Cyclocross and Gravelbiking (Recreational) This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like :The Dirty Kanza". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

crankset arm length

Old 02-24-20, 02:04 AM
Senior Member
Thread Starter
Join Date: Sep 2015
Posts: 166
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 81 Post(s)
Likes: 0
Liked 8 Times in 8 Posts
crankset arm length

I am going to switch from 2x Shimano 105 to 1x GRX and I will be changing the crankset in the process. I am 178 cm height with 85 cm inseam and my current crank arm length is 172,5 mm. I am wondering if I should stay with that length or try something shorter like 170 mm? I have read that now it is a trend to use shorter crankset arms because it will be better for my knees and will allow me to spin faster. What do you think?
sweetspot is offline  
Old 02-24-20, 06:42 AM
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 19,882
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 414 Times in 317 Posts
I think either would be fine. When I tried 172.5 arms the first time they felt sluggish. Second time I didn't know they were 172 until I had been happily riding them for a year and the person I bought the cranks from pointed it out. Now I ride 175 interchangeably with my preferred length of 170. I really can't tell the difference.

My gravel bike has relatively low high gear and 175mm cranks, so in the Wednesday night race, I have had to spin at a high rate to keep up. I don't find it any harder to spin than on bikes with shorter cranks. The gearing is the thing that protects your knees and lets you spin, not the crank arm length.

Last edited by unterhausen; 02-24-20 at 06:45 AM.
unterhausen is offline  
Old 02-24-20, 07:23 AM
mstateglfr's Avatar
Join Date: Aug 2014
Location: Des Moines, IA
Posts: 10,420

Bikes: '18 class built steel roadbike, '19 Fairlight Secan, '87 Schwinn Prelude, Black Mountain Cycles Monstercross V4, '89 Novara Trionfo, '18 Diamondback Syncr

Mentioned: 94 Post(s)
Tagged: 0 Thread(s)
Quoted: 4067 Post(s)
Liked 1,040 Times in 664 Posts
If you like the 105 crank arms and the reason you are changing the crankset for a reason other than fit, then keep the length.

I am 6'5 and have 170mm cranks on my gravel bike. Later this month I am going to swap them out for a 172.5mm crank because I want to try out different gearing. I got both cranksets because of availability/cost since I have never really cared if they are 170, 172.5, or 175. My main road bike has 175mm. 2 other road bikes are 170mm. My touring bike currently has a 180mm crank because I had it laying around and wanted to see if I liked it or disliked it more than all the other lengths.
Ends up I couldnt care less to all the lengths. 180mm, 175mm, 172.5mm, 170mm - couldnt care less. I turn my legs and they go around in a circle on all of them. If the circle is 340mm in diameter, my legs are fine. If the circle is 360 in diameter, my legs are fine.

I am sure the length of crank arm affects people more when the leg length is shorter since its a greater difference relative to leg length.

Anyway, point of this is- why change if you like the current length? And you may change only to just not find it matters to you.
mstateglfr is offline  
Old 02-24-20, 03:26 PM
Senior Member
chas58's Avatar
Join Date: Jul 2010
Location: Michigan
Posts: 4,258

Bikes: too many of all kinds

Mentioned: 35 Post(s)
Tagged: 0 Thread(s)
Quoted: 947 Post(s)
Liked 198 Times in 159 Posts
I'm your size. For me, it is more RPM dependent.
For my tandem or mountain bike (where I need the torque and leverage) I'm at 175
For my track bike, where I need HP (& high rpm) I'm at 165.

What do you like to do - spin, or mash the pedals?
chas58 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.