A Guide to Shimano’s 12-Speed Freehubs and Compatibility

New innovations in Shimano freehub technology have delivered even more robust and reliable shift systems along with wider gear ranges for 12-speed road, mountain bike, and gravel groupsets. Each freehub system offers unique features and compatibility options that are suited for different riding styles and rider needs.

Here is a quick guide on Shimano 12-speed MICRO SPLINE, HG L2, and HG freehub systems and what to consider when selecting the option that’s compatible with your cassette and drivetrain.

The HG L2 freehub is the cutting edge of premium road technology and was launched with the latest generation 12-speed DURA-ACE 9200 groupset. It was specifically engineered to allow new DURA-ACE 12-speed cassettes to be made from aluminum instead of titanium, while still maintaining positive engagement between cassette and freehub.

Aluminum is lighter and more cost efficient than titanium when it comes to freehubs, but it’s also easier to damage. Before the HG L2 design, aluminum freehubs would quickly show signs of pitting due to the high pressure and small surface area where the cog contacts the freehub. The HG L2 design eliminates this issue by using smaller, deeper splines on both the freehub body and cassette cogs, which disperses these forces while capturing the benefits of aluminum.

The HG L2 freehub is only compatible with Dura-Ace 12-speed road cassettes that can be used with 12-speed road and gravel groups. However, Dura Ace 12-speed cassettes are backwards compatible with HG freehubs, which accept both 11 and 12 speed cassettes.

MICRO SPLINE freehub technology was first introduced with 12-speed XTR mountain bike drivetrains in 2018 and has been utilized throughout Shimano’s premium mountain bike range since. Now, MICRO SPLINE has trickled into gravel with Shimano’s 1x12-speed GRX gravel groupsets.

MICRO SPLINE accommodates the wider gear ranges of 1x12-speed setups including a 10-51-tooth cassette. With this setup, the small 10-tooth cog delivers top speeds for the fastest MTB and gravel races while the 51-tooth cog keeps riders spinning longer on steep ascents.

Shimano GRX 1x12-speed groups are designed to be used with MTB cassettes, creating a seamless pairing with MICRO SPLINE freehubs. The specific orientation of the splines aligns the shift ramps on each cog allowing HYPERGLIDE+ technologies to provide secure, uninterrupted shifts up and down the cassettes.

The HG freehub design works with the widest range of cassettes across Shimano’s road and gravel groupsets. It’s been in use for over a decade and is compatible with Shimano 12- and 11-speed road and 11-speed mountain bike cassettes (see note below about spacers).

The HG freehub design feature specifically matched splines that orient with the cassette cogs for a seamless engagement. It’s this orientation that also aligns the cassettes shift ramps between cogs, delivering Shimano’s HYPERGLIDE+ crips and secure shifting up and down the cassette.

**The HG-800 and HG-700 road cassettes and 11-speed mountain bike cassettes are compatible with HG freehubs, but require a 1.85 mm spacer.