Yes. Another crank length question.

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1982john
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Yes. Another crank length question.

Postby 1982john » 15 Sep 2018, 7:20pm

So this summer I've got back into touring but I'm finding a limiting factor is sore muscles mainly above my knee. It's not I can't ride pain but more just feeling heavy.

This is probably just down to my own lack of fitness but I do wonder if should be using shorter cranks. I'm 5ft 5 and looking at various blogs they say a good calc to follow is inseam * 2.16 which gives about 160mm and I'm currently using 170mm

Problem is 160mm seems quite hard to find. I could go to 165mm but I'm not sure if that would make much difference?

Have other people dropped down with success?

Brucey
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Re: Yes. Another crank length question.

Postby Brucey » 15 Sep 2018, 7:43pm

the preference to any given crank length is only very weakly related to leg length, and is subject to the vagaries of fashion amongst other things.

I'd suggest that before concluding that you have the wrong length cranks (which if you change to a non-standard length makes bike-buying a complete misery for ever after BTW), you take some advice about what the true origin of your discomfort is.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

brynpoeth
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Re: Yes. Another crank length question.

Postby brynpoeth » 15 Sep 2018, 8:10pm

Brucey wrote:the preference to any given crank length is only very weakly related to leg length, and is subject to the vagaries of fashion amongst other things.

I'd suggest that before concluding that you have the wrong length cranks (which if you change to a non-standard length makes bike-buying a complete misery for ever after BTW), you take some advice about what the true origin of your discomfort is.

cheers

Really? Normal heights for adults (m/f) go from 150 cm to 200 cm
I submit that most people are using cranks that are too short or too long

Alternative facts welcome
..
In the case of the OP one could just try lowering the saddle
Last edited by brynpoeth on 15 Sep 2018, 8:50pm, edited 1 time in total.
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fausto copy
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Re: Yes. Another crank length question.

Postby fausto copy » 15 Sep 2018, 8:19pm

I'm 5' 6" and I use 165mm cranks on all three solos (don't ask :oops: ) which I find suit me better than 170mm's.

grufty
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Re: Yes. Another crank length question.

Postby grufty » 15 Sep 2018, 8:38pm

I'm 5' 9"" and Mrs Grufty is 5' 6"". I changed all our cranks to 160 last year, not all at once- my Troll was the guinea pig but as soon as Mrs Grufty tried it she wanted the same!
We've both got an arthritic knee, so it made spinning a lot easier. Mrs Grufty had a TKR 5 weeks ago, was on the turbo within a week, the brommy within 2 and is now back on her cumbersome!
Spa and SJS do a range of crank lengths, I've had stuff from both, but we don't do derailleurs so that probably makes it easier.

brynpoeth
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Re: Yes. Another crank length question.

Postby brynpoeth » 15 Sep 2018, 8:51pm

Should one change the saddle height when fitting shorter cranks?
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grufty
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Re: Yes. Another crank length question.

Postby grufty » 15 Sep 2018, 8:53pm

We went a bit higher, yes.

Brucey
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Re: Yes. Another crank length question.

Postby Brucey » 15 Sep 2018, 10:08pm

brynpoeth wrote:
Brucey wrote:the preference to any given crank length is only very weakly related to leg length, and is subject to the vagaries of fashion amongst other things.

I'd suggest that before concluding that you have the wrong length cranks (which if you change to a non-standard length makes bike-buying a complete misery for ever after BTW), you take some advice about what the true origin of your discomfort is.

cheers

Really? Normal heights for adults (m/f) go from 150 cm to 200 cm
I submit that most people are using cranks that are too short or too long

Alternative facts welcome
..
In the case of the OP one could just try lowering the saddle


yes really. Anyone interested in this topic should take a very careful look at the research before changing without good reason, and/or assuming that there is a good fixed relationship between leg length and crank length.

If you plot leg length against preferred crank length (amongst skilled cyclists) or crank length at optimum power output vs leg length you don't get straight line plots or anything close to it. In each case you get a 'splodge' through which you can (if you are deluded) draw a straight line, apportion it a slope and come up with a 'formula'.

Folk will unwittingly follow 'the formula' even though its predictions actually have error bars that span almost the full range of available cranks..... :roll:

Habituation and/or apparently random preference is far more important than leg length per se and folk with medical issues often change (one way or the other) and say they prefer it. Fashions change; about a hundred years ago much longer cranks were the vogue; folk of medium height would often use 8 or even 9-inch cranks.

Recumbent riders and HPVers often use shorter cranks than normal. The latter have a very good reason, being that the length of the cranks defines the size of the pedal box and that defines the aerodynamic performance of the machine. Obviously you need to push harder and/or spin faster on shorter cranks to generate any given amount of power.

BTW I got habituated to 6-5/8" cranks in my youth and it took me a very long time (years) before I felt I pedalled anywhere near as nice circles on 170mm cranks. The length difference is less than 2mm. One of my chums has (in recent years) increased his crank length by 2.5mm and now doesn't enjoy riding his 'training bike' on the old length cranks.

On the other hand some folk say that they don't even notice a 5mm change, but that doesn't mean that they mightn't go faster/easier on one length than another, without noticing.

cheers
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Bowedw
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Re: Yes. Another crank length question.

Postby Bowedw » 16 Sep 2018, 8:16am

I am about 5' 5'' and bought a used bike with 160 cranks 8 yrs ago. Just rode it a couple of 100 yards and thought these kiddie cranks have to go and changed them for 170's.
Fast forward about 4 years I tried the 160's on another bike and went for a decent ride. I came to the conclusion that I went better and dare I say it faster and my legs felt much better afterwards.
Since then I have changed all my bikes to 165's as I could not get the old idea that longer cranks where the way to go. On reflection I am a little sorry I did not go for the 160's.I may even go that way in the future as long as Spa cycles are still stocking their excellent range.

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Cugel
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Re: Yes. Another crank length question.

Postby Cugel » 16 Sep 2018, 9:30am

As Brucey notes, "correct" crank length is more a matter of habituation or fashion than anything determined objectively from data about pedalling efficiency against height or leg length.

Moreover, there are alternative theories, most notable of which is that of Mike Burrows, who is so fervent in his belief that much shorter cranks are better, he offers a service to drill new pedal 'oles part-way down the crank! (Or he did do - don't know if he still does).

Personally I don't mind and can't tell the difference between 165mm and 175mm - the usual range offered. However, there is something to be said for shorter cranks if they mean that the reduced pedalling circle means you don't catch your toe-end on the front wheel whilst pedalling a slow tight turn, when you did with longer cranks. But that's a very small consideration unless you're a trick cyclist.

Cugel

1982john
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Re: Yes. Another crank length question.

Postby 1982john » 16 Sep 2018, 9:48am

Cugel wrote:As Brucey notes, "correct" crank length is more a matter of habituation or fashion than anything determined objectively from data about pedalling efficiency against height or leg length.

Moreover, there are alternative theories, most notable of which is that of Mike Burrows, who is so fervent in his belief that much shorter cranks are better, he offers a service to drill new pedal 'oles part-way down the crank! (Or he did do - don't know if he still does).

Personally I don't mind and can't tell the difference between 165mm and 175mm - the usual range offered. However, there is something to be said for shorter cranks if they mean that the reduced pedalling circle means you don't catch your toe-end on the front wheel whilst pedalling a slow tight turn, when you did with longer cranks. But that's a very small consideration unless you're a trick cyclist.

Cugel



I find it hard to accept that crank length doesn't make a difference and is just a fashion thing. I've not read any studies (are there even any around?). But if you take the extreme at both ends say a 180mm vs 160mm I would expect to see a noticeable performance difference. Part of the problem with cranks is that the range available is so dismal. There's probably more variation in stem length!

You say you don't notice any difference between 165 and 175 but you don't say your height. If you're short then going into any sort tuck position means your legs hit your torso with longer cranks.

Anyway I do agree with what I think you and others have implied in that I'm just guessing that shorter cranks might help and I totally agree with that. I would need some sort of expensive bike fit analysis (£100?!) to get that information.

fastpedaller
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Re: Yes. Another crank length question.

Postby fastpedaller » 16 Sep 2018, 10:12am

Without any real data surely no 'rules' can be established that are meaningful. How is that data gathered without some 'adaption period' as just leaping from short cranks to long cranks, and maybe back again :roll: without the body adapting to it won't give conclusive 'proof'. For some while I time-trialled on a road/track bike with fixed wheel and 150mm cranks - right up to 12 hrs. Whether the cranks helped or hindered I've no idea, but if I changed to a bike with 'regular' 170mm cranks it felt very odd at first. I'm riding 160 's all the time now on a single (not fixed) or my geared bike, and don't even think about it. One things for sure is that there must be a difference (albeit slight?) and there are extremes - I'm sure 300mm cranks (apart from hitting the ground!) would be too extreme, likewise 60mm cranks - somewhere in between lies the ideal for all of us :wink:

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Cugel
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Re: Yes. Another crank length question.

Postby Cugel » 16 Sep 2018, 1:31pm

1982john wrote:
I find it hard to accept that crank length doesn't make a difference and is just a fashion thing. I've not read any studies (are there even any around?). But if you take the extreme at both ends say a 180mm vs 160mm I would expect to see a noticeable performance difference. Part of the problem with cranks is that the range available is so dismal. There's probably more variation in stem length!


What would make the performance difference? A longer crank is a longer lever and for the same applied force of the foot might develop more power. But to do so your leg will have to flex over a greater range, which requires more work over the same period of one rev. (I think).

In all events, whatever theory you can come up with, there are various perms of leg length and crank length going about but no one I know of has demonstrated a formula for best combination to give most efficiency from measured evidence in a controlled experiment that's been repeated enough times by enough experimenters to be convincing. Even the Burrows lad seems to have just the theory and his own (unrepeated, as far as I know) "test results" that indicate shorter cranks are more efficient.

1982john wrote:You say you don't notice any difference between 165 and 175 but you don't say your height. If you're short then going into any sort tuck position means your legs hit your torso with longer cranks.


5ft 10ins with a 32in inside leg. When I were a racing lad with me nose glued to the front wheel (not literally) I had no bang o' the knee into the rest of me, even with 175mm cranks. I suppose you could manage it if you get very, very low and very, very flat-backed. In practice...... wouldn't you just raise your torso a bit? But I've not heard of this occurring.

1982john wrote:Anyway I do agree with what I think you and others have implied in that I'm just guessing that shorter cranks might help and I totally agree with that. I would need some sort of expensive bike fit analysis (£100?!) to get that information.


Bike fits, especially the expensive kinds, contain all their own assumptions bordering on prejudices, about "correct" postures. You can do your own highly effective bike fit by riding about at various levels of effort, over various terrains, and listening to your body. Once upon a time, before someone commodified everything in the world, we all did that.

Cugel.

brynpoeth
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Re: Yes. Another crank length question.

Postby brynpoeth » 16 Sep 2018, 4:33pm

What length cranks do our three Grand Tour winners use? If marginal gains are to be had..
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Thornyone
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Re: Yes. Another crank length question.

Postby Thornyone » 16 Sep 2018, 6:29pm

I'm 5'6'' but much more significantly I have rather short legs even for that height. However, my crank length is 170mm and does not seem to cause me problems. Much more of a problem, I would imagine, is the very low saddle height that a lot of people who are a good deal taller than me seem to adopt. (Not suggesting for a minute that the OP rides like this, just something I notice, along with people riding with their heels on the pedals :roll: )