? 175 vs. 172.5 crank arm length

What is the significance to my training/general riding of pedaling two different bikes one with 175
and the other with 172.5 length crank arms?

 

A shy person askked:

> What is the significance to my training/general riding of pedaling two different bikes one with
> 175 and the other with 172.5 length crank arms?

Precious little. The bike with longer cranks will provide a 1.4% lower gain ratio in a given
sprocket combination, so for the same gear it would climb a wee bit better, but not top out as fast.
Since you presumably have the option of changing gears, this difference, small as it is, becomes
utterly insignificant in practice.

The longer cranks will require you to bend your knee a bit farther for each stroke, possibly leading
to knee problems that a shorter crank might not cause, but, again, this difference is so small it
really doesn't matter.

Sheldon "Long Legs, Short Cranks" Brown +---------------------------------------------------------+
| We can be knowledgeable with other men's knowledge, | but we cannot be wise with other men's
| wisdom. | -- Michel de Montaigne |
+---------------------------------------------------------+ Harris Cyclery, West Newton,
Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts
shipped Worldwide http://captainbike.com http://sheldonbrown.com

 

> What is the significance to my training/general riding of pedaling two different bikes one with
> 175 and the other with 172.5 length crank arms?

None at all.

But you will get other opinions. Ignore them, for I am right.

--
Ted Bennett Portland OR

 

"MMCS" <[email protected]> wrote in message news:BA92A7AE.9D72%[email protected]...
> What is the significance to my training/general riding of pedaling two different bikes one with
> 175 and the other with 172.5 length crank arms?

Lost in the noise. There will most likely be many more noticeable differences between any two given
bikes than the 2.5mm crank length.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

On Tue, 11 Mar 2003, MMCS wrote:
> What is the significance to my training/general riding of pedaling two different bikes one with
> 175 and the other with 172.5 length crank arms?

No difference, provided your knees bend equally well.

Then, here is my own story about crank lengths. I have always used 170mm cranks and I was very upset
to find out that the, still beautiful, used Record pair I had picked up at a shop were 170 and
172.5, respectively. After going back to the shop the seller acknowledged the mismatch and quite
honestly said: 'That's not right. I'll do my best to try to find a good mating pair for you'
(not been able, thus far). Let me add that he is the MOST experienced mechanic, racer himself
upon a time, you can imagine.

Recently I had considered getting those cranks back and install them, differring lengths
notwithstanding. After all, my left knee is much better that the other one and I know it can bend
more and better. I consulted a good friend of mine, an experienced cyclist too, and he said: 'I
wholeheartedly advice you not to'.

Funny how different people would behave differently and suggest so different approches!

Who has got two 170mm cranks for me, anyhow? I would be satisfied with just the spiders, of course.

Sergio Pisa

 

"Sheldon Brown" <[email protected]> wrote in message
news:[email protected]...
> A shy person askked:
>
> > What is the significance to my training/general riding of pedaling
two
> > different bikes one with 175 and the other with 172.5 length crank
arms?
>
> Precious little. The bike with longer cranks will provide a 1.4%
lower
> gain ratio in a given sprocket combination, so for the same gear it would climb a wee bit
> better, but not top out as fast. Since you presumably have the option of changing gears, this
> difference, small
as
> it is, becomes utterly insignificant in practice.

> The longer cranks will require you to bend your knee a bit farther for each stroke, possibly
> leading to knee problems that a shorter crank might not cause, but, again, this difference is so
> small it really doesn't matter.

I know we always trade the same links (with the same equivocal studies) when this issue comes up,
but is there really no good science on crank length? It would seem to me that the range-of-motion
problem you raise would at least get some attention if it really does have the potential for causing
injury. -- Jay Beattie.

 

In article <[email protected]>,
"Jay Beattie" <[email protected]> wrote:

> "Sheldon Brown" <[email protected]> wrote in message
> news:[email protected]...
> > A shy person askked:
> >
> > > What is the significance to my training/general riding of pedaling two different bikes one
> > > with 175 and the other with
> > > 172.5 length crank arms?
> >
> > Precious little. The bike with longer cranks will provide a 1.4% lower gain ratio in a given
> > sprocket combination, so for the same gear it would climb a wee bit better, but not top out as
> > fast. Since you presumably have the option of changing gears, this difference, small as it is,
> > becomes utterly insignificant in practice.
>
> > The longer cranks will require you to bend your knee a bit farther for each stroke, possibly
> > leading to knee problems that a shorter crank might not cause, but, again, this difference is so
> > small it really doesn't matter.
>
> I know we always trade the same links (with the same equivocal studies) when this issue comes up,
> but is there really no good science on crank length? It would seem to me that the range-of-motion
> problem you raise would at least get some attention if it really does have the potential for
> causing injury. -- Jay Beattie.

IIRC the length cranks need to be before causing such an acute bend as to risk knee problems (in an
otherwise healthy knee) is really big. Where did I read that... maybe in the Hinault book? The size
mentioned- wherever I read it- was like 210 mm; and I would imagine that this would be proportional
to the leg length. With my 91 cm inseam, I should be able to ride 180s with no problem. I have a set
in the basement that I need to mount on a bike and see how they are.

 

"Jay Beattie" <[email protected]> wrote in message news:[email protected]...

> I know we always trade the same links (with the same equivocal studies) when this issue comes up,
> but is there really no good science on crank length?

I don't know of anything equivocal about the studies of Martin et al. - and those are essentially
the only true scientific studies of the topic that I am aware of (in part because I never got my
senior honor's thesis published).

Andy Coggan

 

"Andy Coggan" <[email protected]> wrote in message
news:[email protected]...
> "Jay Beattie" <[email protected]> wrote in message
> news:[email protected]...
>
> > I know we always trade the same links (with the same equivocal
studies)
> > when this issue comes up, but is there really no good science on
crank
> > length?
>
> I don't know of anything equivocal about the studies of Martin et
al. - and
> those are essentially the only true scientific studies of the topic
that I
> am aware of (in part because I never got my senior honor's thesis published).

Do you have a link (if there is one). -- Jay Beattie.

 

"Jay Beattie" <[email protected]> wrote in message news:[email protected]...
>
> "Andy Coggan" <[email protected]> wrote in message
> news:[email protected]...
> > "Jay Beattie" <[email protected]> wrote in message
> > news:[email protected]...
> >
> > > I know we always trade the same links (with the same equivocal
> studies)
> > > when this issue comes up, but is there really no good science on
> crank
> > > length?
> >
> > I don't know of anything equivocal about the studies of Martin et
> al. - and
> > those are essentially the only true scientific studies of the topic
> that I
> > am aware of (in part because I never got my senior honor's thesis published).
>
> Do you have a link (if there is one). -- Jay Beattie.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=12183473&dopt=Abstract

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=11990729&dopt=Abstract

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=11417428&dopt=Abstract

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=10828327&dopt=Abstract

Bottom line: alterations in crank length within (and even beyond) the normal range used by
cyclists has no significant effect on either maximal power or submaximal efficiency. Factors other
than performance (e.g., ground clearance, comfort) should therefore take precedence when selecting
crank length.

Andy Coggan

 

MMCS <[email protected]> wrote"

> What is the significance to my training/general riding of pedaling two different bikes one with
> 175 and the other with 172.5 length crank arms?

Almost nil. 1.4% difference in the pedaling circle diameter. It boggles my mind that parts
manufacturers will offer 170mm, 172.5mm, and 175mm cranks, but no 160mm or 190mm cranks.

Maybe they save costs by making them all the same size and just stamping them with different
dimensions-- I am sure no rider could distinguish the difference in a blind test. I'd lay
money on it.

Chalo Colina

 

> > What is the significance to my training/general riding of pedaling two different bikes one with
> > 175 and the other with 172.5 length crank arms?
>
> Almost nil. 1.4% difference in the pedaling circle diameter. It boggles my mind that parts
> manufacturers will offer 170mm, 172.5mm, and 175mm cranks, but no 160mm or 190mm cranks.
>
> Maybe they save costs by making them all the same size and just stamping them with different
> dimensions-- I am sure no rider could distinguish the difference in a blind test. I'd lay
> money on it.
>
> Chalo Colina

You are a cynical man, Chalo. But you are likely right in this case.

However (ah, I love that word), you can get short cranks from the cute little world of kids' bikes,
and long cranks have been made by Bullseye, if memory serves.

There is an exception to the idea that crank length doesn't matter and is not noticeable: for fixed
gear bikes, where 5mm can make a significant difference in how far you can lean in a turn before you
suffer a pedal strike. And suffer is the right word here.

--
Ted Bennett Portland OR