Crank Length

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Stradageek
Posts: 912
Joined: 17 Jan 2011, 1:07pm

Crank Length

Post by Stradageek »

My wife at 4'10" has always looked 'awkward' on any bike she rides. Eventually her day to day commuter became an ancient three-speed folder with cottered cranks. This both looked, and to Jean felt, the most comfortable ride.

I noticed that the cranks were only 150mm long so fitted 160mm cranks to her Dawes tourer - 160mm being the shortest I could find on a standard triple from a child's bike. The Dawes still wasn't comfortable.

I then discovered this https://highpath.co.uk/crank-length-calculation/ which estimated she needed 135mm cranks!

We purchased some crank shorteners and fitted them to her Kettwiesel trike using the nearest 130mm option. This shortened the cranks by 25%.

Her cycling experience is reborn! No more aching hips, no more struggling to push off and much faster overall as a much more comfortable higher cadence, is not only possible but preferred.

Interestingly, I imagined I'd have to reduce the bikes gearing to compensate but as Jean can now put optimal power in over the whole pedal stroke no changes have proved necessary.

So it strikes me that whereas much progress has been made with women's frame sizes, reach etc.a lot more should be done to make genuinely 'short' cranks available
Halla
Posts: 194
Joined: 27 Apr 2008, 9:28pm

Re: Crank Length

Post by Halla »

Have you looked at the SPA Cycles website?

They have crank lengths from 130mm right through to normal adult sizes in 5mm increments..

The shorter cranks are shown as kid cranks, seem to be for double chain rings.
Stradageek
Posts: 912
Joined: 17 Jan 2011, 1:07pm

Re: Crank Length

Post by Stradageek »

I think my beef is with the bike designers. By my approximate calculations, any bike designed for a small person (say 5'2" - 5'4") should be fitted with 150mm cranks as standard with options to go shorter.

This blind spot in bike design ranks alongside the obsession with over-gearing. I've lost count of the number of bikes I've repaired that have a completely unused 'big' ring - why does a hybrid need a 120" gear!

My first change to my lovely Pashley Postie cargo bike was to fit a small chain ring. With the original ring I can't imagine any postman tackling even a modest slope - no wonder they were always pushing them :D
Bmblbzzz
Posts: 4067
Joined: 18 May 2012, 7:56pm
Location: From here to there.

Re: Crank Length

Post by Bmblbzzz »

It's good to hear this story. :D I'd agree that by and large there's a tendency to both over-crank and over-gear most bikes.
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531colin
Posts: 13785
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Crank Length

Post by 531colin »

Stradageek wrote: 5 Jun 2021, 8:15am I think my beef is with the bike designers. By my approximate calculations, any bike designed for a small person (say 5'2" - 5'4") should be fitted with 150mm cranks as standard with options to go shorter.

This blind spot in bike design ranks alongside the obsession with over-gearing. ............
Tell you what.....you source the cranksets with crank length 150mm and shorter and a BCD less than 74mm.....and I'll design the bikes!

The Stronglight Kid cranks are doubles 110/74 BCD.......minimum ring size is 34, which is absurd for a touring bike.
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