Hi
Was looking at buying an slx double and bash for a BFe build. But how do you know what length? 170/175mm? I am 5′ 11″ if that helps and frame is medium.

Anybody! 😆

175. Almost everyone uses 175, only change if you’re extremely tall/short (which you’re not!). I’m the same height and on 175mm – on a BFe too!

Some people do use shorter cranks for better ground clearance, but 5mm is of dubious benefit and your pedals should be level in tech terrain anyway!

I have an SLX double and bash too and went for 175mm cranks. Its what length the Alivio set-up was on my previous bike so I just stuck to what I was familiar with. I’m 5′ 9″ and my frames have been medium too, hope that helped a bit?!

I’ve got some 170mm length ones for sale in the classifieds if you are interested.

Always thought bigger was better and more powerful etc but after much pedal whacking on my Pitch I plumped for 170mm SLX double and bash. Not really noticed any difference other than less pedal strikes.

Oh and I’m 6’1″

at 5’11” almost def 170. – what Stevo said doesn’t really make any sense, in actual fact you should only really need to go to 175 if you’re extremely tall (which you’re not) 😉
he also said almost everyone uses 175, and that’s true! but only because that’s what’s spec’d OEM 99% of the time and that’s also what’s more often available/cheaper/discounted online too.

5’11″(and a half)
tried 170,175s feel much better.torque and all that.
on the road I’ve tried 165,170 and 172.5,170 seems right.

so,if your cadence is high,like it would be on the road,90+
get 170s.if it’s a bit slower,175s help.and give you a bit of a wider stance when you’re standing up.

but crank length is a bit like saddle choice.
so,buy both,and make your own mind up.
dh folks often run shorter cranks,but they’re not really pedalling up.
ss often run longer.

are your legs short or long for your height?
height of saddle to centre of bb is 73cm aprox for me,depends on the pedals.

Moutainbikings in the torquey end of cycling. 175mm will be fine unless you spin along at 90 plus.

Thank you for all the input everybody much appreciated.

I can’t really see any advantage of a longer cranks if you’re running gears. Longer crank just equals less ground clearance.

It will make 3.4372% difference to the way your bike rides. It’s only 5mm. What happens when you get 5mm worth of mud on your tyre, or you ride over a tiny pebble, or your tyre compress or your suspension moves?