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Bicycle rear derailleur compatibility - which rear shifters, cassettes and chains can it be combined with

Compatibility [04] Rear derailleurs

Updated: 06/10/2019.

This post explains bicycle rear derailleur compatibility, i.e. what derailleurs can work with which number of rear sprockets (cassettes) and which rear shifters. For explanation of other rear derailleur functioning and limitations, such as chain wrap capacity, read this article: Rear derailleur.


Basic terms and what to pay attention to

Most modern bicycles have index shifters, that work with a certain number of clicks. One click per gear change. That is moving the chain from one sprocket/chainring to another with each click.

In order for this to work, these things need to be in tune:

  • Length of cable that shifter pulls/releases with each click. This is called shifter cable pull.
  • Distance that rear derailleur (RD in the remainder of this text) moves laterally per 1 mm of cable movement. This is called rear shift ratio. E.g. if RD moves for 2 mm for 1 mm cable movement (pull or release), then the rear shift ratio is 2.
  • Rear sprocket spacing.

Not directly related to shifter-derailleur compatibility, but it is also crucial to use proper cables and housing. I wrote a post explaining shifter (and brake) cable and housing standards.

When RD compatibility is mentioned, it is all about it’s tune with the shifter cable pull and rear sprocket spacing. When it is all set up correctly, one click of the indexed shifter shifts exactly and correctly one gear (i.e. one sprocket) at the rear. Compatibility will be explained per number of gears and per manufacturer. If it is not noted otherwise, it is understood that shifter make and number of gears match the RD make and the actual number of rear sprockets. There are three major RD and shifter manufacturer standards:

  1. Shimano
  2. SRAM
  3. Campagnolo
  4. Rotor’s hydraulic derailleurs


1. Shimano

6, 7, 8 and 9 speeds

Rear shift ratio is 1.7, that is for 1 mm of cable pull/release, RD is moved left/right by 1.7 mm. Shimano calls this 2:1 ratio for marketing reasons.

All these RDs are compatible and any 6 to 9 speed RD will work perfectly with either 6, 7, 8 or 9 speed shifter. Regardless whether it’s a MTB, or road shifter, or RD. They are also compatible with Shimano 10 speed road shifters, except the Tiagra 4700 series.

Shimano Dura Ace from 1984 to 1996 period (6 to 8 speeds)

Rear shift ratio is 1.9. They are compatible only with Shimano Dura Ace shifters from the same period (that is for 6, 7 and 8 speeds).

10 speed ROAD RD

Rear shift ratio is 1.7, so it’s compatible with all the 6 to 9 speed shifters, as well as road 10 speed shifters. Same rear shift ratio. MTB 10 (and 11 speed) shifters won’t work well.

Exception is Shimano Tiagra 4700 10 speed road RD – it has the same shift ratio as Shimano road 11 speed RDs, so it will work only with Tiagra 4700 shifters and Shimano 11 speed road shifters.

Another exception is the new “gravel” group (with hydraulic brakes): Shimano GRX. Caple pull wise it’s the same as Tiagra 4700.

10 speed MTB RD

Rear shift ratio of this RD is about 1.2. It is only compatible with Shimano 10 speed MTB shifters and nothing else. Shimano calls this system Dyna-Sys.

11 speed ROAD

Rear shift ratio is around 1.4.  Only compatible with Shimano 11 speed road shifters.

The same shift ratio is used for Tiagra 4700 10 speed groupset, so it’s compatible with it as well, but not with other 10 speed road groupsets.

Rear shift ratio of 1.4 matches old Campagnolo ratio, but I haven’t tested this in practice.

11 speed MTB

Rear shift ratio is around 1.1. Compatible with Shimano MTB 11 speed shifters. Shimano calls this system Dyna-Sys, same as 10 speed MTB, but they’re not compatible!

It has similar rear shift ratio to SRAM 1:1 standard (explained later in this post), so it should match it as well, but I haven’t tried it yet!

11 and 12 speed MTB – Hyperglide+ (XTR M9100)

From summer of 2018 Shimano introduces a new Hyperglide+ 11 and 12 speed MTB standard. It comes with a new XTR M9100 rear derailleur, that only works with a matching shifter (which has an integrated 11, or 12 speed operation switch!) and Hyperglide+ 11 and 12 speed cassettes.


2. SRAM

SRAM has four RD families, with 4 different amounts of RD movement per cable movement (actuation ratios). So the only thing to pay attention to is actuation ratio. As long as the RD matches shifter’s actuation ratio (and vice versa), it will work fine.

First, less popular family of SRAM RDs are the ones compatible with Shimano 2:1 standard. Rear shift ratio of 1.7 means they will work with Shimano (and SRAM 2:1) shifters for 6 to 9 speeds (both road and MTB) and road 10 speed ones, except Tiagra 4700 10 speed road shifters.
RDs made in this standard were marketed as 6, 7, 8 and 9 speed models, though this is determined by the shifter – RD doesn’t care how many rear sprockets there are.

Second, more popular SRAM standard is 1:1, with rear shifter ratio of 1.1. This shift ratio is the same as Shimano MTB 11 speed RD (and shifter), so they should be compatible, but I haven’t tested this yet.
RDs made in this standard were marketed as 7, 8 and 9 speed models.

Third, newer standard is Exact Actuation. Rear shifter ratio is 1.3.
Marketed as 10 speed road and MTB , as well as 11 speed road.

Fourth family is X-Actuation, with 1.12 ratio.
Available as 11 and 12 speed MTB RDs 

EDIT: Based on this comment (on this very article) and provided links to SRAM’s website, Exact Actuation and 1:1 are the same thing. Will have to measure, check and confirm this.


3. Campagnolo

Campagnolo has two standards of rear shift ratio. Old 1.4 and new 1.5. Also, not every shifter pulls the same amount of cable with each click. With 10 speed for example, there is more cable pull for “slower” speeds, than there is for the others.  2.5 mm pull five times (from smallest 1st to the 6th sprocket), 3 mm for 7th and 8th, then 3.5 mm for 9th and 10th. 2.83 mm average cable pull per click.  🙂

Apart from that, as of 2014 (don’t take my word for the exact year), campagnolo introduces another 11 speed standard. Previous Revolution 11 and the newest Revolution 11+. They are not compatible.

Since Campagnolo cassettes sprocket spacing differs from other manufacturers’, it is hard to combine Campagnolo RDs with anything but the appropriate Campagnolo shifters and in most cases cassettes too.

Table of rear shift ratios for various standards:

Shimano standard – 1.7SRAM 2:1 – 1.7Campagnolo old – 1.4
Shimano 10 MTB – 1.2SRAM 1:1 – 1.1Campagnolo new – 1.5
Shimano 11 road – 1.4SRAM Exact Actuation – 1.3Campagnolo Revolution 11+ – N/A
Shimano 11 MTB – 1.1SRAM X-Actuation – 1.12 
Shimano Dura Ace 6 to 8 speeds – 1.9  


4. Rotor

Rotor’s hydraulic rear derailleurs are only compatible with their hydraulic shifters.

Related post – Bicycle rear hub compatibility:

Compatibility of bicycle rear hubs - which can accept what kinds of sprockets (cassettes)
Compatibility of bicycle rear hubs – which can accept what kinds of “sprockets” (cassettes)

Compatibility posts are also available in eBook (printable and Kindle) and paperback editions on Amazon:

Bicycle Drivetrain Compatibility on Amazon
Bicycle Drivetrain Compatibility on Amazon
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64 thoughts on “Compatibility [04] Rear derailleurs”

  1. Relja,
    I truly value this most helpful response which makes total sense and I understand. Thank you too for the suggestion about swapping the RD & cassette. Once I’ve settled on final positioning of the brake levers & bled the systems I’ll get started on the back end & shifter.

    Reply
    • MTB and road FDs generally aren’t a 1-1 match. In practice, it depends on your riding conditions, your preferences and criteria. While it might not work just perfectly, shift as fast and as accurately as possible, I’ve had quite satisfying results mix-matching those. This especially goes for double (as in not-triple) chainring cranks. There, FD movement has 2 basic positions, that can be limited using the limit screws. So it’s easier to set it up to works satisfactory.

  2. Thanks, was thinking of converting my road bike w/ drop bars to flat bar, I have a Sora 9 speed at rear and triple crankset w/ Sora FD at front, just want to know if Alivio shifters would be compatible as front & rear shifters.

    Reply
  3. My Mt bike was 10 speed XT shim shifter with 11 speed XTR RD. So how did that work when the 10s pull is 1.2 and the 11s 1.1? All I did was a straight swap between 10s RD and 11s R.

    Reply
    • I can only guess it is close enough to not cause problems – while shifting might not be perfectly fast and precise, it is, apparently, good enough. Here’s a video of another miss-match that works OK in practice:

      https://www.youtube.com/watch?v=TCmQZzeH_aU

      Which components are you using now (rear shifter, RD, cassette and the chain)?

  4. this is amazing. best article ive read on the issue. straight to the point. thank you so much

    Reply
  5. I have a RD SRAM APEX exact actuation with Sram apex 1x brifter.
    Now, I want to change my setup into flatbar. What shifter i need to, if with :
    1. 10 speed cassette
    2. 11 speed cassette

    *hard to find sram apex 1x shifter in my place.

    Reply
    • 1. SRAM Exact Actuation 10 speed shifter should work, either MTB or Road type.
      2. Same as 1, except the shifter must be 11 speed. The problem with that, however, is that I don’t know of any SRAM Exact Actuation 11 speed MTB shifters – only road.

    • Yes, and it’s all compatible with 11 speed road derailleurs as well.

      Old 10 speed cable pull, even for road (i.e. not muddy) riding conditions just wasn’t precise enough, too little cable pulled per shift.

      With MTB 10 speed they went for more cable pull right away (though not the same ratio as for road and this new gravel groupsets).

  6. SRAM Exact Actuation is actually 1:1 as stated by SRAM on their web site on almost all EA RD products.
    Just a few examples:

    MTB RD 9s,10s
    https://www.sram.com/en/sram/models/rd-x7-a1
    MTB RD 10s
    https://www.sram.com/en/sram/models/rd-gx-t21-a1
    ROAD RD 10s
    https://www.sram.com/en/sram/models/rd-apx-a1
    ROAD RD 11s
    https://www.sram.com/en/sram/models/rd-riv-b1

    From one of their product description page…don’t remember exactly which one:

    Technologies

    1:1®
    1:1 Actuation is superior by design. Every unit of cable you pull moves the derailleur the same amount. Actuation stays precise and fluid slogging through mud, bouncing off rocks, rutting through roots wherever you find yourself, whatever conditions you’re in. It’s dependable. Tolerant. Easiest to set up. Easiest to adjust. And, not coincidentally, the top choice of the top MTB riders. Got it? Good.

    Exact Actuation™
    When we launched our road technology from scratch we reapplied our MTB proven SRAM 1:1 actuation ratio (shifter cable travel : derailleur movement) for 10 speed rear shifting. EA helps to simplify/stabilize the uneasy act of balancing rear derailleur hanger design, tight cog spacing and exact cable tension. The result: the easiest index shifting system to set up and it stays that way.

    I can’t find any 1.3 pull ratio SRAM RD…it seems that Exact Actuation is just some marketing BS for their medium / high end 1:1 RD (non eagle X-actuation)

    Reply
    • Looks that way from those links. The problem is the exact actuation (pun not intended) ratio numbers have always been very hard for me to find – goes for Shimano and Campagnolo as well.
      Thank you for taking the time and pointing this out.
      I will measure to confirm the next time I get a hold of SRAM groupset (pretty exotic commodity in Serbia, Shimano is 99.9 % of the available and used equipment).

  7. Regarding SRAM EA pull ratio (and EA shifters cable pull):

    some simple math:
    pull ratio x shifter pull = cassette pitch

    SRAM 10s MTB EA
    1.3 x 3.1 = 4.03
    1.1 x 3.1 = 3.41
    should be 3.95, so both 1.3 and 1.1 pull ratio are wrong or (most likely) your shifter cable pull data is wrong

    SRAM 11s Road EA
    1.3 x 3.1 = 4.03
    1.1 x 3.1 = 3.41
    should be 3.74

    And ,by the way ….(as you can notice) you just CAN’T HAVE same RD pull ratio AND shifter cable pull for different pitch casette

    my best guess is both have 1.1 pull ratio and your shifter cable pull data is wrong

    3.95 : 1.1 = 3.591 (3.6 must be the correct EA 10s MTB shifter cable pull )
    PS: can be tested with a shimano 10S MTB shifter (3.6 cable pull) and the 10s EA SRAM RD

    3.74 : 1.1 = 3.4 ( 3.4 must be the correct EA 11s ROAD shifter cable pull)
    PS: can be tested with a shimano 11S MTB shifter (3.4 cable pull) and the 11s EA SRAM RD

    What do you think ?

    Reply
    • Derailleur movement ratio per 1 mm of cable pull is one set variable.
      Shifter is designed to match that, based on the cassette pitch.
      I believe it is (implicitly, if no other way) explained in the articles on shifter and derailleur compatibility.

      With known either derailleur movement ratio, or shifter’s cable pull per click (preferably measured across 5 or more clicks to minimize measurement errors), and cassette’s pitch, the other can be calculated (shifter’s cable pull per click, or derailleur movement ratio).

      To make things more interesting, even when using manufacturer’s data (when available), when added to the formula, doesn’t align 100% (perhaps intentionally, since top and low derailleur position is limited by limit screws, not sure).

      So, for me at least, the safest method is to double check using some samples.
      Which I will do the first time I get a hold of SRAM groupset again.

      With a few notes:
      – Derailleur has movement ratio (relative to cable movement), while shifters have cable pull (per shift). That is how I would define it to avoid confusion (it’s complicated enough already 🙂 ).
      – The figures for cable pull and RD movement ratio are rounded in most instances.

      The latter note still doesn’t get close enough to work with both 10 and 11 speed. It is an obvious mistake.
      I’ll have to take the time and double check the data definitely – well noticed and noted. The mistake is most probably with SRAM Exact Actuation road shifter cable pull. Still, as I like to say “one good measurement is better than a 1000 expert opinions”, this calls for re-measuring to check and confirm.

      P.S. This kind of feedback is invaluable – in order to make all the info as accurate as possible. Thank you very much for taking the time and pointing it out.

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