I have an old Merida Big.Nine hardtail from 2014. It currently sports an XTR M9000 crank, which works well, but is 175 mm long. On my road bike I have 165 mm cranks, which I prefer. This means my pedal stroke on my mountain bike is less even. Since I live somewhere really flat and I use this bike on my commutes, I currently use a 38-tooth chainring.
Given the age and the fact that I will replace this bike within the next 3–4 years with a gravel bike (with flatbars), I was thinking of getting a crank that I can use in the future with a gravel bike frame. The idea is to get another wheelset and then re-use most of the components (which are from 2018–2022).
Specifically, I am interested in Rotor’s modular Vegast or Aldhu cranks. Is it possible to use these road/gravel cranks with a MTB axle on my mountain bike? And then when I switch to another frame, I simply replace the axle with something else?
Should I go for the 24 mm steel axle or the lighter 30 mm axle? Thanks!
30mm spindle is problematic with Shimano BB (pf86/92) so given you don’t know what gravel frame you’ll be getting, you are safer sticking with 24 as that will work great with pretty much any bb design.
I currently have an XTR BB, so I wouldn’t have to change the BB. But just to confirm: is it as easy as changing the axle from MTB to Rotor’s gravel axle?
I should have added this: last time I asked a technical question to Rotor, my support ticket was closed without a response. So I thought I’d ask here instead.
My ROTOR ( last R backwards) is excellent. Bought a 165 Aldhu, bought the ROTOR (last R backwards) BB, has worked perfectly for four years and no sign of issues.
I tried again, and this time they replied within a few hours: apparently it’ll work (yay), but they don’t recommend it as the Aldhu cranks are not made for MTBing. Since this will be a commuter/gravel bike, that won’t be an issue.
I owned an oval XTR M9000 chain ring from them, and the quality was excellent. They even included four exquisitely machined pieces to screw the chain ring bolts into. (The Shimano ones are subtly asymmetric and can turn “out of alignment” while screwing them in.) Peak Torque also raved about the machining of their cranks.
I also like that they are drive train manufacturer-agnostic.
The Kapic (MTB) crank is only available in a 30mm version and Rotor’s MTB length spindles are only available in a 30mm diameter. Ergo, you would need the 30mm version of the Aldhu or Vegast cranks if you really need to use an MTB length spindles. That said, there’s a chance the gravel spindle might give you the clearance you need to run a 38T chainring on a 2014 MTB, which would open the 24mm spindle option back up.
I’m currently running a 38-tooth chain ring with room to spare. I’d be open to running a 30 mm axle for weight reasons. Although I’ll have to replace my Shimano XTR BB, which is excellent.
