When Shimano released its new 12-speed GRX group, it managed to add the extra gear by using existing standards. Sort of. If you’re looking to bring 1x GRX to a gravel hub, you’ll still need a microspline conversion kit.

While GRX 2x groups borrow Shimano’s HGL2 standard from 12-speed road, the 1x version uses Shimano’s Microspline cassette body. Microspline is well established in mountain biking (GRX actually just uses Shimano’s mtb cassettes), but mountain biking uses a different hub spacing than most gravel bikes.

While Shimano had its own wheelset ready for lauch, boutique hub brands were left trying to catch up. Those are now starting to land on the market. Chris King and Easton both now offer conversion kits to make Microspline work with road spacing hubs.

Chris King R45D conversion kit

Portland boutique hub brand Chris King has always presented its hubs as “forever” hubs, backing the made-in-house bearings and hubs with a lifetime warranty. To keep forever feeling fresh, King is offering a full conversion kit for its R45D hubs.

The conversion kit includes the axle, freehub body and all driveshell internals. Kits are compatible with with all centerlock R45D hubs and with Gen. 2 six-bolt hubs (serial numbers starting 691XXXXX). That expands R45D compatibility to include Shimao HG, SRAM XDR and now Microspline.

King offers the kits with steel or ceramic bearings and in black or silver. R45D conversion kits are available as of January 1 directly from Chris King and from retailers. They start at $250 for steel bearings kits or $310 for the ceramic bearing option.

Easton Vault hub conversions

Easton is also getting into the Microspline game with its Vault hubs. With partner brand Race Face well versed in Shimano’s 12-speed standard, it’s not surprising Easton was quick out of the gates. In fact, we already have one racking up miles on an AX wheelset. It also helps that the Vault hubs allow for easy, tool-free cassette body switches.

Since it’s just the cassette body and end caps that need changing, Easton offers the Microspline option for $75 as a quick upgrade to the Vault hub (including end caps). Kits are already available for AX90 (EC or EA) wheelsets that use the Vault hubs. Fun Fact: since Race Face uses the same Vault hub and endcaps for hub spacing, Microspline cassette bodies are cross compatible between Easton Vault and Race Face Vault hubs.

Easton is also offering Microspline for AX70 wheels (X5CL hubs), though stock may not yet have arrived online.

With GRX’s move to 12-speed, Easton also now offers chainrings for the Shimano HG+ chains used on 12-speed drivetrains, from 38 to 44t in two-tooth jumps.