? 175 vs. 172.5 crank arm length

Discussion in 'Cycling Equipment' started by Mmcs, Mar 10, 2003.

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  1. Mmcs

    Mmcs Guest

    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?
     
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  2. 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
     
  3. Ted Bennett

    Ted Bennett Guest

    > 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
     
  4. A Muzi

    A Muzi Guest

    "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
     
  5. 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
     
  6. Jay Beattie

    Jay Beattie Guest

    "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.
     
  7. Tim McNamara

    Tim McNamara Guest

    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.
     
  8. Andy Coggan

    Andy Coggan Guest

    "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
     
  9. Jay Beattie

    Jay Beattie Guest

    "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.
     
  10. Andy Coggan

    Andy Coggan Guest

    "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
     
  11. Bluto

    Bluto Guest

    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
     
  12. Ted Bennett

    Ted Bennett Guest

    > > 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
     
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