Due to an old injury I’d really like to move the LH crank in as far as possible; there’s unfortunately virtually no wiggle room on the RHS. The bike currently has RaceFace Aeffect cranks, and I don’t think there’s a shorter spindle available. The cranks are 175mm too, and I’d prefer 172.5 (ideally), or else 170.
Is there anything that might work, preferably not super rare or hyper expensive? Compatible BB recommendations would help too.
Your best option is probably to pick up a set of XTR XC cranks, unless anyone has any particularly bright ideas. they’re fairly low q-factor. The shell width doesn’t really matter – BB92 is the same external width as a 73mm shell with a BB screwed into it. Also, 24mm Shimano axles tend to get better bearing life than 30 or 28.9mm in a 41mm aperture frame like BB92
You could also try narrower Q factor pedals if they would work with your pedal stance. Most SPD’s have a Q factor of 55mm.
Shimano makes a 52mm Q factor XTR pedal, or the new Wolftooth pedals which are adjustable can be set to 51mm.
Moving this to Tech > Tech Help, due to it’s technical nature, from a bike fit standpoint.
Unfortunately, the bike has flat pedals, so saving a few mm via shorter pedal spindles isn’t going to work.
At present the Q factor is 175mm, assuming the default 137mm spindle is present. There’s apparently one ~2mm shorter but that’s not worth worrying about. There’s ~5mm clearance between the inside of the RH crankarm and the elevated chainstay on that side, so that arm can’t realistically come in more than 2-3mm at the most; on the LHS there’s ~10mm of room.
It might be worth trying to use some sort of Shimano MTB crank on the RHS (if I can find something that gives suitable clearance) with a non-matching road, GRX, or XTR 985/9000/9100 LH crank. I’ll see what I can find…
Many of the current XTR cranks don’t use the two-bolt pinch system, it is more like the old Octalink attachment. I have a set of XTR cranks, can’t remember exactly which ones (the ones with the 2nd lowest Q-factor I could find for 12speed), LMK if you want any measurements. The cranks barely clear the chain stays on my 29x2.4” tired full suspension bike, Q-factor is ~167 IIRC.