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 3x or 2x drivetrains.

When Shimano and SRAM introduced their 12-speed drivetrains they introduced new freehub standards. Shimano introduced MICRO SPLINE, SRAM their XD freehub driver. 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 they introduced their respective new drivers. 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 and SRAM just continue to squeeze more cogs onto the HG freehub? Technically they could, but in a quest for bigger gear ranges they needed to fit a smaller 10T cog onto the new cassettes which would allow for those larger ranges of 510% (Shimano) and 520% (SRAM). 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 and XD freehub bodies are actually shorter than an HG freehub body. In Shimano's case 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 and XD free hubs an upgrade can become a lot more complicated because you’d need an entire new wheel with a MICRO SPLINE or XD hub, or a new MICRO SPLINE or XD hub with which you can rebuild the rear wheel. Both of these options can be quite expensive. In rare cases you may be able to upgrade your hub with a MICRO SPLINE or XD 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 and 11-50T cassettes that fit onto the HG Standard freehub bodies and are specifically designed to be compatible with all Shimano and SRAM (respectively) 12-speed derailleurs and chains. The main difference is that the smallest cog on the SunRace cassettes is 11T vs. 10T on the Shimano and SRAM cassettes. We’ve put together a multitude of upgrade kits which include these HG SunRace 12-speed cassettes for Shimano and SRAM drivetrains ranging from Shimano Deore 12s M6100 and XT M8100 to SRAM GX. 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 or even 8-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 cassettes will fit and be a great upgrade option.