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.
Before you start, to avoid any misunderstanding:
please take the 5 minutes needed to read the compatibility articles use instructions.
If you have any questions (or additions and corrections), please use the BikeGremlin forum’s compatibility section:
https://www.bikegremlin.net/forums/bike-compatibility/
Table Of Contents (T.O.C.):
- Basic terms and what to pay attention to
- Shimano
- SRAM
- Campagnolo
- Rotor’s hydraulic derailleurs
- Table of RD movement ratios for various standards
- Problems preventing you from EVER tuning your derailleurs properly – video
- BikeGremlin’s comment – explanation
TL/DR
Rear derailleurs (RD) are stupid: they just move left-right depending on how much you tighten/release the shifter cable. However, if you pull the shifter cable by 1 mm, some derailleurs will move for about 1 mm, while others will move for about 1.7 mm (with plenty of models in between).
This is called “RD movement ratio.“
Your shifter dictates how much cable is pulled/released by each click.
The trick is:
- Your shifter should match the number of sprockets (speeds) you have.
- Your derailleur movement ratio should match your shifter’s cable pull/release amount.
Otherwise, you can’t tune your derailleur to shift properly with each shifter click.
In this article I’ve explained how RDs work, and listed the movement ratios and which derailleurs are compatible with which shifters – in case you like mix-matching. 🙂
0. 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 (or “derailleur movement 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 (and at least one exotic – by Rotor):
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.
There are a few caveats here. See below, my comment on 10/11 Shimano MTB RDs.
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.
Update: According to Peter’s feedback, it won’t work with Campagnolo.
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! most current models are compatible and will work with Shimano MTB 10-speed RDs in practice.
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.
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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 for 11 speeds, and 1.01 for 12 speeds.
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.
In 2018, Campagnolo introduced their own 12 speed standard – not compatible with any other.
4. Rotor
Rotor’s hydraulic rear derailleurs are only compatible with their hydraulic shifters.
5. Table of RD movement ratios for various standards
The table shows how many mm derailleurs move laterally (left-right – on average across their movement range) per one mm of caple pull or release by the shifter. The smaller the movement ratio – the more cable you need to pull/release to make a gear shift (all else being equal).
| Shimano standard – 1.7 | SRAM 2:1 – 1.7 | Campagnolo old – 1.4 |
| Shimano 10 MTB – 1.2 | SRAM 1:1 – 1.1 | Campagnolo new – 1.5 |
| Shimano 11 road – 1.4 * Including Tiagra 4700 10 speed road | SRAM Exact Actuation – 1.3 | Campagnolo Revolution 11+ – N/A |
| Shimano 11 MTB – 1.1 | SRAM X-Actuation 11-speeds – 1.12 | |
| Shimano Dura Ace 6 to 8 speeds – 1.9 | SRAM X-Actuation 12-speeds – 1.01 |
6. Problems preventing you from EVER tuning your derailleurs properly – video
7. BikeGremlin’s comment – explanation
This was originally posted as a reply to a comment, but there are almost 200 comments to this article now, so I’m moving it here:
Due explanation:
I had managed to get some things working OK, even though they don’t match looking by the manufacturer’s specs.
When it comes to specs, this is what Shimano says:
First they say (said) 9, 10 and 11 are all non-compatible with each other.
Now, on the very same page, they claim otherwise, under 10 speed rear drivetrain compatibility section.
Their Zee (RD-M640-SS), and Saint (RD-M820-SS) RDs are noted as 10 speed only.
While the Deore you noted does say 10/11 speeds.
To make things more interesting (and confusing), Deore 11 speed series has:
RD-M5100-SGS that says 1×11, and RD-M5120-SGS that says 1×10, 2×10, and 2×11.
My goal when writing this series of articles was to help myself, by having all the combos that work (in spite of the manufacturers’ specs. stating otherwise) in one place.
The no-go stuff was written down to help when mix-matching, to know what to rule out from the start.
A problem I face is, even when I make a combo from this no-go zone to work, I can’t say with enough certainty that it works on most bicycles.
Like here, when pairing an 11 speed MTB cassette with an 11 speed road groupset.
For me, it would take at least 5 more bikes, tried and (field) tested to be able to say: 11 speed MTB cassettes work with road 11 speed shifters & RDs, in spite of the obvious and measurable differences in pitch.
The above noted Shimano tech. and product specs. certainly don’t make things less confusing (at least for me).
Also, with so many what/ifs and gotchas (by Shimano), it seems the only thing to do is make a database driven app where you enter your shifter, and cassette models, to get a list of RDs that work with those.
Same goes for other combos (cassette, and RD to get a matching shifter model).
Because stating all the possible combos on one page would make it very, very long and almost unreadable (shifter models x cassettes x RD models… it grows exponentially for each new combo, even if only listing the combos that work).
Bottom line:
Combos that are noted here to work – do work, i.e. I’m yet to find a case when they don’t (poor tuning by the user/mechanic aside, of course).
Combos that are not noted to work – sometimes they work, more or less perfectly. If the differences are slight enough, it’s usually worth giving it a try (as we did with the MTB cassette and 11 speed road shifters, noted above).
Having said all this, I do try to keep this as correct and up-to-date as possible. So will add notes regarding 10/11 MTB RDs (and shifters) in the matching sections/articles. Even if not providing a definite answer.
Related post – Bicycle rear hub compatibility:
Compatibility posts are also available in eBook (printable and Kindle) and paperback editions on Amazon:
If you have any questions (or additions and corrections), please use the BikeGremlin forum’s compatibility section:
https://www.bikegremlin.net/forums/bike-compatibility/
The existing comments (questions and answers) posted to this article over the years have been moved to this BikeGremlin forum thread:
https://www.bikegremlin.net/threads/compatibility-04-rear-derailleurs-article-comments.100/
Thank you for this page !
I’ve found very interesting and I’m looking forward to knowing all the movement ratios, cable pull etc. in order to choose components independently of what manufacturers would want us to do 🙂
I have no measure, but I can confirm that a road 11s Exact Actuation shifter (Apex flatbar) works OK with a “10s” EA MTB RD. I’ve done this on 2 bikes, one with a 11-40 HG 11s cassette (and GX 2×10 RD), and the other with a 10-42 XD 11s one (and X7 2×10 RD).
I just thought that “exact actuation” components were compatible, but it looks that I’ve mistakenly forgotten to take into account different pitches for 11s road and MTB cassettes ?
It can get a bit complicated, that’s for sure. The easiest way for me to comprehend it all is dividing into “logical groups” to put it that way.
Cassette is the most “stupid” component in the whole drivetrain “stack”. It has a number of sprockets and the pitch (distance at which they are lined up relative to each other).
Derailleurs are a little bit “smarter”. Their job is to move left-right when the control cable is pulled-released. The only thing they need to “worry” about is by which amount they will move per (1 mm of) cable pull-release. However, the number of speeds printed on the derailleur is more a marketing thing (to put it simplified, without going into fine details that don’t make much of a difference anyway). Since the number of speeds is not something derailleur needs to “think” about. Hence we come to the next link in the drivetrain chain (pun not intended 🙂 ):
Indexed shifter. The “brains” of the whole operation. It has a bit more complicated job. It needs to pull-release an exactly pre-defined amount of cable per each “click” (shift) to make sure that the derailleur (with its pre-defined movement ratio per 1 mm of cable travel) moves exactly the same amount, to match the cassette’s pitch.
So both the cassette pitch, cassette number of cogs and the derailleur movement ratio are what shifter needs to “have in mind” when doing its job (pulling/releasing the shifter cable).
10 speed road and MTB cassettes, for example, have the same pitch. As long as the shifter is a 10 speed one, it only needs to match the (rear) derailleurs movement ratio and one single pitch and number of cogs.
With 11 speed cassettes, on the other hand, since MTB and road ones have (very slightly) different pitch, in addition to matching the RD movement ratio and the number of cogs, shifter also needs to “know” whether it’s working with road, or a MTB cassette.
This is why 11 speed ExactActuation road and MTB shifters don’t pull/release the same amount of cable per shift.
Having said all this, the difference in 11 speed MTB and road cassette pitch is not very large. Tested with a Shimano drivetrain, 11 speed road shifter and RD combo worked fine with an 11 speed MTB cassette (to my surprise). Haven’t tested this with SRAM though.
Thanks for that 🙂
Yeah, I knew that the “number of speeds” of a derailleur had no technical meaning, it was just marketing. Hence my builds with 11s shifter and so-called “10s” RD’s.
And I also have two other “Frankensteins” : 1st with a Dura-Ace “10s” road RD & 9s SRAM Plasma twister “2:1” and the 2nd with a Gevenalle 10s CX shifter & 9s Hone RD.
I had heard of many builds with 11s MTB cassettes plus road shifter/RD, so I didn’t even considered that the cogs were not spaced the same distance. My bad 🙁 But it works OK !
So that would be so great if 3 tables with data for Cassettes pitches / shifter cable pull / RD ratio could be set up. I know it’s hard work because manufacturers don’t want that their nebulous marketing argumentation could be scratched and reduced in so simple figures 😉
Yes, that’s clear since you had mentioned the “Frankenstein” (like that 🙂 ) builds. The answer was made “more thoroughly” then necessary for two reasons:
1) In case anyone else with a similar dilemma, but less experience, reads it.
2) For my own reference, since I think, as you have suggested, that an article that explains how all that stuff works together, but in a simplified way, needs to be added (still not sure how to put it to not miss anything important, but still not be too complicated).
I’m happy to hear that MTB-road cassette swap works with SRAM as well. 🙂
The suggestion you made is great by the way. Thank you.
For now, I have made tables with all the data (cassette pitch, shifter cable pull etc.) – each post in this Compatibility section has the relevant table.
Combining it all in one table would not look too nice on most screens, but I could make a separate article that has all the tables/charts in one place.
I could start with 3 tables:
– Cassette pitch
– RD movement ratio
– shifter cable pull
All one below the other.
Then add the rest of the tables (chain width comes to mind first).
How does that idea sound?
I don’t know exactly how to show that as simple as possible…
Maybe a table with Shifers standards listed horizontally (or vertically) and RD standards listed vertically (or horizontally), and in the matrix, showing the calculated pitches and the possible matching cassettes standards ? (with colours, for instance to distinguish “official” compatibility and other degrees of compatibility)
That sounds like a perfect candidate for a small database. To pick shifter and derailleur options from a drop-down list, then it would show the closest matching cassettes.
But there is a problem there, most of my data is rounded (up/down) to make it easier to see and refer to.
Table would have to be nicely designed and thought of.
Anyway, this is added to my (rather long 🙁 ) to-do list.
this article and #7 rear shifter gave me the courage to mix the following:
SRAM X0 9s shifter
Taiwan 11-46T 9s cog
shimano deore 10s RD with clutch
worked like a charm
Just wondering, to make use of my very light SRAM X0 9s RD with a 12-36T 9s cog hanging around, can I use a shimano 11-speed rear shifter? it will be for a weight weenie bike build.