Short Cranks
Printed From: BHPC Forum
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Forum Name: Building
Forum Description: Anything to do with building HPVs
URL: https://forum.bhpc.org.uk/forum_posts.asp?TID=5229
Printed Date: 27 March 2026 at 4:34am
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Topic: Short Cranks
Posted By: mark aldridge
Subject: Short Cranks
Date Posted: 15 December 2015 at 6:17pm
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Due to incipient decrepitude I am finding MTB ratios more usefull than road ones. Can anyone advise on a good quality lightweight crankset that will be suitable for shortening to 150mm. I have used up all the old ones from my store cupboard and reluctantly will have to prise my wallet open (ugh!). Thanks Or does anyone have a suitable one they want to sell.
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Replies:
Posted By: Highpath
Date Posted: 09 April 2016 at 8:07am
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In our experience SRAM solid aluminium cranks are generally good for shortening. Patrick @ Highpath Engineering Ltd http://www.highpath.co.uk - http://www.highpath.co.uk |
Posted By: GeoffBird
Date Posted: 10 April 2016 at 10:46am
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Mark, bear in mind that shorter cranks will effectively raise the gearing, so you should fit smaller chain rings to compensate. ------------- Right Time - Right Place - Wrong Speed |
Posted By: Highpath
Date Posted: 10 April 2016 at 10:47pm
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Logically you would think shorter cranks need lower gearing ..... but feedback I have had from customers for whom we have shortened cranks have reported more power available, so they have stuck with the same gearing. Patrick @ Highpath. |
Posted By: GeoffBird
Date Posted: 11 April 2016 at 12:01am
More power? I wish  ------------- Right Time - Right Place - Wrong Speed |
Posted By: zoxed
Date Posted: 11 April 2016 at 9:27am
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My experience of several years of 140mm cranks is that I needed an equivalent percentage reduction in gearing, which does create problems getting low enough with a 700c rear wheel (406 is much easier !). |
Posted By: mark aldridge
Date Posted: 11 April 2016 at 12:10pm
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I find the short crank question very interesting. It is up there with the helmet question on the CTC website for producing contradicting, controversial and baffling opinions. I am very much a practical results orientated cyclist and as long as it works I am not over worried about how it does it. Using short cranks now feels very natural to me and I am willing to put up with the limited choice or need to cut down existing cranks to keep my knees happy. As it stands the routes are as follows, each with limitations. Run Da Vinci 150mm or TA Carina 155mm off the peg cranks. Low Q factor, multiple spider choices but expensive. Run cheap cranks from the like of ICE and Thorn. Limited choice of gearing, lower quality and heavy. Run kiddy cranks from the likes of Stronglight. Limited choice of gearing, low quality and heavy. Run BMX cranks. Compatibility problems and extremely heavy. Shorten road cranks or MTB cranks. Road cranks (low Q factor) with ability to mount small rings and having solid alloy arms are rare, mostly old TA ones. MTB cranks (higher Q factor) are easier to find but the minefield of hollow arms/carbon arms/extreme profiles/machined channels etc mean that finding a suitable set is difficult. There was a German chap who had all the answers with a semi-custom crank building service (with many lovely anodised options) but his website is inactive and it appears the sums did not add up. Zinn in the USA will also be an option if I win the lottery. It can all be sorted out with a bit of perseverance. Thanks for the advice Mark
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Posted By: speedy381
Date Posted: 11 April 2016 at 8:07pm
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Very informative stuff there Mark, in terms of short crank sources. My feelings on the effectiveness of short cranks are that, from a hardware perspective it depends on your BB height, or hip angle. From a physiology perspective it depends on your hip and leg flexibility, or range of movement. Acceleration and short term power is usually increased, with less inertia and sustained spinning easier. As you say, it is a contentious issue but I often test/demonstrate the effect during my day job as a bike fitter (non-recumbent mostly), using a rig with adjustable cranks. |
Posted By: Neil F
Date Posted: 13 April 2016 at 9:22am
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Some may be interested in this paper: Effect of crank length on joint-specific power during maximal cycling http://custom4.us/wp-content/uploads/2011/08/20110822_2011_msse_cranklenght_jointspecificpowercycling.pdf" rel="nofollow - http://custom4.us/wp-content/uploads/2011/08/20110822_2011_msse_cranklenght_jointspecificpowercycling.pdf Enjoy ;-) |
Posted By: zoxed
Date Posted: 13 April 2016 at 12:19pm
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If you want more links to articles etc then see http://www.zoxed.eu/short_cranks.html" rel="nofollow - http://www.zoxed.eu/short_cranks.html |
Posted By: Highpath
Date Posted: 13 April 2016 at 8:38pm
That's the feedback we've had from customers using shortened cranks on Powertaps  .As above, it depends on many mechanical and biomechanical factors. ------------- www.highpath.co.uk |
GeoffBird wrote: