Advantages/disadvantages of shorter crank arms?

Discuss light weight issues concerning road bikes & parts.
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Noctiluxx
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Location: Southern California

by Noctiluxx

I just ordered a Dura Ace 9170 groupset with 165mm crank arms for my Cervelo R5 disk. I'm 170cm tall and all my other road and gravel bikes have 170mm crank arms. To be honest the compact 9100 crank with 170mm arms was out of stock making decision a bit tough for me. I didn't want to go up to the available 172.5 so I decided to roll the dice and try the 165mm. I'm aware the advanatges of using shorter arms for TT/Tri bikes but what about road bikes?
2018 Bianchi Oltre XR4, (Celeste Matt)
2018 De Rosa SK Pininfarina (Blu)
2019 Trek Madone SLR (Rage Red)
2019 Giant TCR Advanced SL (Chameleon Blue)
2019 Cervelo R5 Disk (Team Sunweb)
2019 Giant Revolt Advanced 0

Hexsense
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Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Same advantage and disadvantage as in TT.
I'm 169cm and using 165mm crank on all my bikes. If pro racers 186cm tall using 172.5mm crank. Us, 165-172cm rider using 165mm crank is actually using a very long crank in comparison to the height.

Advantage: higher effective gear.
-shorter crank has smaller circle. For the same linear foot speed, you cover more circles. So your average and max cadence is going up, effectively give you extra max speed.

Disadvantage: higher effective gear.
-shorter crank has less leverage, so lower torque output (feel like you are on a 0.5 gear higher). This means at the end of the low gear range, where you can't shift down anymore, that gear can feel harder. (compensate this by using cassette or chainring with lower gear ratio).

The other advantages such as better bio-mechanical efficiency, open up more hip angle for more aero position etc. are obvious. I think you can read everywhere.

by Weenie


TobinHatesYou
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by TobinHatesYou

I'm 178cm and use 165mm cranks and would consider 160mm cranks if more options were available. In addition to what's already been mentioned, I can pedal through corners at slightly more aggressive angles which is a huge boon when trying to be as efficient as possible in crits.

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wheelsONfire
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by wheelsONfire

Perhaps it's a learning curve, i tried 170mm and 175mm. 175mm was horrible. 170mm felt good, but i think i pedalled so i yanked the bike.
But i sometimes think that when on the, upstroke, it would be a great advantage. All my cranks are 172.5mm versions.
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

dudemanppl
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by dudemanppl

I'm the same height and went from 172.5 to 170 to 165 to 150. First ride on it will feel weird but afterwards feels just like riding a normal bike. I have a slight hip inpingement issue and 150 cranks are great and I'm still able to hit the same max power, although you have to focus on pedalling technique more with a short crank while sprinting.

RossLB
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Joined: Sun Oct 21, 2018 7:18 am

by RossLB

I'm a similar height and recently went from 170mm to 165mm cranks on all my bikes. The main reason was to try to prevent some intermittent knee pain, and that seems to have been successful. I now prefer the 165mm cranks, and have found no real difference in power output, but it does feel more comfortable for my relatively shorter legs.

Remember to raise your saddle 5mm to compensate.

g32ecs
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by g32ecs

I've been using 165/167.5 since I started back in 2012. I'm about 168cm

I don't know much about using a longer crank on the ROAD, but my Fatbike has 175mm and use it primarily on a flat gravel trail. Take me out on a hilly route and my cadence decreases heavily.

On road I'd average about 90rpms and have built my power with high cadence. That's the benefit for me primarily.

Con for me: I cant produce power at a lower cadence. Im not sure if that has something to do with leverage.

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Lewn777
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by Lewn777

I'm 182cm but short in the leg long torso. I use 172.5cm, tried 175 a bit too long, 170cm were too short an spinny. 172.5 feels perfect to me. Although I set my bike up for all day mountain fondos. If I was doing hill climbs or crits I might rethink things and experiment with 170cm.

TobinHatesYou
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by TobinHatesYou

Depends on the hill climb. If you're competing in short, punchy hill climbs, you're probably going to be out of the saddle. That means hip impingement isn't really an issue. You'd also want the additional leverage since you'll be up in Z6/Z7 power. For a longer, shallower climb, then yes short cranks all day.

NickJHP
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Location: Canberra, Australia

by NickJHP

I'm 178cm and have used at various times 165, 170, and 175 on the road, and can't say that I really notice the difference. At the moment my bikes are split about 50/50 between 165 and 170, and in a blind test I don't think I'd be able to pick what length was what.

TobinHatesYou
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by TobinHatesYou

NickJHP wrote:
Wed Jan 01, 2020 6:35 am
I'm 178cm and have used at various times 165, 170, and 175 on the road, and can't say that I really notice the difference. At the moment my bikes are split about 50/50 between 165 and 170, and in a blind test I don't think I'd be able to pick what length was what.

Yep. Same height, same experiences. Madone has 170s, Emonda has 165s and my trainer shitbike has 172.5s. I can't really tell the difference by feel, but when I ride the 165s I have more confidence in pedaling through corners.

Nefarious86
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by Nefarious86

Corners, The exact reason ill go to 170mm on the next bike.

Im 189cm tall and run 172.5 on the road and 170 on the tt.

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stoney
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by stoney

I'm 177.8cm with short legs and converted my MTB from 175mm to 170 and it is a big improvement for me. My road bike is currently 172.5mm and it feels ok but in the future I plan on converting it to 170mm as well. I think having all my bikes with the same crank length would be better to maximize my training for road and MTB racing as I split my training about 50/50 between road and MTB.

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slake21
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by slake21

I'm 191cm and have 175s
they feel a bit "more right" for me after the previous 172.5 set

by Weenie


alanyu
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by alanyu

Height is not important but your leg length and the even the proportion of your thigh and calf is.

I'm 80 inseam. I've tried 170, 172.5 and 175.

In a blind test, I can definitely tell you which length I'm riding with. 175s are not suitable for me as my knees feel very bad at either the top dead point or the bottom dead point, even both, depanding on the saddle height. 172.5s lower my cadence from ~100 with 170s to ~90, but I feel more comfortable while climbing and I can hold longer time with higher output on a steep hill. Now I'm having 170s on my road bike and pedaling is smooth. I feel better with 170s than 172.5s on flat. I've never tried shorter ones.

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