An 11-speed SRAM cassette can be used with a Shimano derailleur when one of the following conditions is met:
1. The user combines a Shimano 11-speed MTB Derailleur with an 11-speed SRAM X-Actuation shifter and an 11-speed SRAM or Shimano MTB cassette.
2. The user relies on a friction shifter to control the rear derailleur.
Understanding Index Shifting
To learn why sometimes there’s an incompatibility between cassettes and rear derailleurs, it’s necessary to become familiar with the term index shifting.
The movement of modern bicycle shifters is segregated into clicks. Each click indicates a shift that moves the chain up or down the rear cassette.
For a shift to be performed, the shifter has to pull (upshift) or release (downshift) a certain amount of gear cable. In the case of indexed drivetrains, that amount is predetermined to make shifting faster and worry-free.
However, having a pre-determined cable pull/releas gh. The movement of the rear derailleur has to be predetermined too. Otherwise, the derailleur will not move to a controlled location every time a shift is initiated.
To achieve that, rear derailleurs have a rear shift ratio.
The rear shift ratio indicates how much the derailleur moves per 1mm of cable pulled or released by the shifter.
For instance, if the rear shift ratio is 1:1.3, the derailleur will move 1.3mm per 1mm of cable pulled or release by the shifter.
Requirements For Compatability Between a Derailleur and a Shifter
In an indexed drivetrain, a rear derailleur has to meet the following criteria to be compatible with a shifter:
- Sufficient max. cog capacity. The derailleur has to be capable of comfortably reaching the largest cog on the cassette. If the derailleur has a short cage, it won’t be compatible with large cogs such as 42T.
- Correct rear shift ratio for the cassette. If the rear shift ratio of the new derailleur doesn’t match that of the original derailleur designed for the cassette in question, the shifting experience will be poor due to inaccurate derailleur movement.
If the rear shift ratio is smaller, the derailleur will be unable to move the chain enough for a full shift to occur.
If the rear shift ratio is notably larger, the derailleur will overshift.
Combining an 11-speed SRAM Cassette With a Shimano Derailleur
There are two types of 11-speed SRAM derailleurs:
- SRAM Exact Actuation (Road Bikes)
- SRAM X-Actuation (Mountain Bikes)
The rear shift ratio of SRAM Exact Actuation is 1.3 whereas that of X-Actuation is 1.12.
There isn’t a Shimano derailleur that has a matching rear shift ratio. However, Shimano’s 11-speed MTB derailleurs have a 1.1 rear shift ratio.
For that reason, people have reported decent success when combining Shimano’s 11-speed MTB derailleurs with 11-speed SRAM cassettes.
Calculating The Inaccuracies
It’s possible to calculate how much a derailleur moves per shift if you know the cable pull of the shifter and the rear shift ratio of the derailleur.
Derailleur Travel = Cable Pull x Rear Shift Ratio
The data that we need is in the table below:
(11-speed SRAM models)
|Rear Shift Ratio
|Derailleur Travel Per 1 Click/Shift (also cog pitch)
|SRAM Exact Actuation
|Shimano 11-speed MTB
|Shimano 11-speed MTB
In the first column, we have the derailleur models.
The second column contains the cable pull of SRAM’s 11-speed road and MTB shifters.
The Shimano derailleur is present two times because there are two possible SRAM shifters. Please note that the second column doesn’t use the Shimano cable pull.
The third column shows the rear shift ratio of the respective derailleur.
The final column indicates the derailleur travel per 1 shift.
It’s also important to note the derailleur travel is equal to the cog pitch. The cog pitch is the center-to-center distance between two adjacent cogs.
Conclusion: An 11-speed Shimano MTB derailleur can be used with an 11-speed SRAM MTB cassette and an 11-speed SRAM MTB shifter.
The rear shift ratio of 11-speed Shimano MTB derailleurs extremely close to that of SRAM models and thus result in minimal discrepancies in derailleur movement per 1 click – 3.92mm (SRAM) vs. 3.85mm (Shimano). This is a 1.82% percentage difference.
Even in the case of indexed shifters, 1.82% are not expected to result in notable shifting issues.
FAQ: Can I use an 11-speed Shimano Road derailleur too?
The rear shift ratio of 11-speed Shimano road derailleurs is 1.4. It’s close to the rear shift ratio of SRAM’s Exact Actuation derailleurs (1.3), but the discrepancy is large enough to result in over-shifting when using an SRAM shifter. Thus, it’s recommended to avoid this combination.
Friction Shifters Always Work
The problems described above apply only to indexed drivetrains. If you’re relying on a friction shifter, you will be able to use any derailleur that can cover the entire cassette.
Unlike index shifters, friction shifters are “free”. It’s up to the rider to determine the position of the shifter and there are no clicks. The movement of the shifter from one end to the other is smooth.
Consequently, the rear shift ratio of the derailleur becomes irrelevant because the rider can always compensate by moving the shifter’s lever a little in the necessary direction for a shift to occur.
Indexed shifting was initiated in 1984 with the introduction of SIS (Shimano Index Shifting) as part of the 6-speed Dura-ace groupset. But before then, riders were relying on friction shifters for both the front and rear derailleur.
Eventually, the rear shifter became indexed whereas the front one was kept in friction mode for a little longer because it was cheaper that way and the user could easily “trim” the front derailleur to avoid rubbing of the chain against the front derailleur’s cage.
Of course, friction shifters have a major downside – they can’t match the speed of indexed drivetrains no matter how hard you train. For that reason, they are no longer popular. But if you don’t care about speed, they still have their place on “alternative” machines.
Frequently Asked Questions
FAQ: What is the range of 11-speed SRAM cassettes?
11-speed SRAM cassettes are available in the following gradations:
The smaller the largest cog, the smoother the transitions between the gears are. Smoother transitions allow the rider to maintain a higher cadence (rotations of the cranks per minute) which in return results in a higher average speed.
If you plan on using the largest cassette (11-42), the 11-speed MTB Shimano derailleurs that fit the criteria are:
- GRX RD-RX812
- RD-M4120 10/11
- GRX RD-RX817