Upgrading your 9/10/11-speed drivetrain to 1x12.

The fairly recent crop of 1x12 drivetrains promises to deliver new levels of performance and a much higher range (more on that later), coupled with the decreased complexity and weight of a 1x drivetrain. There are several other benefits, especially when compared to 3x9 or 2x11 drivetrains.

When Shimano introduced its 12-speed drivetrains they introduced a new freehub standard called MICRO SPLINE. Shimano’s previous HG Standard has been the cornerstone of road and mountain bike drivetrains for decades, both Shimano’s as well as SRAM’s before SRAM introduced their XD driver. The HG freehub remained largely unchanged over many years and supported cassettes with 8 to 11 cogs. This was possible by squeezing increasingly more cogs into the same space by moving them close together and making the chains narrower.

Shimano MICRO SPLINE & HG Standard freehub bodies, side-by-side

But why couldn’t Shimano just continue to squeeze more cogs onto the HG freehub? The issue has to do with the smallest 10T cog on all the new Shimano 12-speed drivetrains, which allows for a whopping 510% range. However, this new 10T cog is too small to fit onto the Standard HG freehub body. In order to accommodate the new 10T cog, the new MICRO SPLINE freehub body is actually shorter than an HG freehub body. This allows the smallest 10T cog to be attached not to the freehub body itself, but the 12T cog which is the last cog that mounts to the freehub body. The 10T cog then mounts inside the 12T cog and is held in place with a series of splines that match up with a series of grooves in the 12T cog.

MICRO SPLINE cassette 10T & 12T cogs

Two smallest cogs, MICRO SPLINE vs. HG Standard

Now let’s try to bring this all back to the topic of actually upgrading your older 9/10/11-speed drivetrain to 1x12. With the new MICRO SPLINE an upgrade can become a lot more complicated because you’d need an entire new wheel with a MICRO SPLINE hub, or a new MICRO SPLINE hub with which you can rebuild a wheel. Both of these options can be quite expensive. In rare cases you may be able to upgrade your hub with a MICRO SPLINE freehub body, but this is especially unlikely if you have an older drivetrain with an older rear hub.

Not all is lost though, as there are some very interesting options that do allow you to upgrade to a 12-speed drivetrain without having to replace the rear wheel or hub. SunRace makes a series of 12-speed 11-51T cassettes that fit onto the HG Standard freehub bodies and are compatible with all Shimano 12-speed derailleurs and chains. The main difference is that the smallest cog on the SunRace cassettes is 11T vs. 10T on the Shimano cassettes. We’ve put together a multitude of upgrade kits which include these SunRace 12-speed 11-51T cassettes, ranging from Deore 12s M6100 to XT M8100. They make for a very cost effective and frictionless way to upgrade your bike to a 1x12 drivetrain.  

You can check out our selection of these HG Compatible upgrade kits HERE. 

How do you know if one of these kits will be compatible with your drivetrain?

Even if you have a much older 9-speed cassette on your bike, as long as the smallest cog on it is 11T, one of our HG Compatible groupsets with the SunRace 12-speed 11-51T cassette will fit and be a great upgrade option.