Modified at: Mar 17, 2023
Posted at: Mar 16, 2023
This section summarizes the compatibility of Shimano's sprockets and wheels (free bodies) for MTB, which are a mixture of old and new standards, the latest Micro Spline and the previous HG spline, and what to look out for when purchasing.
Table of contents
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Shimano has two major freebody standards for MTB.
Knowing the difference between them will help you understand Shimano’s MTB sprocket and wheel compatibility.
In the MTB industry, the use of “single-speed front and multiple-speed rear” gears has become a requirement over the past few years in order to cope with more severe changes in road surface conditions.
Since a front single inevitably offers a narrower choice of gear ratios than the traditional front double (front two-speed) or front triple (front three-speed), it is necessary to increase the number of rear gears while widening the gap between the low and top gears.
Thus, at the EUROBIKE show in May 2018, XTR’s M9100 series, the top grade for MTB, was unveiled; with the M9100 series, the rear speed of Shimano’s components for MTB was upgraded from 11 to 12 speeds for the first time.
The new standard for 12-speed MTB components is the Micro Spline.
Since the Micro Spline freebody has more grooves than the conventional HG spline freebody, conventional MTB sprockets for the HG spline cannot be installed. Similarly, it is not possible to install sprockets for Micro Spline on HG spline freehubs. In other words, they are no longer completely compatible.
Currently, all 12-speed Shimano MTB components are Micro Spline compatible, so if you want to use Shimano 12-speed MTB components, you must have a Micro Spline-compatible freehub.
As of 2023, Micro Spline will only be used on Shimano’s 12-speed MTB sprocket models, so keep in mind that “only MTB 12-speed sprockets will have special compatibility.
Incidentally, in 2021, road bike components will also have 12-speed rear sprockets, but these will not use Micro Spline.
HG spline, which stands for Shimano’s high-speed shifting technology “HyperGlide,” has long been used as Shimano’s free body standard not only for MTB but also for road bicycles.
Generally, the term “Shimano free” is used to refer to this HG spline.
All HG spline freebodies have the same number of grooves, but there are several different types of HG spline freebody standards, as they vary in height according to the number of gears.
The following two remain in the current official Shimano compatible sheets
All Shimano 8, 9, and 10-speed sprockets have the same sprocket thickness except for some 10-speed sprockets. (However, there is also a 10-speed-specific freebody, different from HG spline M, that is compatible only with “some 10-speed sprockets”).
For MTB, since compatibility with HG spline M was continued when converting to 11-speed, 11-speed sprockets for MTB can be used with HG spline M free bodies that were used in the 8-, 9-, and 10-speed era.
On the other hand, 11-speed sprockets for road bikes, unlike 11-speed sprockets for MTB, require 11-speed wheels with HG spline L free bodies due to the increased sprocket thickness.
Since the groove design of HG spline L remains the same and the height of the freebody is only increased, a sprocket for HG spline M can be used by inserting a 1.85mm spacer.
Later, when MTBs went to 12-speed, they adopted Micro Spline, but for road 12-speed sprockets, the special specification is compatible with both the conventional HG spline L and the new HG spline 12-speed freebody.
Let’s take a look at which current freebodies are compatible with Shimano’s MTB sprockets and the newly released MTB component CUES sprockets.
| Micro Spline | HG spline M (8, 9, 10 speed, MTB 11 speed free body) |
HG spline L (Road 11, 12 speed free body) |
|
|---|---|---|---|
| MTB 12-speed | ◎ | - | - |
| MTB 11-speed | - | ◎ | ◎(+ 1.85mm spacer) |
| MTB 10-speed | - | ◎ | ◎(+ 1.85mm spacer) |
| MTB 9-speed | - | ◎ | ◎(+ 1.85mm spacer) |
| MTB 8-speed | - | ◎ | ◎(+ 1.85mm spacer) |
| CUES 11-speed | - | ◎ | ◎(+ 1.85mm spacer) |
| CUES 10-speed | - | ◎ | ◎(+ 1.85mm spacer) |
| CUES 9-speed | - | ◎ | ◎(+ 1.85mm spacer) |
Road bike users may think that HG spline M freebodies for 8, 9, and 10 speeds are “old wheel standards,” but HG spline M freebodies are still used in current 11-speed components for MTB.
The CUES, which was just announced in March 2023, is also an HG spline M-based sprocket on Shimano’s official compatibility chart, and is announced to be compatible with both HG spline M and HG spline L. It is also not compatible with Micro Spline.
When using Shimano parts for both sprockets and free bodies, you can combine them as per the compatibility above, but when using third-party wheels and sprockets, you need to be careful because some products are out of sync with the compatibility above.
Occasionally you will see “HG spline compatible 12-speed sprockets for MTB” that do not exist in Shimano’s lineup. Examples include SRAM’s PG-1230 and PG-1210.
Originally, 11-speed sprockets for MTB “solved the height shortage of HG spline M, which was used up to 10-speed sprockets, by pushing it out to the spoke side. The third-party HG spline-compatible 12-speed sprocket on the market seems to achieve 12-speed by “pushing out one more step from the 11-speed sprocket on the spoke side.
To begin with, SRAM’s PG-1230 and PG-1210 are “12-speed sprockets for SRAM Eagle 12-speed components that can be used with Shimano free (HG spline) wheels. Keep in mind that you may encounter some problems when using it with Shimano 12-speed for MTB.
Some third-party manufacturers other than SRAM offer HG spline-compatible 12-speed sprockets that can be used with Shimano components, but some of the cheaper products seem to cause chain drop when the crank is turned backwards, even if the shifting itself is not a problem.
To begin with, sprockets from third-party manufacturers are not compatible with Shimano, so be aware that there is a risk when purchasing them.
With third-party wheels, you may be able to choose the freebody standard of the hub at the time of purchase. The choices in this case are often patterned as follows
Of these, the Shimano HG free body is the one to watch out for.
If the wheel is for MTB, it is likely to be “HG spline M” which is compatible with Shimano’s 8, 9, 10, and 11 speeds for MTB, but if it is for road or gravel, it is more likely to be “HG spline L”.
Even if it is HG spline L, it can be used with a spacer, so it is not that big of a problem.
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