DURA-ACE RD-R9150 Short cage rear derailleur

component-RD-R9150

The Shimano DURA-ACE Shadow Rear Derailleur is an 11-speed derailleur that features synchronized shift and a low-profile (Shadow) rear derailleur design.



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DURA-ACE R9150 Dealer Manual

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Di2 Rear Derailleur User Manual

It allows for ergonomic shifting operation without stress, race endurance for less damage in crash and maintains compact and smooth appearance.

The short cage **total capacity** is 33 teeth, with a **low sprocket range** of 30T-25T and a **top sprocket range **of 14T-11T. The **max front difference **is 16 teeth.

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!


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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

Do you have smaller hands than most and do you find the brake levers on your Shimano bike a bit hard to operate? Or are your hands relatively large? 

Don't worry, you can easily change the lever reach and bring the brake levers closer - or move them further away.

You can change your lever reach on all Di2 levers, and it generally works the same for non-Di2 Shimano levers.  All you need is a **2mm hex key**. 

Note that the *reach* is sometimes also referred to as *lever stroke*, especially in older Shimano documentation.

## Change rim brake Di2 lever reach
Since the process is slightly different for rim brake levers and hydraulic disc brake levers, I've split this page up into two small sections. This section describes how to change the reach on the rim brake [ST-6770](/component/ultegra-10-speed-dual-control-lever-st-6770/), [ST-6870](/component/ultegra-dual-control-lever-st-6870/), [ST-R8050](/component/ultegra-dual-control-lever-st-r8050/), [ST-R8150](/component/ultegra-rim-brake-wired-dual-control-lever-st-r8150/), [ST-9070](/component/dura-ace-dual-control-lever-st-9070/), [ST-R9150](/component/dura-ace-dual-control-lever-st-r9150/), and [ST-R9250](/component/dura-ace-rim-brake-wired-dual-control-lever-st-r9250/) levers.

Changing the lever reach (or stroke) on the rim brake levers is easy enough. The first thing you do is pull back the cover to expose the adjustment bolt.

![Pull hood cover to back](https://assets.bettershifting.com/pull_back_from_front_f6bd95de5c.png)

Next, take your **2mm** hex wrench. 

![ST-6870 adjusting](https://assets.bettershifting.com/st_6870_adjust_reach_7ba57f32d9.jpg)

Turn **left** or **counterclockwise** to move the lever outward, or **increase** the reach. This will effectively move the lever further away from the handlebar.

Turn **right** or **clockwise** to move the lever in, or **decrease** the reach. This moves the lever closer, making it easier to grab.

On my Ultegra 6870 lever, the full range of motion (adjustability?) looks like this:

![ST-6870 reach adjustment range](https://assets.bettershifting.com/st_6870_reach_range_ec3b2eee0b.gif)

## Change disc brake Di2 lever reach
This section applies to the hydraulic disc Di2 shift levers: [ST-R785](/component/non-series-hydraulic-disc-brake-lever-st-r785/), [ST-R8070](/component/ultegra-hydraulic-disc-brake-lever-st-r8070/), [ST-R8170](/component/ultegra-disc-brake-wireless-dual-control-lever-st-r8170/), [ST-R9170](/component/dura-ace-hydraulic-disc-brake-dual-control-lever-st-r9170/), [ST-R9270](/component/dura-ace-disc-brake-wireless-dual-control-lever-st-r9270/), and the GRX [ST-RX815](/component/grx-hydraulic-disc-brake-lever-st-rx815/). 

Shimano's hydraulic disc levers have both a *reach* and a *free stroke* adjustment. 

Changing the *reach* will affect how close the brake lever is to the handlebar, while the *free stroke* changes the amount of travel before the brake pads hit the rotor. 

This page is on changing the reach only, but there are plenty of videos on setting up the free stroke on [YouTube](https://youtube.com). Note that if you change the free stroke, that'll also change the initial lever position - and you may need to change your reach afterward as well.

This video by [Rides of Japan](https://www.youtube.com/@ridesofjapan) explains it well:

<YouTube videoId="9TkudgYe0EY" />

### Change reach on R8070, R9170, R7170, R8170, and R9270
Setting up the shifter reach on [ST-R8070](/component/ultegra-hydraulic-disc-brake-lever-st-r8070/), [ST-R8170](/component/ultegra-disc-brake-wireless-dual-control-lever-st-r8170/), [ST-R9170](/component/dura-ace-hydraulic-disc-brake-dual-control-lever-st-r9170/), and [ST-R9270](/component/dura-ace-disc-brake-wireless-dual-control-lever-st-r9270/) is easy - you don't even have to move the lever cover.

The adjustment bolt for the **reach** is on the inside of the lever itself, as shown in the **left** half of this image:

![ST-R8070 reach adjust photo](https://assets.bettershifting.com/st_r8070_reach_adjust_d1ebcb28b1.jpg)
(the bolt shown on the right is the **free stroke** adjustment bolt)  
  
Turning the bolt clockwise increases the lever reach, while turning it counterclockwise decreases the reach. 

![ST-R8070 reach adjustability](https://assets.bettershifting.com/st_r8070_adjust_range_ee7dfb120c.gif)

### Lever reach on ST-R785 and ST-RX815
In order to change the reach on these levers, you'll have to pull back the hood cover as shown below.

![Pull hood cover to back](https://assets.bettershifting.com/pull_back_from_front_f6bd95de5c.png)

Next, locate the reach adjustment bolt. On ST-RX815 it is located on top of the lever:

![ST-RX815 lever reach bolt](https://assets.bettershifting.com/st_rx815_lever_reach_bolt_81bc618914.png)

Turn clockwise to decrease lever reach. Turn anticlockwise to increase the reach, or move the lever away from the handlebar. Use a **2mm** hex wrench.

The ST-R785 lever reach adjustment bolt works the same as the others - turn clockwise to increase the reach, and turn counterclockwise to decrease it. Note that you'll have to use a flat-head screwdriver.

![ST-R785 adjust bolt image](https://assets.bettershifting.com/st_r785_reach_adjust_screw_92b60346a7.png)

## Question, comments, suggestions
That's it! You should now be able to set up the reach as you like. 

Are things unclear, or are you missing something? Please let me know! You can [send me a message](/contact/), or leave a comment below.

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Do you have small hands? Or extra large hands? Read this page to figure out how to change your Shimano Di2 shift lever (or shifter) reach.

Change your Di2 lever free stroke and reach

<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).

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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

<NewContentAlert title="Updated content available" text="An improved page on Synchronized Shift has been published. I'm not taking this older page down any time soon, but recommend you read the new guide on Synchronized Shift" link="/di2-synchronized-shifting-the-complete-guide/" link_text="Read the Complete Guide on Synchronized Shift" />

When Shimano introduced the Dura-Ace R9150 series in 2016 they also released Synchro Shift. Then, a few months later, they made Synchronized Shifting available for Ultegra 6800 and Dura-Ace 9000 users as well. 

All you need is up-to-date firmware and the current generation battery, the [BT-DN110](/component/internal-battery-bt-dn110).

## Synchronized Shifting requirements
Synchronized shift is available to users running current or previous generation Ultegra or DURA-ACE Di2 and a current-generation battery. This means you need one of the following series Di2 to run synchro-shift:

- Ultegra 6870
- Ultegra R8050
- DURA-ACE R9000
- DURA-ACE R915
- XT M8050
- XTR M9050
- GRX

You will also need the [BT-DN110 battery](/component/internal-battery-bt-dn110) or [BM-DN100 external battery mount](/component/external-battery-mount-bm-dn100).

*On mountain bikes the same battery requirements apply, but you’ll also need one of [SC-M9050](/component/xtr-display-junction-sc-m9050), [SC-M9051](/component/xtr-display-junction-sc-m9051) or [SC-MT800](/component/xt-display-junction-sc-mt800) in order to use synchronized shift*. You can use mountain synchronized shift on bikes equipped with either XTR M9050 or XT M8050.

## What is Synchro Shift?
According to Shimano; “*Synchronized Shift is a function that automatically shifts the front derailleur when the rear derailleur is shifted, allowing the derailleurs to work together efficiently*.” This means that you would never manually have to shift the front derailleur anymore. The system will do it for you when it thinks the time is right.

### Shift modes
These are the shift modes you can set up:

- Full Synchro Shift: your front derailleur will shift by itself when it has to
- Semi Synchro Shift: when you shift the front derailleur, the rear derailleur will also shift in order to compensate
- No Synchro Shift / turned off: No automatic shifts will happen. Full manual mode.

![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*

## How to set up Synchro Shift
First you’ll need to download the e-Tube Project software. [Connect your bike to your computer](/how-to-connect-your-di2-system-to-your-windows-computer) using either the [SM-BCR2 (charger)](/component/internal-battery-charger-sm-bcr2) or the [SM-PCE02 (linkage device/diagnostic tool)](/component/pc-linkage-diagnostics-tool-sm-pce02) and start the [E-Tube Software](https://e-tubeproject.shimano.com). You can now customise the shifting settings using these steps:

- Select your bicycle type
- Do the connection check
- Click ‘Customize’
- Click ‘Shift mode settings

![Synchronized Shift setup in etube](https://assets.bettershifting.com/synchro_explained_setup_etube_d037970df7.jpeg)

On this screen, you can select the number of teeth on your front chainring, select the range on your cassette, set gear position control, shift interval and the shift modes.

When riding your bike you can use three different shift modes. Shift mode 1, shift mode 2, and full manual. These shift mode 1 and shift mode 2 are set up as ‘semi-synchro’ and (full) synchro by default. However, you can set them up however you like. You could for example set both shift modes to full synchro, but have the automatic shift points differ for each mode. I'll talk you through customising the different shift modes in another post.

## Change shifting modes on the bike
So you’ve got two custom and one full manual shift modes available – how do you use them? That’s easy! Just double press the button on either your Frame/Bar-end junction box or the below-the-stem junction box and you’ll change modes. In the video below reader Paul Teeter demonstrates how to cycle through the different shift modes.

<YouTube videoId="dHg-Kaj0kJc" />

This is what each light means:

- 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)

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

 Looking for more information on Synchro Shift? Check out the other posts or [the Shimano e-Tube website](https://bike.shimano.com/en-EU/e-tube/project.html). Another good place to start is [GPLama's youtube channel](https://www.youtube.com/playlist?list=PLeDc5AkDnMO9s-hjnba_X7ICg2SPUIgM0):

<YouTube videoId="Z-IuDe7Jklo" />


featured-synchro-explained

Current and previous Shimano Di2 road, mtb and gravel (grx) groupsets feature Synchronized Shifting. Learn what it is, how to set it up and tweak it.

Di2 Synchro shift – how does it work?

Released in 2016, the Shimano R9150 (rim brake) and R9170 are described by Shimano as system engineering at its peak. Each of the components magnifies the qualities of the others for an unparalleled level of performance. Optimizing input to maximize output. That’s how it achieves supremacy.

Short Cage Shadow Rear Derailleur

DURA-ACE RD-R9150-SS

Affiliate Links

Specifications

Related components

Related pages

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

Change your Di2 lever free stroke and reach

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

Understanding Di2 derailleur specifications

Di2 Synchro shift – how does it work?

Manuals & other documents