MTB: 170 vs 175 cranks

[benyl]

I'm building up a Tallboy and am wondering if you guys think there is a difference. Internet is mixed.

I've ordered 170mm, but I might bump up to 175mm.

Current Nomad has 27.5" wheels, Eagle drivetrain (10-50) and 170mm cranks and 30T chainring. No issues with knee pain or anything. Going up steep stuff is a geometry limitation rather than a "power" limitation.

Going XT on the Tallboy (10-51) with a 30T chainring. With 29" wheels and the 51 in the rear, the gearing is the same with 175mm cranks.

170mm cranks should make pedaling 6% harder than what I am used to now. Is that even perceptable?

170 or 175 or it doesn't fucking matter, just ride.

[Penguin_Racecar]

Personally I'd go with 170mm because you know it works for your knees. You can set your saddle height to the exact same as the Nomad and be on your way. No cleat adjustment needed either if you're on clipless. Like you said, it's not a power limitation so going up to 29er wheel probably won't be an issue for you.

[dimi]

Moreso dependent on your inseam than anything, and a 5mm change will be barely noticeable. I would suggest a 32 or 34 chainring. 30x51 is way too low of a ratio, especially for a xc duty bike.

[revelations]

haha, I had a 170 and 175mm cranks for a while and never noticed it - now with my 29" bike I have 180s.

[bigboom]

The other consider here is clearance. Are you hitting your cranks on the ground right now with your Nomad? The TB sits another 10mm lower in bb height compared to the nomad so if you went to 175 you might have issues as you would losing 1.5cm in clearance, id stick with 170mm.

[benyl]

Update: Went with 175mm

Don’t notice a difference pedalling at all.
Descending, though, I can definitely tell that my feet are further apart.