Shorter Cranks

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WorkonSunday
Posts: 540
Joined: Tue Jan 16, 2018 4:39 pm

by WorkonSunday

im 171cm, i used to use 170mm crank that came with the bike, then by chance i picked up a 172.5mm. i notice it was noticeably easier to accelerate when out of saddle. i was so very curious about the difference, i start experimenting with different lengths. Fast forward a few year, i later found out that was because acceleration is about the torque more than power. power is required to sustain the speed once you get there.

i also looked at the impact on the bike fit, with longer crank, the hip moves alot more and just feel quite unstable at higher cadence. as i moved down to 165 and 155mm, the hip becomes more stable and it was easier to sustain higher power. However, for me, 155m has too little torque, even slight change in gradient or wind speed, i had to constantly change gear. Think of it as a diesel truck, the torque band is very narrow and you need to constantly changing gear to ensure you stay within the effective band. low cadence really tires the legs and prone to cramps in calf and quads. I now settled for 165mm for road bike and gravel bike. for Tri bike, i use 160mm. going mtb, i use 170mm as high cadence isnt as important as those sudden peaks that need high torque/anaerobic power to get past.
Last edited by WorkonSunday on Wed Nov 24, 2021 1:08 pm, edited 1 time in total.
Some say pour 10ml water out of your bottle to save that last bit of the weight. Sorry, i go one step further, i tend to the rider off my bikes. :thumbup:
n+1...14 last time i checked, but i lost count :mrgreen:

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wltz
Posts: 335
Joined: Tue Jan 14, 2020 10:49 pm

by wltz

fsp15923 wrote:
wltz wrote:
fsp15923 wrote:
Wed Nov 24, 2021 6:21 am
Hi, I am same height wity 172.5 crank, looking to move to 170 but I would like to know if there was a noticeable difference in power output?

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Power output as in peak 1s power or average numbers? Conventionally you give away some of your top power by going shorter cranks. If my PM numbers are to be believed, I could hit 1200W max on 170mm cranks for 1 second, with 165mm cranks that's down to 990W. But my 5s, 10s and 15s power numbers are all higher now. I'm not a sprinter nor a crit racer, my game is long distance, and in it shorter cranks make a difference. FWIW I can still start off the lights on 50-11 on a good day, if I am feeling playful.
Thanks, so by inference, the average power increased over longer distance cycling...for me that is anything over 100km. Short of not knowing your setup, its hard to compare wiith what I intend doing. I guess I will have to venture and find out for myself.

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Unfortunately, my work/life balance took a tilt in the wrong direction just as I went down to 165, so my form experienced a soft landing making me a poor lab mice for direct comparisons. However, I compared two smashfests ridden over similar terrain in autumn 2020 - at peak form, and in March 2021 - early season form with some hours on turbo (power numbers from Strava):

170mm cranks (2020): 214W average / 248W weighted average at 83 average Rpm
165mm cranks (2021): 224W average / 244W weighted average at 91 average Rpm

So speculatively, I could sustain similar power output being in an inferior form, at higher average cadence, but I am not confident enough to draw any serious conclusions.


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Juanmoretime
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Posts: 289
Joined: Sat Jun 19, 2004 11:08 am

by Juanmoretime

I'm 186 cm tall. Rode 175mm cranks years ago and felt better going to 172.5mm. I still ride 172.5 on both raod bikes and my gravel bike. I did try going back to 175mm and I realize we are talking about 5mm differnce in pedaling cirlce but I could feel the differnece. Just llike in the past I felt a few millimeters differnece wth post slippage. I do ride 170mmon my fat bike.The only differnce going from 175mm on the fat to 170mm I spin a lot more.

What made the biggest differnce to me was going to eTap. I used to be a gear masher and now spin much more since that now higher cadence seems to be the sweet spot. My average ride avergae speed went up slightly too. It wasnt gaining fitness since my training volume has actually gone down down to my work load at my job. That is soon to end!

Andrew69
Posts: 593
Joined: Thu Feb 19, 2009 10:52 am
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by Andrew69

fsp15923 wrote:
Wed Nov 24, 2021 10:53 am
Andrew69 wrote:
fsp15923 wrote:
Wed Nov 24, 2021 6:21 am
wltz wrote:I'm 178cm / 5'10" and I've gone progressively down 172.5-170-167.5-165. I've never looked back. My average cadence has stayed the same more or less (when cruising / tempoing I revert to my natural range), but I can maintain a higher cadence at threshold, which is what matters. What has changed is I'm not getting any knee pain from overuse. Dialling in the saddle position can take some time, but is worth it in my book. I would say you can feel 5mm of difference, I still have 172.5 cranks on my "turbo" bike just because I'm lazy, and the difference is noticeable.
Hi, I am same height wity 172.5 crank, looking to move to 170 but I would like to know if there was a noticeable difference in power output?

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Torque, yes
Power, no (as explained above, a natural increase in cadence will make up for the lower torque output)
Thanks but what is your blade sizes? Mine is 52:39. With the imminent move to 172mm crank, I was thinking of a change from 39 to 36 as well. Any difference in torque versus power in this instance? Cadence will increase and climbing should improve though. Any thoughts from those who ventures this route?

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I run SRAM Red AXS on my bike with 165mm cranks (came with 172.5) and there is a definite differnce in how I now climb vs "traditional" gearing and crank length
No more mashing of the pedals, now its spin, spin , spin. Much nicer for the knees

daninplymouth
Posts: 129
Joined: Mon Sep 20, 2021 1:50 pm

by daninplymouth

Thanks for the feedback. Definitely something I'm keen to explore may have a look on eBay and see if I can find a used crank to see how it feels before splurging on a new one.
Trying to save my monies for a new set of wheels at the mo

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