Looking at experimenting with some short cranks to try and reduce ground strikes, which I know could be avoided if I was less crap but that’s harder to overcome compared to some new cranks!
I’ve read a few articles about the advantages, found some m8000 cranks on the bay which are identical to my current only 165 instead of 175. I know folks here have spent time fine tuning their bikes and wondering what folks feelings are on short MTB cranks.
Probably worth saying my stats, I’m a pretty small dude at 170cm, normally ride medium or small bikes and around 64 - 65 kilo after I deal with Xmas weight!
I’ve ridden 175, 172.5, 170, 165 & never noticed any real difference if I’m riding in a regular road position. But I’m a macro absorber not a micro adjuster when it comes to bike fit. So if you want to put on 165mm crank arms you should do it with a clear conscience. However, if you really notice mm sized changes to your seat post or stem it might be a different story for you.
One are where shorter cranks arms did make a noticeable difference for me, though, was on my TT bike. For what was my dialed, tested stack height the shorter cranks definitely gave me more ‘room to breath’. It was definitely much more pronounced than I thought it would be.
Well I’m a 5’2" (158 cm) road/gravel/cyclocross rider and have always ridden 165 mm cranks. I’m a high cadence style rider and need a larger hip angle (something with my left hip) so it fits my style and needs. YMMV. I can’t say whether you’d actually notice the difference.
I’m 6’3”, 225lbs.
Usually I run 175mm cranks (which are probably correct ply sized based on the length of my femur) but my 2021 Rocky Mountain Instinct came with 170mm cranks. I did not notice for the first month until riding my hardtail with 175mm cranks back to back days.
After a full season on 170mm I can say the following!
My overall cadence is +10 higher. This makes it easier to generate power using leg speed.
My peak power (standing climbing, sprinting) is slightly lower for any given cadence. I have adapted with faster legs. I could also have swapped from 32t to 30t or 28t to get more torque form higher power output.
They don’t really prevent crank strikes, but the Strikes are a little less severe. Due to the low BB height of my new bike, I have had to adjust my suspension (more volume spacers for mid stroke support) and my techniques (better trail scanning to facilitate better timing to avoid strikes) to handle crank impacts, although I don’t really have a lot of crank impacts in general.
So, I’d say go for it, assuming you have a decent pedaling cadence overall. Should hold you back at all.
I’ve ridden 145’s and 155’s for a bit on my road bike. One thing that caught me off guard that I imagine transfers to MTB is that as I raised the saddle to maintain knee angle at BDC my center of gravity got pretty high which took some getting used to.
I switched from 172.5 mm cranks to 165 mm cranks on my road bike in order to alleviate fit issues. I have long limbs and with the longer cranks I tended to massage my stomach with my knees when I was in an aero position. The shorter cranks really made a difference. Shorter cranks also help with pedal strikes, that’s for sure.
Otherwise, they just give you another degree of freedom to dial in your fit. But even in the “worst” case there is no appreciable difference between longer and shorter cranks if you can make the bike fit your body. If I were to build a bike from scratch, for sure I would opt for shorter cranks.
I went from 175mm to 170mm cranks and it’s made a big difference in my bike fit.
I dropped 10mm up front off my stack, had to raise my seat about 8mm and moved my seat slightly rearward. It’s allowed me to roll my pelvis further forward and be comfortable in the drops w/o hitting my gut w/my knees. The result is being more aero and I can pick up almost a MPH vs. my old position at similar watts. I can corner more aggressively as well, but it’s not been the primary benefit.
My avg. cadence went up about 6-7 RPM. I don’t see big changes in power, but I’m still a relatively new rider on an upward slope for FTP gains.
You’ll probably need to move your seat back a little to keep the pedal spindle in appropriate alignment vs your knee. And may need to shorten the stem as a result.
This will put your weight further back on the bike (about 1 cm if you match the crank difference) which may mean you’ll have to work more to keep the front wheel down on climbs.
But the overall impact is reasonably small (1cm mentioned above).
What kind of bike do you have? Some bikes are more prone to pedal strikes than others. I had a 2017 trek fuel that was prone to pedal strikes. I changed to a 2021 trek fuel frame when I got my frame replaced under warranty, and the 2021 frame is way less prone to pedal strikes.
So the alternative to shorter cranks is to get a new bike
Funnily enough, that’s the genesis of this experiment. I’ve lost a lot of mojo specifically on the mtb, but tbh also in lots of different places, I didn’t like my brakes and how little confidence I had and the strikes I was getting. I’ve had new brakes for a month and now cranks so hoping it feels better. Then will be looking for a 29er if I ride her more and enjoy it again.
I’m 180cm but have very short legs, 76cm inseam. I went to three well-regarded bike fitters and none of them suggested crank length to me, I ended up replacing my 56cm frame with a 54cm frame because all three fitters said my current frame was too large for me. Guess what, I should’ve just gotten shorter cranks.
I’ve been using Rotor’s Aldhu oval chain rings with 155mm cranks for the last 2 years and am very happy with the setup. My personal benefits have been:
More aerodynamic. I can get lower in the drops without my knees hitting my torso.
I can pedal through turns that most folks can’t.
I can spin up noticeably faster than when I was using 172.5mm cranks; granted this is largely due to gearing, but it also disproves the argument that longer cranks provide more leverage on geared drivetrains.
I get to be a shorter crank apologist to the folks that poke fun at me for running “women-sized cranks”.
I love Rotor cranks for their modularity and the fact that they do offer unusual crank lengths and the like. Plus, the quality is top notch.
Ignore the haters.
Plus, women’s bikes (or smaller bikes) don’t get 155 mm cranks either. I think the smallest crank size I have seen by default was 165 mm, which is what I have on my bike now.
Crank length does give an extra dimension to fitters. My fitter (a former world tour pro team mechanic, so no dummy when it comes to bikes) also initially balked at the idea. I asked him to let me try it. So he just took the crank off a random bike in the show room (a woman’s bike, I think ) and let me try it. That settled it for me, 165 mm it was for my next bike.