In-Depth Guide to Shimano 12-Speed Cassette Compatibility

Key Points for Understanding Shimano 12-Speed Cassette Compatibility

Shimano 12-speed cassette compatibility depends on two main factors:

1. Compatibility with the wheel (freehub body)
2. Compatibility with the derailleur

Only One Shifting Technology

Shimano’s 9- to 11-speed cassettes come in two shifting technologies: “HYPERGLIDE”¹ and “LINKGLIDE”².
However, as of 2024, all Shimano 12-speed drivetrains are available only in the HYPERGLIDE version.

Therefore, unlike 9- to 11-speed systems, you don’t need to worry about shifting technology differences when selecting 12-speed components.

Compatibility with Wheels (Freehub Bodies)

Shimano 12-speed cassettes come in two fitting standards:

1. HYPERGLIDE Road 12-speed: HG Spline L2
2. HYPERGLIDE MTB 12-speed: Micro Spline³

Up to 11-speed, Shimano used HG Spline-type freehub bodies for both road and MTB, allowing some compatibility between the two (e.g., using the same wheels across different gear counts or disciplines).

However, starting with 12-speed:

• Road 12-speed uses: HG Spline-type
• MTB 12-speed uses: Micro Spline-type

These are entirely different standards.

Here’s a table showing compatibility between major Shimano freehub types and 12-speed cassettes:

The “HG Spline L2” standard for road 12-speed cassettes is based on the older “HG Spline L” (used for road 11-speed), but with 18 splines instead of the original number—keeping the shape the same but doubling the spline count.

As a result, wheels with HG Spline L freehub bodies (i.e., Shimano Road 11-speed wheels) are designed to accept HG Spline L2 12-speed cassettes. This works because two cassette splines fit into one spline groove on the freehub.

On the other hand, wheels with HG Spline L2 freehubs cannot accept 11-speed cassettes. The increased number of splines (18) on the freehub body prevents fitting the older cassette type.

All MTB-specific HYPERGLIDE 12-speed cassettes use the Micro Spline standard, meaning they are only compatible with Micro Spline freehub bodies.

In short: Shimano’s 12-speed MTB drivetrains must be used with Micro Spline freehubs and are not compatible with any other standard.

Compatibility with Derailleurs

Road 12-Speed Cassettes Have Separate Models for Di2 and Mechanical

All 12-speed MTB cassettes are mechanical, but for road bikes, DURA-ACE and ULTEGRA are Di2-only, while 105 offers both Di2 and mechanical options, and GRX offers both Di2 and mechanical options.

Be aware that Shimano’s road 12-speed cassettes come in different models depending on whether they are for Di2 or mechanical drivetrains.

Especially for ULTEGRA and 105, the 4-digit model numbers are confusing because the last digit indicates “0 = Di2” and “1 = mechanical”, so be sure to check before purchasing.

Road and MTB Cassettes Are No Longer Interchangeable

Road 12-speed cassettes have a top smallest cog of 11T, same as 11-speed, while MTB 12-speed cassettes use Micro Spline, with a smaller 10T cog.

Also, MTB cassettes are far more focused on ultra-wide gearing compared to 11-speed, whereas road cassettes have made some advancements in range but are not as wide as the MTB 51T cogs.

Therefore, as opposed to before, road and MTB drivetrains cannot share cassettes anymore.

Derailleur Compatibility Is Clear-Cut

While Shimano’s 12-speed drivetrains offer fewer options for sprocket configurations, derailleur options are now more straightforward.

Up to 11-speed, Shimano rear derailleurs came in two cage lengths—“SS” (short cage) and “GS” (medium cage)—and you needed to swap between them depending on the sprocket you were using.

For 12-speed, there are only 6 configuration patterns (3 for road and 3 for MTB), so the choice of derailleur almost directly corresponds to the gearing configuration you choose.

GRX 12-Speed: Enjoy the Middle Ground

As we’ve seen, Shimano’s 12-speed drivetrains no longer offer compatibility between road and MTB cassettes. However, the GRX 12-speed (RX820 series)⁴ takes up the middle ground.

GRX 12-speed comes in the following configurations:

1. 1 x 12 UNBEATABLE (same as MTB 1 x 10-45T)
2. 1 x 12 UNSTOPPABLE (same as MTB 1 x 10-51T)
3. 2 x 12 UNDROPPABLE (same as road 2 x 11-34T, 2 x 11-36T)

The GRX series will allow for customization that combines road and MTB features, making it a perfect option for those looking to enjoy both types of drivetrains.