at the top left, follow the green line all the way to the right, to the white box (gear ratio 3.0.0 or **39T**x**13T**). When you shift the rear derailleur one more time it’ll move to the **19T** and also shift the front derailleur. The resulting gear is **53T**x**19T**, with a gear ratio of 2.79.

If you follow the gear ratios closely you can see that, as you shift up, you move through the following gear ratios:

2.29 (**17T**), 2.60 (**15T**), 2.79 (**14T**), 3.00 (**13T**) and then back to 2.79 (**19T**). This last step means that the bike shifts to an easier gear, even though you have been shifting to harder gears for a while.

Let’s change that now.

Doing so isn’t hard, you simply drag the lower white box to the preferred gear / gear ratio. In this example I’m setting it up to shift from gear ratios **2.79** to **3.00** and then to **3.12**. 

![synchro shift upshift after](https://assets.bettershifting.com/synchro_shift_guide_upshift_after_9f116a9d37.png)

Of course you could also select gear ratio **3.53**, that’s up to you. Personally, I like the jump in gear ratio to be relatively small when shifting up, but this is highly personal.

#### Synchronized Downshift
When setting up the downshifts you basically repeat the above process, but this time follow the blue line from the lower right to the top left.

This bike is set to a bit of an extreme downshift. When in the big ring it’ll shift all the way to the last gear, the **28T**. It’ll then shift the front derailleur to the little ring and the rear derailleur to **25T**. This is pretty severe cross-chaining, so let’s fix that.

![synchro shift downshift before](https://assets.bettershifting.com/synchro_shift_guide_downshift_before_509d620c51.png)

I’ll set it up to shift the front derailleur when the rear derailleur reaches the **21T**, or the fourth gear from the bottom. The most sensible gear to shift to seems to be the **17T**, resulting in a shift from gear ratio **2.52** to **2.29**. 

In this scenario, you’re shifting to an easier gear and you’re most likely climbing - or having a hard time at least. You could therefore also decide to jump to the next gear instead, from **2.52** to **2.05**. Take the time to experiment and settle on what works for you.

![synchro shift downshift after](https://assets.bettershifting.com/synchro_shift_guide_downshift_after_77f2b408a2.png)

When you’re happy with the settings just click the Apply button at the bottom left of the window. And don’t forget to disconnect E-Tube Project when you’re done with the app.

## Set up Synchro Shift using the mobile app (Android/iOS) {#setupmobile}
If you have a [D-Fly, Wireless Unit or Display installed](/wireless-unit-di2-display-why-get-a-d-fly/) on your bike then you can also use the mobile app to set up *Synchronized Shifting*. The process is very similar to the one described above, with subtle differences.

For example, the mobile app features some pretty cool animations displaying how the bike moves through gears. It also allows you to set multiple presets and select the ones you like. 

This is pretty cool, but it also means the mobile app can be a bit intimidating and confusing. I have written a separate page on [setting up synchronized shifting using E-Tube Project for mobile](/set-up-di2-synchronized-shifting-using-e-tube-mobile/), so read up all on configuring synchro shift there.

## What to do when your cassette/chainrings are not listed {#cassetteisnotlisted}
If you’ve installed a 105 series or non-shimano cassette or chainring you will have noticed that you cannot select that cassette in the E-Tube app. You cannot tell your bike the exact gearing that is installed and you cannot insert custom cassettes/chainrings.

The only cassettes and chainrings you can select in E-Tube Project are the ones that match the Di2 series currently installed on the bike. Have you built a bike with different series components? The rear derailleur determines what cassettes you’ll be able to select.

Seeing as setting up *(full) Synchro Shift* is done by telling the system to shift from certain gears to other gears you can imagine that not being able to actually select your gears can be a problem.

So what can you do when you cannot select your installed cassette or rings?

***Select the closest match***.

Why? Well, there are a couple of reasons. 
First of all, the selected cassette / chainrings influence the displayed gears and gear ratios on the Synchro setup screen.Also, Gear Position Control is automatically enabled or disabled depending on the selected gearing.

Selecting the closest match will result in a displayed gear ratio that is pretty close to your actual gear ratios. In fact, in most cases it will not be off at all. 

Even if a gear’s number of teeth or gear ratio is wrong, you can still set up synchronized shift. The trick is to look at the gear’s index.

Basically, if you set it up to synchro shift when the rear derailleur reaches the 3rd gear from the top, it’ll always do that - no matter what cassette is installed. 

## Synchro Shift with FD-6870 and FD-9070 {#note68709070synchro}
*Synchronized shift* works on the older 6870 and 9070 series too - after you [install the required firmware updates](/learn-how-to-update-your-di2-component-firmware/). It makes sense for this *Synchro Shift* to be just like that on the newer series. All it really does it shift one derailleur instead of the other at certain points on the cassette, right?

Well...

There are some strange limitations in setting up your *(full) Synchronized Shift* when using the [FD-6870](/component/ultegra-front-derailleur-fd-6870-f/) / [FD-9070](/component/dura-ace-front-derailleur-fd-9070-f/) that go away when using a newer Front Derailleur. 

Specifically: the point at which the bike shifts from the big to small ring can only be set to the last two sprockets or cogs on the cassette.

![Synchro shift 6870 vs r8050](https://assets.bettershifting.com/upgrade_synchro_information_cd5fb81f8b.png)

Those white boxes under the **50T**/**Top** column are the gears you can move the light blue coloured box to - this is the gear at which the bike will shift from the big to small ring. As you can tell from the image, this limitation is only there when using FD-6870 (or FD-9070). When you use [FD-R9150](/component/dura-ace-front-derailleur-fd-r9150-f/) or [FD-R8050](/component/ultegra-front-derailleur-fd-r8050-f/), you can choose the shift point from a much wider range of gears.

This actually put me off using *Synchro Shift* on my 6870 bike for a while and I switched to *semi-synchro*. After a while I switched back to *(full) Synchro* and learned to live with its limitations. Whether or not this works for you is ultimately up to you, but it's good to know.

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## Questions? Comments?
Did you manage to set up your synchronized shifting? Do you have any questions? [Let me know](/contact/) or post a comment below.

If you're looking for roughly the same content in video form, have a look at [GPLama's Di2 playlist](https://www.youtube.com/playlist?list=PLeDc5AkDnMO9s-hjnba_X7ICg2SPUIgM0).

<YouTube videoId="Z-IuDe7Jklo" />

large_synchro-shift-guide-synchro-screen.jpg

medium_synchro-shift-guide-synchro-screen.jpg

small_synchro-shift-guide-synchro-screen.jpg

thumbnail_synchro-shift-guide-synchro-screen.jpg

synchro-shift-guide-synchro-screen.jpg

Synchronized Shifting - what is it exactly? What does it do and how can you set it up? Read the complete guide on synchronized shifting right here. This page will guide you through the process of setting synchro up.

Synchronized Shifting - the complete guide

<NewContentAlert title="12-speed Di2? Go here" text="If you're trying to set up your 12-speed Di2 rear derailleur, use my updated guide." link="/installation-guide/adjust-12-speed-di2-rear-derailleur-shifting-and-limits/" link_text="12-speed Di2 rear derailleur guide" />

Is your rear derailleur not shifting as smoothly as it should? Or maybe you’ve recently learned how to micro-adjust your front derailleur and want to know how to do the same with your road bike rear derailleur? Read on and I'll explain how to make small but effective adjustments to your rear derailleur.

If the term *micro-adjust* seems a bit strange to you, it is essentially the same as *indexing* a derailleur - something you might have done before with mechanical groupsets.

### Limit screws first?
You may be used to setting up your limit screws before doing any micro-adjustment, but the Shimano manual states that for Di2, it is the other way around. First, do micro-adjustment fine-tuning, and then set up your limit screws. 

Don't worry if you have already set up the limit screws, just know that if you are setting up a derailleur from scratch, you don't necessarily need to set the limits first.

Tip: If your bike has been set up properly you can skip setting the pulley distance and limits, and follow only the steps mentioned under **Adjustment Mode**.

## Check guide pulley distance
According to the [Shimano documentation](/learn-how-to-use-the-shimano-documentation/) the first step is adjusting the guide pulley distance. 

![RD adjustment from behind](https://assets.bettershifting.com/adjust_road_rd_pulley_adjustment_bf2c752ce2.png)

- Shift to the largest sprocket of the cassette
- Turn the end adjust bolt to move the guide pulley as close to the sprocket as possible but not so close that the chain gets jammed
- Shift to the smallest sprocket and check the chain doesn’t get jammed on that end of the cassette either
- If there’s any slack in the chain when the chain is mounted on the smallest chainring and smallest sprocket, adjust the end adjust bolt to eliminate this slack

## Adjustment mode
In order to make adjustments to your rear derailleur, you’ll have to enter adjustment mode. When you’re in this mode the shift buttons will only make adjustments – they won’t let you change gears. This is how it’s done:

![RD adjust fifth sprocket](https://assets.bettershifting.com/adjust_road_rd_rear_5th_sprocket_5ebd0a1a4a.png)

- Shift the front derailleur to the small chainring.
- Shift the rear derailleur to the 5th largest sprocket.
- Press and hold the button on your junction box until the red LED illuminates, indicating you’re in adjustment mode.

Easy, right? Now you can micro-adjust your rear derailleur using the buttons on the shift lever:

![RD button direction](https://assets.bettershifting.com/adjust_road_rd_buttons_58967c43ed.png)

- Press shifting button **X** to move the rear derailleur **one step** towards the inside (larger sprocket)
- While turning the crank/front chainring keep moving the rear derailleur towards the **4th largest** sprocket until it makes a slight noise
- The chain now touches the **4th** sprocket. Press the **Y** button four times to move the rear derailleur **4 steps back** (towards the 11T).
- Press the junction box button until the red LED turns off. You have now left adjustment mode.
- Now is the time to make any adjustments to your high/low limit screws – if you need to.

## Set the high/low end stopper bolts
These bolts limit the range of the rear derailleur, meaning it won’t shift to positions that don’t contain a sprocket. Note that Di2 stopper bolts are different from normal stopper bolts. The Di2 derailleurs slightly ‘overshift’ and then move the derailleur cage back in a. This is intentional, but requires you to set up the adjustment bolts a bit less restrictive than you’d do with a mechanical setup.

If your adjustment bolts are over-tightened you might experience:

- Gears do not shift to the top/low gear or shift back by one gear after about 5 seconds
- Noise that doesn’t stop
- The battery level drops quickly due to extra load being placed on the motor
- The motor may be damaged. (irreparable)

## Low stopper bolt

![RD low stopper bolt](https://assets.bettershifting.com/adjust_road_rd_low_stopper_bolt_252a340c8e.png)

Shift the rear derailleur to the **largest** sprocket (easiest gear) and then tighten the low stopper bolt until it just touches the left link (of the rear derailleur). 

If this seems a bit cryptic: it’ll become clear once you’re doing it – don’t worry. The image below shows what to look for when adjusting the Low stopper bolt. You should be able to figure out the High bolt from this.

![RD low limit stopper bolt](https://assets.bettershifting.com/adjust_road_rd_low_limit_stopper_bolt_b96bc9cf6b.png)

Then shift the rear derailleur down three gears and then back to the largest sprocket again. It should shift to the easiest gear just fine.

If it doesn't and you hear a clicking or ticking sound, or if it shifts back within five seconds, relax the limit screw a bit. Don't unscrew it too much though - you don't want the chain to fall off between cassette and spokes.

## Top/high stopper bolt

![RD high stopper bolt](https://assets.bettershifting.com/adjust_road_rd_high_stopper_bolt_4ea0adcef3.png)

Next set up your high stopper bolt. Shift to the **smallest sprocket** and then tighten the adjustment bolt until it touches the left link at the position where the rear derailleur stops.

Then, turn the bolt counter-clockwise to loosen it **one full turn** to allow the rear derailleur to ‘*over-shift*’. (when it shifts, the derailleur will move slightly past its final position and then move back)

This video describes the process rather well:

<YouTube videoId="HIvsY4AtQpI" />

## All done!
Your rear derailleur should be set up perfectly now. Of course, you can always enter adjustment mode again and make small changes but this should be your baseline setup.

Note that while you could do the entire process on the bike, it’s probably best to do it with the bike on a bike repair stand. This will allow you to notice when the chain is touching the 4th sprocket more easily.

The amount of steps you can make differs per hardware series (33 total for 6870, 25 for 9070). If you want to know the number of steps available please have a look at your series’ dealer manual. Alternatively, [connect your bike to your Windows computer](/how-to-connect-your-di2-system-to-your-windows-computer/) and use the e-Tube project software to look up the current setting and available steps.

You can also adjust your [XTR Di2 and XT Di2 mountain bike rear derailleurs](/how-to-adjust-your-mountain-bike-di2-rear-derailleur). Read more on that [right here](/how-to-adjust-your-mountain-bike-di2-rear-derailleur).

featured-gear-position-control

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.

Micro-adjust your 10-speed and 11-speed road bike Di2 rear derailleur

When deciding what derailleur to buy, most people will just look at the largest sprocket/cog they can fit, and make a decision based on that.

This works fine for most of us, but Shimano list **a lot** of other specifications. Why do they do this, and what do the specifications mean?

What is a rear derailleur's **total capacity**, really? Why is there a **top sprocket minimum**?  

And what about front derailleurs? **Chain line**, **total capacity**, **Top gear teeth**?

I'll explain all of these, and why they matter. If you're interested in one of these in particular, feel free to skip ahead:

**Front derailleur**
- [Chain line](#frontchainline)
- [Total capacity](#fronttotalcapacity)
- [Top gear teeth](#fronttopgearteeth)

**Rear derailleur**
- [Top sprocket min/max](#reartopminmax)
- [Low sprocket min/max](#rearlowminmax)
- [Total capacity](#reartotalcapacity) 
- [Derailleur hanger extenders](#hangerextenders)
- [Swapping derailleur cages](#swapderailleurcage)

## Front derailleur
Shimano Di2 road groupsets come with just in front derailleur version, so there's not much to choose there. Are you running Ultegra Di2? Then you'll probably use the Ultegra front derailleur. Is your bike equipped with DURA-ACE? Then it'll have a DURA-ACE front derailleur.

Nonetheless, these still have specifications like **total capacity**, **chain line**, and **top gear teeth**. Let's discuss what these mean.

### Chain line {#frontchainline}
A bicycle's chain line is the **distance** (in mm) between the frame's center and the point right between the two chain rings. 

Shimano **10-speed and 11-speed road** front derailleurs have been designed with a **43.5mm** chain line in mind. Their **12-speed road** front derailleurs were designed for a **44.5mm** chain line. 

The chain line for Shimano's **gravel Di2** groupset (GRX) is **47mm**, and the **MTB** chain line is even more - **48.8mm** and **51.8mm**.

If you find the midpoint between the two rings a bit hard to measure, then just measure the distance from the frame center to each chain ring, and then average that.

A specific crankset will have a **chain line** specification as well, and you can use this to determine whether or not a front derailleur and crankset will work together. 

While some mismatch can be accounted for using [adjustment and setting the limits](/installation-guides/), you cannot turn a 43.5mm chain line front derailleur into a 51.8mm one. 

### Front derailleur Total capacity {#fronttotalcapacity}
The **total capacity** specification of a front derailleur indicates the maximum difference (in teeth) between the largest and smallest chain ring that the derailleur can handle. 

You don't need to take the installed cassette or rear derailleur into account. 

### Front derailleur Top gear teeth {#fronttopgearteeth}
You'll usually see a couple of numbers listed here - this is the range of sizes of large chainrings compatible with the front derailleur. For example, [FD-R8050](/component/ultegra-front-derailleur-fd-r8050-f/) has a **top gear teeth** spec of **46T-53T**, meaning that it is designed to handle large rings sized **46T**, **53T**, and anything in-between.

## Rear derailleur

### Top sprocket min and max {#reartopminmax}
When talking about Shimano derailleurs and **top** sprocket, this refers to the smallest sprocket, or simply the 'hardest' gear. While going outside the specified range will not likely damage your derailleur, it usually results in poor shifting, and *can* lead to a skipping chain.

### Low sprocket min and max {#rearlowminmax}
The low sprocket is the easiest gear, or the largest sprocket (or cog). Most people will pay attention to only the *max* specified sprocket size, but there is a minimum too.

Again, running a cassette with a low sprocket that is smaller than the minimum will generally not damage the derailleur, but it *can* affect shift performance. 

Exceeding the low sprocket **max** is definitely a lot riskier. Go over too far and you'll experience difficulty shifting into the easier gears, and run the risk of damaging your derailleur, wheel, chain, and frame. 

### Rear derailleur Total capacity {#reartotalcapacity}
The rear derailleur total capacity spec is often overlooked, but it is in fact pretty important. It is the maximum amount of chain slack a derailleur can take up or let out, expressed in a number of sprocket teeth. Exceed the total capacity, and your chain will likely be too long or too short for some combinations of gears.

When you exceed a derailleur's total capacity and you shift to the smallest chainring and smallest sprocket, you'll find that the chain is longer than it should be. This can cause chain suck and skipping chains, or worse.

Depending on how you sized the chain, it'll likely be a bit on the short side in the largest chainring - largest sprocket gear. This can make shifting into the bigger sprockets difficult, and your chain might even get stuck.

And yeah, I do realise that this will only be a problem at either end of the cassette - so it's usually fine to exceed the total capacity if you're riding a single event like the Marmotte - but do try to stick to the total capacity for your day-to-day gearing though.

#### Determine a bike's capacity
To determine the capacity you need for a cassette and chainrings combination, take the differences between the largest and smallest sprockets, and the smallest and largest chainrings. The rear derailleur's total capacity must be greater than or equal to the sum of these two numbers.

Basically:

Required RD total capacity >= (Large front ring - small front ring) + (Largest cassette sprocket - smallest cassette sprocket)

So if you have an **11-28** cassette installed and a **50x34** crankset, the total capacity required would be **17** + **16** = **33T**.

Looking at the [Ultegra RD-R8050-SS](/component/ultegra-short-cage-shadow-rear-derailleur-rd-r8050-ss/), this has a total capacity of **33T**, and the low sprocket max it supports is **30T**. You can probably see why it doesn't support a **32T max sprocket** - it simply doesn't have the total capacity to do so.

## Wolftooth and other derailleur hanger extenders {#hangerextenders}
Looking for a way to increase your rear derailleur's max (low) sprocket, or simply the largest sprocket your derailleur can clear? Then you can use a derailleur hanger extender.

These increase the low sprocket max, but **do not** increase a derailleur's total capacity. This makes them ideal for 1x setups since those aren't usually limited by total capacity as much. 

Add a front derailleur though, and it's a whole other story. Sure, a derailleur hanger extender will move the derailleur further away from the cassette and will let the guide pulley do its job... but you'll easily exceed your rear derailleur's total capacity.

Wolf Tooth mention this on their [RoadLink page](https://www.wolftoothcomponents.com/products/roadlink) too:

> RoadLink repositions your derailleur to provide clearance for larger cassette cogs but it does not increase derailleur capacity. It is critical to find and understand your derailleur’s capacity before attempting to expand its gear range.

## Swapping out a rear derailleur's cage {#swapderailleurcage}
Shimano's 12-speed rear derailleurs, the [RD-R9250](/component/dura-ace-shadow-rear-derailleur-rd-r9250/) and [RD-R8150](/component/ultegra-shadow-rear-derailleur-rd-r8150/) only come in one size - there's no short/medium cage for you to choose from.

However, previous generation derailleurs came in different versions - a short cage version (**SS**) and a medium cage (**GS**) one. Some users swapped out the short SS cage for a longer GS cage, in order to fit larger cassettes. 

![RD-R8050-GS and RD-R8050-SS](https://assets.bettershifting.com/r8050_gs_ss_5690cccfd6.png)

This works to some extent, however: modern derailleurs are not just defined by their cages. There are also subtle differences in the derailleur body and parallelogram. 

## More on derailleurs, and chain sizing
That concludes this little page on derailleur limits. I appreciate that this probably doesn't answer all your questions - this page will get updated as time passes. 

I'd love to hear your feedback and questions, so don't hesitate to send them in. Either via the comments section below, or the [contact form](/contact/).

small_derailleur_specs_what_do_they_mean_featured.jpg

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derailleur_specs_what_do_they_mean_featured.jpg

Shimano front derailleur and rear derailleur specifications... what do they mean, really? This page explains all of them, and why they matter. I'll also briefly talk about derailleur hanger extenders and swapping derailleur cages.

Understanding Di2 derailleur specifications

The 6870 Di2 groupset was released in 2013 and is “pro-proven” as it is a direct trickle down from Shimano’s DURA-ACE group. It stands for state-of-the-art technology, proven in pro races, the technology used in ULTEGRA 6800 series with 11-speed, advanced designed brakes, latest chain treatment and more.

Medium Cage Rear Derailleur

Ultegra RD-6870-GS

Affiliate Links

Specifications

Related components

Related pages

Installation Guide: 10-speed and 11-speed Di2 road Rear Derailleur

Synchronized Shifting - the complete guide

Micro-adjust your 10-speed and 11-speed road bike Di2 rear derailleur

Understanding Di2 derailleur specifications

Manuals & other documents