Crank length

General cycling advice ( NOT technical ! )
Debs
Posts: 774
Joined: 19 May 2017, 7:05pm
Location: Powys

Re: Crank length

Postby Debs » 23 Jan 2020, 11:14pm

PT1029 wrote:A friend in our local CUK group has 170/172.5/175 mm cranks on his 3 bikes, says he doesn't notice any difference.
I am used to 170 mm cranks. When building up a mountain bike (which later morphed into a camping/poor tarmac tourer) in the 1990's I was told mountain biking, best use 175 mm cranks (a new thing then).
While I could use 175 mm cranks without issues, I just couldn't get on with them, as the saddle simply felt too low*, so I replaced them with 170 mm cranks, and found them much better (for me at least).


My 1996 Gary Fisher Aquila is a typically 90s mountain bike equipped with 175mm cranks, i frequently used it as an urban street machine. I never noticed any concern over crank length while using it around the hilly town where i used to live, but i think this is because the rides were fairly short; 2 miles into town, 1 or 2 miles ambling around and 2miles to get back home again = just 5 or 6 miles, and riding uphill felt nice to have the extra leverage of the longer cranks, and around the rest of these urban excursions the cadence is naturally a lot lower than typical out-of-town mile crunching type riding, plus much freewheeling downhill or in traffic conditions. In other words, on rides where cadence can be lower for reasons of town traffic and junctions, one is not going to experience any obvious problem with crank lengths being a bit too long.

So my Aquila is okay for urban trips, shopping, and socialising around the town, however since moving to a new countryside location i've found it unpleasant to ride over longer distances where one wants to exercise ones 'natural cadence' but feels uncomfortable when trying to do this with a longer crank length, the other problem is the straight handle bars which again are fine on short urban trips but on longer rides i prefer drops so i can vary my hand position - but that's another story :)

Still got the Aquila, maybe one day i'll change the chainset to one with a 170mm crank, and convert it to drops :D

Image

niggle
Posts: 3423
Joined: 11 Mar 2009, 10:29pm
Location: Cornwall, near England

Re: Crank length

Postby niggle » 25 Jan 2020, 7:04am

Brucey wrote:one of my chums used 170mm cranks for years, tried 175mm and found it made his knees hurt, then changed to 172.5mm and has been happy ever since.

To my annoyance many years ago I found I'd become habituated to 6-5/8" cranks, which you can't buy these days. 170mm is just a few mm longer but enough to be felt.

cheers

6&5/8" is 6.625" which is 168.275 according to Google, so have you tried 167.5mm cranks?

CathM
Posts: 12
Joined: 1 Nov 2019, 5:20pm

Re: Crank length

Postby CathM » 26 Jan 2020, 9:10pm

Brucey wrote: "I've even known folk ride for years with cranks that are different lengths each side and not notice."

Many years ago I bought a second-hand touring bike, after checking it (inexpertly) for the usual faults; it never occurred to me to check that the cranks were the same length. I rode it for about a year before a nosy friend (now husband) pointed out that my cranks were too long for me, being 175mm long; I was able to tell him after a closer look that he was half right; one of them was 170mm! I didn't detect a difference in crank length while riding but what did puzzle me was that I could never get my saddle height quite right, no matter how much I adjusted it. I have since changed all my bikes to 165mm cranks (I'm 5 ft 6") and that's made all the difference to my knees. So if buying second-hand, check that the cranks are a matching pair!

niggle
Posts: 3423
Joined: 11 Mar 2009, 10:29pm
Location: Cornwall, near England

Re: Crank length

Postby niggle » 27 Jan 2020, 12:49pm

CathM wrote:Brucey wrote: "I've even known folk ride for years with cranks that are different lengths each side and not notice."

Many years ago I bought a second-hand touring bike, after checking it (inexpertly) for the usual faults; it never occurred to me to check that the cranks were the same length. I rode it for about a year before a nosy friend (now husband) pointed out that my cranks were too long for me, being 175mm long; I was able to tell him after a closer look that he was half right; one of them was 170mm! I didn't detect a difference in crank length while riding but what did puzzle me was that I could never get my saddle height quite right, no matter how much I adjusted it. I have since changed all my bikes to 165mm cranks (I'm 5 ft 6") and that's made all the difference to my knees. So if buying second-hand, check that the cranks are a matching pair!

I am also 5'6" and 165mm is best for me was well, though I do have 170mm cranks on a couple of bikes, for which getting the saddle well back also helps to some degree.

Marcus Aurelius
Posts: 1584
Joined: 1 Feb 2018, 10:20am

Re: Crank length

Postby Marcus Aurelius » 27 Jan 2020, 1:29pm

I find the 170mm cranks make for a less tiring ride, if I’m going for a distance ride. It’s most noticeable in the bits of the muscles nearest the knees, and the ankles for me. I don’t notice the difference so much, if it’s just a utility / shorter / jolly type ride.