Moving to shorter crank lengths

[wheelsONfire]

I had to wait a loooong time for a Rotor crank back in the days. I was recommended to go from 172.5 to 175.
Worst decision, it was a kill blow for my knees!
170mm works good accept that i kind of pushed a bit to hard first hours.
Felt as i was moving feets in to big circles. In the end i went with 172.5 but sure, i could give 170 another try, but never again 175.

[rwoofer]

I'm not sure if this makes much difference, but I'm pretty tall, 187cm, so I'm well within the fit window for 175s.

Where did you find the fit window? I'm 198cm so 175mm cranks might even be small for my height!

[rothwem]

I'm not sure if this makes much difference, but I'm pretty tall, 187cm, so I'm well within the fit window for 175s.

Where did you find the fit window? I'm 198cm so 175mm cranks might even be small for my height!

I mean, its all pretty hypothetical, but Zinn Cycles (a maker of super long and super short custom crank arms, so grain of salt is probably required) recommends 21-21.6% of inseam length, so that puts me at ~180mm for a conservative length with my 34 inch inseam. I'm pretty sure the goal is just to make sure that your knee doesn't exceed 90 degrees at the top of the stroke for a seat height that doesn't make your hips rock at the bottom so that leaves a pretty broad range of crank lengths.

[rwoofer]

By that calculation, my cranks should be 200mm. Think I'm safe with 175s!

[DaveS]

I just switched one of my bikes from 175 to 170. I raised the saddle by 3mm and scarcely noticed the difference.

[Spurdo]

The only difference I am feeling switching from 175 to 165 on my TT bike is that it feels easier to rotate hips forward and top of the pedal stroke feels easier. I am not seeing any differences in power but left / right balance has gone absolutely bonkers 44/56 and 43/57 on ~10 minute efforts. Need more km's though, had similiar inbalances on 175 too.

First ride I did was with no other changes and on second I raised seat by 5mm.

[recoilfx]

I'm 5'7 (170cm) with a 30" inseam (76cm), and I always felt kinda of off when riding in the drops trying to produce power. I was already on a 165mm crank, but when I saw that Rotor offered the Aldhu's down to 150mm, I decided to give that a try.

The first ride (an 5.7 mile hill climb race) felt strange at first, but by the end of it, I barely noticed anything other than that my natural cadence went from ~92 to ~98. Riding in the drops aggressively also felt better (though I haven't analyzed whether power improved or not).

I raised my saddle up by about 15mm and I didn't feel the need to raise my bar. I will see how my neck and back are doing after doing longer endurance rides later. I did used Sheldon Brown's gain ratio calculator to figure out what gears I need to change to keep the gain ratio after reducing the crank length. As it turned out, I need to go down from 50/34 to 46/30 on the front, so getting the sub compact chain rings to shift well took quite a while on my bike.

[wltz]

I now have 165 or 167.5 cranks on all my bikes and will never go back to 172.5. I'm 178 cm with 82.5 inseam. Whilst I did observe some marginal increase in seated climbing cadence when I first went short, I failed to notice any "loss of punch" some riders reported here: I can still get going from a standing start on 50-11 without much trouble or stay in the big ring on 10% gradients (and that I can do because I squat 100kg for 10 reps and never miss a legs day). Also my cruising cadence has not changed, it naturally averages 78 whatever crank length I use, I am just able to produce decent power in a more aero position. My takeaway from my experiments is that 172.5 is too long a crank for most people of average height (for a Caucasian male).

[spartacus]

I have bikes with 170, 172.5, and 175 and I can't really tell a difference while I'm riding them.

I would be really curious if people could tell in a blind test.

[MarshMellow]

I have bikes with 170, 172.5, and 175 and I can't really tell a difference while I'm riding them.

I would be really curious if people could tell in a blind test.

There's a difference between my two most similar frames, one having had 172.5mm for All Road, Gravel, Hill Climb and the other solely Road and 175mm. Upgraded to 175mm and there's no way that a change is not being had when able to call upon the longer lever of the crankarm and, the increased swept-area being leveraged into, over and through.

Cadence is a non-issue for the most part, since the Gravel Bike is being in constant state of adjustment. The Road Bike I've dialed in and enjoy the reserve had from 175mm/53-39 11x28 If every throwing a leg over a true TT bike then, of course applying effort with such gearing and shorter cranks will easier achieve an advantage but - is all personal preference so long as a rider is able to pedal smoothly

[maxim809]

I went on a road cycling tour many years ago with a bunch of random people... It's one of those things where the tour company prepares rental bikes for you, and off you go.

Me and one other, normally used to running 170mm's, were constantly adjusting our saddle height during the first portion of the trip. Just trying not to make a scene, and to be polite.

After a 2 hour long climb, feeling uncomfortable but manageable, we finally thought to look at the crank length. Turns out all the rental bikes had 172.5mm's regardless of frame size.

So we couldn't really pin-point WHY the bike felt weird, and back then I wasn't the type to really think about anything as much as I do now. So despite being totally ignorant, at least us two in the group definitely noticed the different between 170mm vs 172.5mm...

Mind you we were both short, so I think from our perspectives running even slightly longer cranks is far more noticeable than an average person running the spectrum of average sized cranks.

So ya to drive that point even further-- that's not even a blind test. It's a DOUBLE blind test. Because the people fitting our bikes during the initial setup didn't even think to tell us about crank lengths. We gave them our nominal saddle measurements, did the fine-tuning adjustments during the pre-ride, had everyone look at each of us to spot-check our saddle heights, got the thumbs up, and off we went.

Pretty noticeable for me, because you end up sitting differently on the saddle too. But I can believe some people won't notice the difference between even +5mm of crank length difference.

We all different I guess.

[warthog101]

184cm tall.
Raced tts on 177.5
Faster for me.
Ride 175 on my roadie.
Tried 172.5 and climbed marginally slower.
Perhaps I could try them again or go smaller but cbfed.
175 is comfortable and works for me.

[Nohands83]

184cm tall.
Raced tts on 177.5
Faster for me.
Ride 175 on my roadie.
Tried 172.5 and climbed marginally slower.
Perhaps I could try them again or go smaller but cbfed.
175 is comfortable and works for me.

I'm the same height, and use 170mm across on road and gravel, 165mm on TT.
It's very individual.
The only way to really find out what works for you is by testing - riding hard for sustained efforts.
I got a lot of practice and data when racing TTs so it was very easy to tell shorter is fast for me.

[ODC]

I'm 193cm tall and my saddle height (center bb to top saddle) is 81,5cm. I raced years with 175mm cranks and even tried 177,5mm cranks but the last 5 years I changed to 172,5.
The 175 mm cranks where the sweet spot when I raced. When I tried the 177,5 (yeah it's only 2,5mm longer) I felt immediately that i could push a bigger gear/had more torque but I lost my higher cadence. So switched back to 175mm.
Now that I'm done racing I went to 172,5mm and I fell more comfortable with them. It's the feeling that I can spin more and be more relaxed on the bike there I'm not racing anymore. Also to sell a bike or crank it's more easy with 172,5mm cranks.

[blaugrana]

I'm 192cm tall and have almost always used 175mm cranks. I think that the observation that proportionaly it is a "short" crank for my height compared to what 170 or 172,5mm are to most people is quite interesting, because despite not being very flexible I never struggled with aggressive positions on the road bike, even on long endurance rides. I never looked at it from this angle, but it would make sense that the "short" cranks help with the aero position, just like people running very short cranks on TT bikes have been doing for quite a while.

I have also tried 172,5mm on an old cyclocross bike bought second hand, and while I could feel the difference, it was too small to tell if it was better or worse (which is consistent with some studies showing almost no differences in power when varying crank length as long as somewhat reasonable biomechanics could still be achieved).