crank length

Beyond the whole controversy about a smaller "dead spot" it's true your knee won't be as bent at the top of the stroke but don't a longer lever need less force?

When you got no momentum and your back wheel has dropped between two roots which length lever gonna' be easier to muscle you through?

If you focus on downhill, this is a non-issue.

165 FTW.

having recently gone from 170 to 175 (at 6'1'', so not quite as tall as you, OP). I must say I really do prefer the 170s, they are on the same bike. I just feel more awkward pedalling the longer arms.

this may be due to running 170s forever, but still, I won't be staying at 175.

Posted by: tungsten

Beyond the whole controversy about a smaller "dead spot" it's true your knee won't be as bent at the top of the stroke but don't a longer lever need less force?

When you got no momentum and your back wheel has dropped between two roots which length lever gonna' be easier to muscle you through?

The leverage argument is somewhat nulled by gearing, unless you are making the comparison at the lowest or highest gear you 'should' end up in a different gear to counter a loss in leverage.

I'm making the comparison for whatever lowest gear in any given drivetrain @ grunt speed..

DH bike - 165

Mojo G16 - 165

Surface - 175 (should’ve went 170)

Road bike - 175

26” 6” bike - 175

Posted by: JBV

Zeus, why did you go to 175's?  at first i scoffed at the idea of 5mm making any difference, but apparently it does, and mitigates pedal strikes.

honestly they were on sale and I wanted to try something with more leverage.

I'm 6'6" and tried 180s for a while. I liked the way they rode but the clearance issues were enough that I switched back to 175. 170 just felt too small. 175 is a good compromise for me.

I have a 31 inseam, 5’5” and I like 175. I used to always run 170 until I forgot to specify that on a group a long time ago but I preferred the longer crank. I don’t hit my pedals hard very often so I suppose I have learned to adapt.

lots of scientific or pseudo scientific studies have shown no real difference in sustained power between 170 mm and 175 mm (other stuff happens at weird crank lengths on stationary trainers, but I don't think that is relevant to mtn biking)
one New Zealand study with the national XC team showed that with the shorter crank the riders could get to their maximum power faster, but after that, no difference

One poster already mentioned the ability to get out of hole easier with more leverage of the longer crank; however, I could argue that to get in three quick pedal strokes with shorter cranks to get more momentum for a step up on a technical climb would be better

my 29er has 170s, and my 26er and commuter have 175s (until last year I was on 175s over 30 years). I actually like the 170s better

I am 5'11" but have 31" inseam. I went from 175mm to 165mm with a oval chain Ring and it's really great ( same size chain Ring just oval). It seems like the oval ring cancels out the reduced leverage. I did it to help with pedal strikes, honesty. It helps.

Short cranks are awesome. I’m 6’3” and I went down to 165 cranks on all my bikes due to hip issues. I found the pain relief I expected, but I was surprised at all the positive side effects I encountered. Ground clearance is the most obvious one. The ability to pedal through sections where my riding buddies have to ratchet leads to me clearing a lot more technical sections. I haven’t noticed any issues related to leverage. 

The bike feels better on the jumps too. There’s something about having your feet closer together that just feels better in the air. 

On the aerobic side, I’ve found that having a less closed-off hip angle allows me to set up my bike more aggressively without cutting off my breathing. Admittedly, this is more of a benefit on my road bike. The few times I’ve ridden with a HRM, I’ve noticed that I’m doing the same pace/time on my regular 40k road loop with a lower heart rate. 

I think everyone should try 165 or shorter cranks for at least a couple weeks.

I'm 6'3.5" and most XL bikes are not big enough for me. We still have a ways to go on reach. I need it longer. Pedal strikes keep me from riding longer cranks but I would not give up 175 mm cranks. I run 185 mm cranks on my monster cross and 180 mm on my other two road bikes. I have 180 mm cranks for touring too. I love the power of the longer leaver and at my height I don't have to worry about closing out my knee angle on the top of the stoke, it's just a non-issue. 

So it comes down to personal preference. I see everyone here has a full range of preference.

Fixed gear I have run 165 mm but prefer 170 mm and I have run 172.5 and 170 mm on the boards. I even have 177.5 mm cranks on one vintage road bike.

Posted by: craw

I'm 6'6" and tried 180s for a while. I liked the way they rode but the clearance issues were enough that I switched back to 175. 170 just felt too small. 175 is a good compromise for me.

Damn! What do you ride at that height? I would think almost all production frames are really too small for you?