Negative effects of shorter cranks

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biwa
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by biwa

Thinking to try out 165mm or 167.5mm crankset, have used 170mm and 172.5mm so far. 2.5mm shorter may not be very noticeable, but I wonder if being >=5mm shorter will produce any side/negative effect on pedaling and power?

I don't race crit so this is not about avoiding pedal strikes, but I do notice with longer cranks my IT bands tighten more after hard rides/intervals, hence the thought of going shorter. I like climbing if that matters.

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AJS914
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by AJS914

That Triathlon Show just had a podcast on fitting where the fitter talks about crank length:

https://scientifictriathlon.com/tts232/

Show notes:

Firstly, what one must understand is that crank length does not affect the ability to produce power, unless we are talking about ridiculous extremes.

What happens when crank length is reduced is that the hip angle is getting more opened up and the knee doesn’t ”bump” into the stomach as much, which makes it easier to breath and also makes it more accessible to getting even lower and more aerodynamic.

So, for me going with shorter cranks is a benefit in almost all situations, and could as well help for those with knee injuries.

Pierre86
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by Pierre86

Main con is percieved lack of torque when climbing or during hard efforts.
Otherwise there's not that much in it and you'll get used to any changes reasonably quickly.
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zefs
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by zefs

It has a negative effect if you are a sprinter and want to do out of the saddle sprints in my opinion but shouldn't be that much of an issue in general. The benefit on climbing is there for the mentioned reasons.

AJS914
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by AJS914

If you go from 170 to 165, you'll probably want an easier gear in the rear to end up with the same gear ratio.

I went from 175 to 170. I really liked the decreased hip angle.

sychen
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by sychen

Biwa.. What's your height and inseam for reference? Normally there is an element of height/inseam vs crank length.

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TobinHatesYou
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by TobinHatesYou

zefs wrote:
Tue May 05, 2020 6:20 am
It has a negative effect if you are a sprinter and want to do out of the saddle sprints in my opinion but shouldn't be that much of an issue in general. The benefit on climbing is there for the mentioned reasons.
This is a bit backward. Track sprinters use short cranks for quick bursts of acceleration and high cadence and at extremely high momentum.

Climbers on really steep grades benefit from longer cranks. As the pedal stroke elongates, weaker muscles in the legs see increased utilization. Even minor increases in leverage help reduce fatigue on those muscles.

alcatraz
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by alcatraz

Shorter cranks can't be more efficient during acceleration. Track riders don't have gears. Can it be related?

I'd summarize short cranks as efficient for sustained efforts and for people with injuries. But I'm not a doctor...

biwa
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by biwa

Pierre86 wrote:
Tue May 05, 2020 6:06 am
Main con is percieved lack of torque when climbing or during hard efforts.
Otherwise there's not that much in it and you'll get used to any changes reasonably quickly.
So it's preceived reduction in torque, not an actual reduction? I think I've read somewhere with shorter cranks you need to increase cadence to maintain the same power?

biwa
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by biwa

AJS914 wrote:
Tue May 05, 2020 6:27 am
If you go from 170 to 165, you'll probably want an easier gear in the rear to end up with the same gear ratio.
Interesting, how does that work? Why crank length affects gear ratio? I thought gear ratio is completely dictated by chainrings and cassette sizes?

Pierre86
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by Pierre86

alcatraz wrote:
Tue May 05, 2020 6:47 am
Shorter cranks can't be more efficient during acceleration. Track riders don't have gears. Can it be related?

I'd summarize short cranks as efficient for sustained efforts and for people with injuries. But I'm not a doctor...
Track sprint is as far removed from road as you can get, other than it being on a bike there is very little carry over between the two. Short cranks are better for track sprinting but for various other reasons
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biwa
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by biwa

sychen wrote:
Tue May 05, 2020 6:32 am
Biwa.. What's your height and inseam for reference? Normally there is an element of height/inseam vs crank length.
178cm and 80cm. I always thought height/inseam doesn't matter too much here unless you go very long/short, because you can always adjust seat height and fore/after to accommodate the crank length.

Pierre86
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by Pierre86

biwa wrote:
Tue May 05, 2020 6:52 am
Interesting, how does that work? Why crank length affects gear ratio? I thought gear ratio is completely dictated by chainrings and cassette sizes?
The ratio is determined by the gearing but your interaction with that ratio changes with crank length
biwa wrote:
Tue May 05, 2020 6:49 am
Pierre86 wrote:
Tue May 05, 2020 6:06 am
Main con is percieved lack of torque when climbing or during hard efforts.
Otherwise there's not that much in it and you'll get used to any changes reasonably quickly.
So it's preceived reduction in torque, not an actual reduction? I think I've read somewhere with shorter cranks you need to increase cadence to maintain the same power?
Your cadence will increase, the lack of torque is you have less leverage if you attempt to turn the same gear but really you should be spinning a slightly smaller gear for the same effort.
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AJS914
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by AJS914

This link has a lot info - explains it way better than I could.

https://www.slowtwitch.com/Tech/Crank_L ... _4095.html

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jekyll man
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by jekyll man

Pierre86 wrote:
Tue May 05, 2020 6:53 am
alcatraz wrote:
Tue May 05, 2020 6:47 am
Shorter cranks can't be more efficient during acceleration. Track riders don't have gears. Can it be related?

I'd summarize short cranks as efficient for sustained efforts and for people with injuries. But I'm not a doctor...

Track sprint is as far removed from road as you can get, other than it being on a bike there is very little carry over between the two. Short cranks are better for track sprinting but for various other reasons
There's a very real risk of long cranks bottoming in the bends depending on the length of the track for sure.

Also it's generally been found you need to up the gear when going shorter, think there's a good post from Steve cobb somewhere about it.
Provided everything else remains the same fitwise, power won't magically increase or decrease.
FWIW i traditionally ran 172's as that's what my first decent road bike came on, but my current crop have 165, 170, 172, and my mtb has 175 but they're a different kettle of fish.
Other than a slight stunting of the pedal orbit , you won't notice any difference
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