component-RD-6770-SS

This RD-6770 rear derailleur is a 10-speed rear derailleur and as such it isn't really used anymore. All current and previous Di2 generations have moved on to 1

di2-dealer-manual-ultegra-6770

Ultegra 6770 Dealer Manual

manual-di2-rear-derailleur

Di2 Rear Derailleur User Manual

Has your RD-6770 broken? You cannot *just* replace that with an 11-speed model - all installed derailleurs *must be* the same speed. 

Read more on upgrading your bike and compatibility on the pages linked below.

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

Did you know most 10-speed and 11-speed Di2 hardware is cross-series compatible? You can actually mix different series and even different generations of Di2 hardware, as long as you make sure you follow the Di2 compatibility chart!

Hidden somewhere on the Shimano E-Tube Project website is a [Di2/e-Tube compatibility chart](https://bike.shimano.com/en-EU/e-tube/project/compatibility.html). This useful PDF helps you select your components, making sure they're compatible before spending $$$ and installing them on your bike.

Have a nice Ultegra 6870 setup but want the [newer R8000 shifters](/component/ultegra-dual-control-lever-st-r8050) so that you have [extra buttons on the hoods](/enable-the-buttons-on-your-di2-shifter-hoods)? You can!

Want to use the [mountain bike Di2 display](/component/xt-display-junction-sc-mt800) on your road bike? You can!

Feel like upgrading your derailleurs but not your shifters? Sure! You can!

## 12-speed Di2 compatibility
Before I get started though, a quick note on 12-speed Di2 compatibility. Shimano released their [12-speed DURA-ACE and Ultegra Di2](/dura-ace-r9250-ultegra-r8150-wireless-di2/) groupsets to the world on September 1st, 2021. 

While Shimano has been pretty good with backward compatibility in the past, these new groupsets actually feature *very* limited compatibility with the older Di2 series. There is [a page on 12-speed compatibility](/12-speed-r9200-r8100-and-11-speed-di2-compatibility/), so read that if you're looking for 12-speed Di2 information. 

The remainder of this page applies to 11-speed and 10-speed Di2 compatibility, **not** the newer 12-speed Di2.

## Compatibility chart? Where? How does it work?
The latest version of the compatibility chart can be found on the [Shimano e-Tube project website](https://bike.shimano.com/en-EU/e-tube/project/compatibillity.html). At the time of writing the latest version of the chart is 5.0.1.

Let’s say you want to know whether your [Ultegra RD-6870-GS](/component/ultegra-medium-cage-rear-derailleur-rd-6870-GS) rear derailleur and [Dura-Ace ST-R9150 shifters](/component/dura-ace-dual-control-lever-st-r9150) are compatible with each other. Start with your battery and work your way down.

![Di2 e-tube compatibility - connected boxes](https://assets.bettershifting.com/di2_etube_compatibility_boxes_connected_87eca69a3c.png)

In the image above I have selected the [SM-EW90](/component/below-the-stem-junction-a-sm-ew90) Junction box, [R9150-series Dura-Ace shifters](/component/dura-ace-dual-control-lever-st-r9150) and two 11-speed derailleurs; the [RD-6870 Ultegra rear derailleur](/component/ultegra-medium-cage-rear-derailleur-rd-6870-GS) and the [Ultegra FD-R8050 front derailleur](/component/ultegra-front-derailleur-fd-r8050-f). Note that I could also have selected the [Dura-Ace FD-R9150 front derailleur](/component/dura-ace-front-derailleur-fd-r9150-f) if I wanted to.

Shimano recommends you use components all from the same series, because that’s when they perform best. However, this isn’t feasible for everyone and fortunately, they allow you to use different generation components on the same bike..

The only thing you can never do is mix different speed **derailleurs** or mtb / gravel / road **derailleurs**. **__All derailleurs have to support either 10-speed or 11-speed and from the same ‘category’__**.

### Mixing MTB and Road/GRX components
So.. can you use mountain bike di2 hardware with road hardware? Sort of… it’s complicated. You can definitely use road shifters on a mountain bike – but would you really want to? However, let’s say you wanted to build a 1×11 Di2 setup? You’d probably want to take advantage of the Clutch System Shimano equipped the mountain bike rear derailleurs with, but use your road shifters. You should be able to do this no problem! Alternatively you can use a [GRX rear derailleur](/component/grx-2x-rear-derailleur-rd-rx815) with road shifters, or the [Ultegra RX805 clutch rear derailleur](/component/ultegra-shadow-rd-rear-derailleur-rd-rx805-gs). 

The only real limitation is that derailleurs you use have to be either road/gravel or mountain bike derailleurs – **__you cannot mix these derailleurs__**. Other than that you’re free to do whatever you want.

<LImage width="250" height="250" alt="Alfine MU-S705 motor unit" src="https://assets.bettershifting.com/component_MU_S705_c44237316f.jpeg" />

## E-Bikes, Di2 hubs, motor units
Plenty of people are building Di2 E-Bikes using the [MU-S705](/component/alfine-internal-geared-hub-motor-unit-mu-s705/) or **MU-U500**/**MU-U510** motor units and [Internal Geared Hubs](https://bike.shimano.com/en-EU/product/component/alfine-s7050s705-di2/SG-S7051-11.html). 

While the hubs are Di2-specific, they are not actually connected to the Di2 system. They're just designed to work with the Di2 motor units and can handle the forces the motor units produce.

When it comes to compatibility though, looking up information on these units can be a little confusing. If you look up the hub, you'll find only a couple of entries. 

So what gives? Are the hubs only compatible with Bosch E-Bikes? Are the hubs not compatible with current parts at all?

Don't worry - everything is fine. You see, for compatibility purposes, that hub does not matter at all. **Di2 compatibility** for these systems is **determined by the drive unit**. Ignore the hub, just look at the MU-UR500/510 and the MU-S705 entries instead.

## Compatibility charts
Like you’ve read above, I've linked the Shimano Di2 compatibility charts. Click the image below to view the full compatibility chart PDF. Note that the pages relevant to your setup depend on which series hardware and, perhaps more importantly, which battery or battery mount you’re using.

[![Di2 e-tube compatibility charts image link](https://assets.bettershifting.com/di2_etube_compatibility_charts_link_e9de0203b8.png)](https://bike.shimano.com/content/dam/e-tube/assets/images/contents/project/compatibillity/pdf/en/HM-CC_5.0.1-00-EN.pdf)

featured-di2-etube-compatibility

Di2 Compatibility - mix Ultegra, DURA-ACE, XTR, XT and GRX components

upgrade-smew67a

Upgrade your old 6770 series 10 speed Di2 bike to 11 speed Di2. This guide tells you how to do that and also upgrade to di2 synchronized shifting and improve your bike's looks.

In-depth guide on upgrading your old Di2 bike

<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

thumbnail_derailleur_specs_what_do_they_mean_featured.jpg

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

Ultegra 6770 was Shimano's first Ultegra Di2 groupset. It was launched in 2011 and supports 2x10 speed gearing. 

Short Cage Rear Deraileur (10 speed)

Ultegra RD-6770-SS

Affiliate Links

Specifications

Related components

Related pages

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

Di2 Compatibility - mix Ultegra, DURA-ACE, XTR, XT and GRX components

In-depth guide on upgrading your old Di2 bike

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

Understanding Di2 derailleur specifications

Manuals & other documents