Crank Lengths on XC Mountain Bike

I’m just about to pull the trigger on a new Full Suspension XC MTB. All my road bikes have 165mm cranks on them as a result of a very good bike fit. As I’m 5’ 11" the MTB’s I’m looking at come with 175mm cranks. Would it be worthwhile changing to shorter cranks after I’ve got it? My initial thought is probably not as a) I won’t be as low on an MTB so opening my hip angle isn’t going to be relevant and b). I think that most of my MTB’ing is less spinning and more grinding so a longer crank should help. Finally longer cranks would have me sitting lower so my Centre of Gravity would be lower which I would think would be a good thing.
Anybody got any thoughts on the matter? Thanks

The biggest reason to go shorter for MTB cranks is for ground clearance. With the push to lower BB height for handling, coupled with full suspension compression, you can get a lot more pedal strikes. So, many people have swapped to shorter cranks (and some manufacturers are following suit these days too) to get more pedal clearance.

It’s different animal than just about any road cycling, with the notable exception of crit racers or others looking to increase pedal clearance for corner pedaling.

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Agree with Chad. Rocks cause a lot of pedal strikes riding XC, so having shorter cranks is a nice benefit.

I’m 5’9” with shortish legs and use 172.5mm on the road and 170mm on MTB. Pedal strikes is the main factor, but there also generally seem to be less options on MTB cranks. You’re not often sitting and spinning for long periods of time on the MTB either so optimizing for pedal efficiency becomes less important.

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I’m 6’1" on a Scott Spark with a low BB and 175mm cranks. Sure I had pedal strikes when I first got the bike but after a few months it was all but gone. You just get used to where can and can’t pedal.


Thanks for the replies chaps. I ordered the bike and got them to change the cranks from 175 to 170’s

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Yes, 100% agree. 5mm of extra clearance doesn’t seem to offer much of a difference. Timing your pedaling on technical terrain is a skill all mountain bikers should have. That said there’s no reason to not got to 170 but if the bike comes with 175 I wouldn’t switch unless you’re really banging pedals

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FWIW I’m 6’0, so close to the same height.

I’m running 165mm on road, XC, and DH bikes.

My enduro bike (SC Nomad) came with 170mm and is the oldest in the fleet. I switched to 165mm on other bikes after I had bought the Nomad. No complaints with the 170mm, as the difference is not noticeable, especially considering the dropper has a bit of squish in it.

If you were building up an XC hardtail with rigid post, I’d be inclined to say that the crank length would be a bit more important.

I prefer the feel of longer 175 cranks for “hammering” versus “spinning” but that’s personal preference. You get used to “ratcheting” your cranks to avoid strikes very fast.

I have 170 cranks on my trail MTB, and HAD 175 on my XC bike. I just put a ROTOR power meter on my XC bike, and decided to try 165 (wanted to go extreme to see if I could tell a difference).

I like the 165s on my XC bike. I feel like it is easier to spin faster. I was struggling with maintaining a cadence around 90, but now it does seem easier (I was at about 80, on average). I haven’t felt like my ratcheting or power move stomps have suffered at all. No knee pain or anything, for what that’s worth.