Author Topic: Crank length  (Read 3620 times)

Crank length
« on: September 04, 2009, 09:19:13 am »
Just wandered what others' opinions are here on crank length.  I looked back through and couldn't find much on this board.

I've got 170mm which came on the B2.  I'm just under 6ft, so didn't expect this to be an issue, but I do have a relatively longer body and shorter legs.  Got a tiny bit of knee ache at first after I was pushing in higher gears, but put that down to over-eagerness.  I'm now up to about 2 months ~800km, I know about spinning, but I'm still finding some ache unless I keep the torque quite low.  

I've experimented a fair bit with boom length and foot inward/outward angle.  I think I've reached an optimum there (definitely got some improvement), but the issue hasn't gone away entirely.

I know there's information out there on the web, really I'm asking for personal experience of anybody on here who's tried short cranks.  (I could ask Dtek if I can have a try on shorter cranks; but I'm trying to avoid commiting to spending more money when I'm not sure, so I'd like some of your experiences)

clarion

  • Tyke
Re: Crank length
« Reply #1 on: September 04, 2009, 09:23:37 am »
We've had a general (ie not just Darkside) discussion of crank length, informed by Burrows' article in Cycle - last year, was it? - where he was quite evangelical about shorter cranks.

EDIT: Can't find it.  Maybe it was elsewhere.  There's a mention of his article in a discussion of pedalling technique, tho I think that was mainly about dfs. :-\

Carry on ;D
Getting there...

Mr Larrington

  • A bit ov a lyv wyr by slof standirds
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Re: Crank length
« Reply #2 on: September 04, 2009, 10:15:22 am »
I haven't tried short cranks myself, partly because replacing at least three, if not all seven, sets would leave me considerably poorer and partly because I can turn 170s at 100+ rpm all day anyway.  However, many of my Sith mates use them and reckon they do Good Thins for knee problems.  Most people seem to go for ~150-155 mm though a few ruthless iconoclasts have gone down as far as 110 (Rob Hague tried 75mm and reported that it was Silly).
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Satisfying the Bloodlust of the Masses in Peacetime

Re: Crank length
« Reply #3 on: September 04, 2009, 01:37:38 pm »
I went from my usual 170 to 155mm and didn't like it - they lacked leverage when going uphill slowly in low gears, and didn't seem to me to have any particular benefits.

However, your mileage may vary, and some people do advocate short cranks specifically for recumbents on the basis of the different motor unit recruitment patterns of the recumbent pedalling position (or something). So I'm afraid it's suck-it-and-see, or remain curious.

If you've got (or can get cheaply) the right pair of 175s, Mike Burrows can cut them down to 150mm for about £25.
Profit or planet?

clarion

  • Tyke
Re: Crank length
« Reply #4 on: September 04, 2009, 01:44:06 pm »
I bought some 172.5s at Mildenhall for this purpose, but I found some already cut down to 155 anyway.

Not sure what to do with a Campag triple now... :-\
Getting there...

Re: Crank length
« Reply #5 on: September 04, 2009, 02:02:31 pm »
Was it a new triple? 30/40/52? Square taper? I might give it a home.
We are making a New World (Paul Nash, 1918)

clarion

  • Tyke
Re: Crank length
« Reply #6 on: September 04, 2009, 02:04:34 pm »
Used, and 52/42/um, about 30 IIRC...

Square taper, yes.
Getting there...

Re: Crank length
« Reply #7 on: September 04, 2009, 02:06:01 pm »
Assuming the rings are in reasonable codition, what would you take for it?
We are making a New World (Paul Nash, 1918)

clarion

  • Tyke
Re: Crank length
« Reply #8 on: September 04, 2009, 02:11:45 pm »
YHPM
Getting there...

Re: Crank length
« Reply #9 on: September 04, 2009, 10:24:05 pm »
Got some 150s that it looks like Mike cut down on a Burrows SL, on the basis it's my first 'bent I can't be sure what is crank length and what is part of the whole lieing down thing.

Find that the gearing is making sense, can't work out of it could have a lower gear. Not too sure if it would be easier pulling away with longer cranks.

I know it's strange going back to the upright, and the cranks are a big part of that now.

Re: Crank length
« Reply #10 on: September 04, 2009, 10:27:44 pm »
If you've got (or can get cheaply) the right pair of 175s, Mike Burrows can cut them down to 150mm for about £25.

Thanks, I hadn't realised that.  I only knew of Highpath engineering, who seem to be in flux from their website.  You got a link or contact details for Burrows? my google foo is failing me.

Hmm, could try that fairly cheap, but it'd still be ~fifty quid which could go towards nicer cranks instead if I was feeling more decisive.

rwa.martin

Re: Crank length
« Reply #11 on: September 06, 2009, 01:09:09 pm »
I fitted 150mm cranks to my Bacchetta Giro 20. I have an xseam of 42" and am 5'11" tall. I reckon they make a big difference for me. I probably don't generate as much maximum torque but there is more torque available for a greater proportion of the crank revolution (if you see what I mean). This is because I'm not bending the knee so much at the top of the stroke which in turn means I'm putting power into the pedal, not the knee.
My guess is that everyone has an optimum crank length below which there is no gain, just loss of torque.
My cranks came from SJS and use a square taper bottom bracket. Rings from Spa cycles (24/34/44). 110/74 bcd .
Rich.


recumbentim

  • Only 6 SR,s No hyper yet
Re: Crank length
« Reply #12 on: September 06, 2009, 07:59:38 pm »
GO TO,  recumbent crank length calculator,  and be totally baffled. I was???

Re: Crank length
« Reply #13 on: September 07, 2009, 11:26:24 am »
I fitted 150mm cranks to my Bacchetta Giro 20. I have an xseam of 42" and am 5'11" tall. I reckon they make a big difference for me. I probably don't generate as much maximum torque but there is more torque available for a greater proportion of the crank revolution (if you see what I mean). This is because I'm not bending the knee so much at the top of the stroke which in turn means I'm putting power into the pedal, not the knee.

Thanks, that's very useful.  I'm about 5'11', around 43" xseam.

My guess is that everyone has an optimum crank length below which there is no gain, just loss of torque.

I have a slight suspicion of this too, though I just spoke to Mike Burrows on the phone and he says even shorter is fine, but I was expecting that.   :)

I'm getting the cheapy cranks shortened to 150, will use that for a while and see how I get on.  If it works well I might get the SJS ones with length and rings chosen depending on results with these.

Re: Crank length
« Reply #14 on: September 07, 2009, 11:29:11 am »
GO TO,  recumbent crank length calculator,  and be totally baffled. I was???

Indeed, just a little difficult to measure those lengths with any accuracy.   :-\

I think I want about 140 according to that, but it depends where I estimate my hip joint centre of rotation is.   I'm not dismantling it to check.   :hand:

recumbentim

  • Only 6 SR,s No hyper yet
Re: Crank length
« Reply #15 on: September 07, 2009, 08:34:32 pm »
Yes i am on 170 s , i,m 6"2 and it say,s thats ok with  low cranks . I got Bacchetta with  high cranks so sould prob be on less length.
Ever body wil be lookin now and gettin confused. But mr Burrows will know???