While 29in wheels don’t appear to be taking over the entire universe, as promised by some of their more vocal supporters, they’re looking like being here to stay. Certainly Shimano feels it’s worth its while to make 29er-specific parts, although its latest offering is more of an example of the law of unintended consequences.
Aside from the obvious bits – frame, fork, rims, tyres – most parts on 29ers are the same as on regular bikes. But Shimano is now offering 29-er specific hubs. Sounds faintly mad, but there’s a very good reason. Bigger wheels make all your gears feel higher, so if you want the same actual gear range you need to run lower gears. So Shimano is now producing 12-36 9spd cassettes.
So far, so obvious. But then along comes an ISO test requirement that involves putting the transmission in the lowest gear and applying a 1,500N force to the end of the crank (roughly equivalent to a 24 stone person putting all their weight on one pedal). The extra torque generated by a 36t sprocket is enough to make that a big ask for a regular freehub, hence the new high-torque rated M629 (CenterLock) and M529 (six bolt) hubs.
The hubs have a new micro-ratchet freehub body with, it says here, an engagement angle (the maximum rotation before the mechanism engages) of 11.25°. The rest of it is business as normal, and there are front hubs too – presumably just for the sake of consistency.
The 12-36 cassettes are compatible with all Shadow rear derailleurs, which now includes XTR, Saint, XT, SLX and Deore.