Running shorter cranks ?

single-pivot

Likes Dirt
Well I've run 175 long cranks for as long as I can remember on my mnt bike's .
But lately I've been questioning why I do .
So I'm 6ft 2 and thought that would be why .
But not sure if it's the low bottom bracket on bike's but I'm constantly getting pedal strike .
Either going down hill and going up .
After some big bits of flakes coming of my carbon xx1 cranks I upgraded to some nice alloy SRAM cranks .
And took the plunge and went 170 mm . !
So far first ride is promising .
Less pedal strike . more down hill control .
Tis little harder on the ups .
Any one else pondered the same ?
 

Jpez

Is bad
Yes. Exactly the same ponder. BIkes are getting lower and I’ve been thinking of going to 170’s so will be interested to hear others feedback.
As you say it’s a little harder on the ups maybe an oval ring will counter that?
 

Zaf

Gearbox Frother
For me, longer cranks had less to do with ground clearance whilst pedaling and more to do with my feeling of stability on the bike when I'm at 9:00/3:00 with the pedals. I also like having that length to load into corners and drive the shoulder knobs in. It is a tangible difference, and I went through a few crank lengths on my Stumpy before settling on 175mm (very low slung bike).

I have heard that there's an interesting study showing efficiency with pedal stroke on a shorter crank arm, but I'm not sure how much of that transfers onto MTB'ing where we usually have irregular power outputs to get up and over obstacles, and less of a smooth pedaling motion on account of the terrain.

I think it's something you adjust to in either case though.
 

Oddjob

Wheel size expert
I'm 6'3 regularly ride 175mm and tried 170mm cranks once on my commuter and I got the worst cramps in my legs. I literally had to stop and get a cab home. So I'm convinced there a physiological element to crank length.

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pink poodle

Our man in Japan
I switched to 170mm a while ago. It was a good move for clearance on my dh bike. I also tried 165mm and felt like I was pedalling in the granny gear.
 

rowdyflat

chez le médecin
I ride a low BB 26er sometimes on tracks which are narrow and twisty but have had fewer pedal strikes changing from 175 to 170 mm cranks + also went to lower gears .
Its only 5 mm but thats all you need.
 

Tubbsy

Party Pooper
Staff member
You will definitely definitely feel a difference.

I tried 180mm cranks on a SS commuter bike, and it took quite a bit of getting used to. Ultimately I did come to like it on that bike, but then switching to my other bikes on 175s would feel weird for a few minutes.

I have considered 170s for my trail bike which is known for pedal strikes, but ultimately I've decided it's more down to technique issues. I think timing while pedalling is probably the better option for me.

Worth a try with some cheap cranks though, I'd be interested to know what you think.
 

single-pivot

Likes Dirt
Interesting . I forgotten to mention I run flats ( which I think makes a differences )
As I've been riding with my foot slightly more forward .
Started this on the descent and now on the ups as well .
So far I like it a fair bit
Best is when my foot is closest to the ground on a corner aka Sam hill style , I'm not clipping the ground and seem to have better control .
Not sure if this is real or perceived we'll see .
But defiantly sticking to shorter cranks
5mm is surprisingly enough of a change , I'd say if I had gone to 165 it wouldn't have been OK
 

schred

Likes Bikes and Dirt
Def some real and imagined issues between 170 172.5 and 175. You can run your body dimensions through a few calculators and it will suggest optimum crank length as a guide. I'd be just as interested in that, expected cadence, any bike or setup issues (that affect clearance) as much as rock strike itself. What flats btw?
 

single-pivot

Likes Dirt
VP harrier flats . The reduced pedal strike alone had me converted .My local Nth South trail , was getting so annoying I'd have to do all these half pedals on humps and bumps not this time
 

moorey

Boom!
The irony is...I now run all 170mm, but my bikes BB heights vary wildly. I still ’noticed’ more strikes on the 175’s with higher bb than a did on bikes with low bb and 170.
I only ever run flats, various brands, usually pretty thin aside from some sets of vaults.
Never noticed any difference in fatigue or cramps on shorter cranks, personally.
 

Joe_MTB

Likes Dirt
I once read that 170mm and 175mm cranks were the same dimension, just the pedal thread drilled 5mm further inboard. Don’t know if there’s any truth in that
 

Alo661

Likes Bikes and Dirt
Just ordered a 170 crank this evening from my old work. I'm 6ft 1". Last 3 bikes I've swapped the stock 175 that come on large frames with 170. Ride 172.5 on my roadie, used to ride 165 on my track bike when I had one. Rather run shorter cranks on MTBs now just cause of stupidly low BB heights. I run flats on my MTBs, always clipped in road and track. No idea why 150+mm travel bikes get specced with 175 cranks, it's the one thing that companies have really missed a trick on.
Or you can just go full Freiberg and do this: https://www.ridemedia.com.au/interviews/michael-freiberg-i-ran-200mm-long-cranks/
 

ChrisJC

Likes Bikes and Dirt
I built a steel hardtail 27.5 plus which has a BB height of only 300mm. I put 170mm on and can’t tell the dif between these and 175’s on my other bikes.

I’m 184cm but have longish legs (89cm inseam) and size 47 feet! Yep, big feet, big meat!
 

pink poodle

Our man in Japan
I have size 50 feet...

And would still be a bit like a micro light plane in the Grand Canyon I suspect...

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Is that in cm? Or are you just illustrating my friend should keep expectations on a normal trajectory?
 

Oddjob

Wheel size expert
Euro sizing, not sure if that translates into cm. Yes, and to be honest if that's all your looking for in a man then you will have many other problems.

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stirk

Wheel size expert
If I get a pedal strike most of the time it means I'm not paying attention and have cocked up timing the obstacle. Some obstacles require pedalling to get through and strikes are almost inevitable but it's not worth changing the cranks length, just smash that pedal down so you can upgrade it sooner!
 
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