Crack Length Formulas: Who's Correct?

Discussion in 'Cycling Equipment' started by 531Aussie, Jun 27, 2005.

  1. 531Aussie

    531Aussie Well-Known Member

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    it's basically this guy: http://www.bsn.com/Cycling/cranks.html (Ed Zimmerman), who presents a traditional view with some very convincing points.....

    verses these guys:

    http://www.cranklength.info/ (Andrew Bradly)
    http://www.zinncycles.com/cranks.aspx (Lennard Zinn)
    http://www.nettally.com/palmk/crankset.html (Kirby Palm)

    ......who also provide some interesting points, but their formulas seem to put people on pretty long cranks:

    thanks
     
    Tags:


  2. Bill Sornson

    Bill Sornson Guest

    [email protected] wrote:

    > AFAIK, the effect of crack length was pegged...

    ^^^^^^^^^^^
    Good thing you post anonymously.

    :-D
     
  3. Bill Sornson

    Bill Sornson Guest

    Bill Sornson wrote:
    > [email protected] wrote:
    >
    >> AFAIK, the effect of crack length was pegged...

    > ^^^^^^^^^^^
    > Good thing you post anonymously.


    D'oh! My bad. Missed it in the Subject: field...

    Nice catch :)
     
  4. Peter Cole

    Peter Cole Guest

    531Aussie wrote:
    > it's basically this guy: http://www.bsn.com/Cycling/cranks.html (Ed
    > Zimmerman), who presents a traditional view with some very convincing
    > points.....
    >
    > verses these guys:
    >
    > http://www.cranklength.info/ (Andrew Bradly)
    > http://www.zinncycles.com/cranks.aspx (Lennard Zinn)
    > http://www.nettally.com/palmk/crankset.html (Kirby Palm)
    >
    > .....who also provide some interesting points, but their formulas seem
    > to put people on pretty long cranks:


    Good question, and one that's not academic to me, being 6'10"/210cm. I
    think Zinn's a ninny, have seen KP's stuff before and wasn't impressed,
    Bradly has a lot to read. From the things I've read to date, varying
    crank length over a pretty large range didn't have any effect on power
    generation according to experiments. This matches my intuition and
    common sense. The economics of custom cranks and the frame geometries to
    accommodate them make me reluctant to just try them out. My hunch is
    they'll be as effective as Biopace.
     
  5. JeffWills

    JeffWills Guest

    Peter Cole wrote:
    >
    > Good question, and one that's not academic to me, being 6'10"/210cm. I
    > think Zinn's a ninny, have seen KP's stuff before and wasn't impressed,
    > Bradly has a lot to read. From the things I've read to date, varying
    > crank length over a pretty large range didn't have any effect on power
    > generation according to experiments.


    I'll ditto Peter's comments about it being a personal thing- I'm
    6-foot-4. I've somewhat standardized around 175mm cranks on both my
    uprights and recumbents. Varying crank length over commonly available
    lengths doesn't *seem* to affect comfort or power. I have no reliable
    data, though.

    Some of the recumbent community is experimenting with radically short
    cranks (down to 100mm), without an apparent reduction in power. Short
    cranks do have their uses in streamliner applications- shorter cranks
    allow for a reduction in fairing size, reducing frontal and surface
    area.

    Jeff
     
  6. Tom

    Tom Guest

    I'm 6'4" and have a standover height of 37". I rode some 170 mm cranks
    and they were sort of irritating because they needed to be spun before
    they felt right.

    I switched to 172.5 and they felt good on my road bike. On my MTB's and
    'cross bikes I run 175's and then when I switched to Compact on my road
    bikes I got 175's there as well. I can SORT of tell the difference but
    I can't tell whether it's my imagination or not.

    On my track bike I tried 165's and that is PURE CRAP! I had to get some
    170's since I was exhausted after 10 miles on the track with those tiny
    cranks.

    I think that it isn't rocket science but neither is it unimportant.
     
  7. Sandy

    Sandy Guest

    531Aussie wrote:
    > it's basically this guy: http://www.bsn.com/Cycling/cranks.html (Ed
    > Zimmerman), who presents a traditional view with some very convincing
    > points.....
    >
    > verses these guys:
    >
    > http://www.cranklength.info/ (Andrew Bradly)
    > http://www.zinncycles.com/cranks.aspx (Lennard Zinn)
    > http://www.nettally.com/palmk/crankset.html (Kirby Palm)
    >
    > .....who also provide some interesting points, but their formulas seem
    > to put people on pretty long cranks:
    >
    > thanks


    With all the answers, just think about this : if you properly keep the same
    saddle to pedal axle distance, then at the top of your pedal stroke, you
    find your thigh a full centimeter higher, if you switched from 170 to 175.
    Your initiating muscle groups change, and the timing changes. Your recovery
    muscle groups work longer, and the timing changes.

    That said, it's up to you to feel whether these real changes improve or
    degrade your pedaling. They may not have much effect, also. But if we know
    that the change of a centimeter in your horizontal extension makes a pretty
    palpable difference, it may well follow that pedal lengths do influence your
    performance.

    Personally, I think they do. Finding which length is your most effective or
    efficient would take a lot of time in each to evaluate. I think Leonard
    Zinn has done some of that work, but he has his own biases, people say.

    --
    Sandy
    Verneuil-sur-Seine
    *******

    La vie, c'est comme une bicyclette,
    il faut avancer pour ne pas perdre l'équilibre.
    -- Einstein, A.
     

  8. > On my track bike I tried 165's and that is PURE CRAP! I had to get some
    > 170's since I was exhausted after 10 miles on the track with those tiny
    > cranks.
    >
    > I think that it isn't rocket science but neither is it unimportant.


    You might have suffered with the 165s simply because you weren't used
    to them. Especially if you were used to 175s, that is a pretty big
    jump... but on the other hand...

    I read an article about a study online (that I can't seem to find now)
    which stated that varying the crank lengths over a wide range had no
    significant effect on power production. The cyclists would simply vary
    their cadence and gearing to achieve the best muscle contraction rate.
    Zinn himself states elsewhere that he is amazed at how well he can
    perform with 100 mm cranks... and these are less than half the length
    that he prefers!

    As far as I know there have been no tests that show a correlation
    between optimum (highest power) crank length and leg length... if there
    were, certainly the proportional crank advocates would be citing them.
    Zinn sort of claims that he has done some recent tests that show this
    but he won't publish the results... instead he points us towards the
    testimonials... and we all know how reliable those are.

    But who knows... maybe Mangus or Axel could be atop the podium in the
    Tour... if only they had 200 mm cranks...

    -Ron Ruff
     
  9. 531Aussie

    531Aussie Well-Known Member

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    The seat height issue is one that's not really addressed adequately by these "proportional" guys (although, Andrew Bradley's stie is so big it could be in there somewhere :) ), especially Kirby Palm, and to me, an effective saddle drop of 1cm (through the top half of the pedal stroke when going up 5mm in crank length) is a LOT, and could result in lower power.

    I mean, I'm only 6ft, with a 35.2" inseam, and according Kriby Palm's formula I'd be going from 175mm cranks to 193mm!!! If I then dropped the saddle by 18mm, I would then effectively be ~36mm lower, relative to the top half (roughly) of the stroke.

    I know what would happen if I dropped my saddle right now by 36mm: I'd be a crap rider!!

    Having said all that, I did give in, and I'm trying 180s, and so far I like them :)
     
  10. 531Aussie

    531Aussie Well-Known Member

    Joined:
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    http://www.nettally.com/palmk/crankset.html

    I also have some problems with Kirby Palm's suggestions.

    First of all, he's no bike rider :p (check him out http://www.nettally.com/palmk/resume.html), he's just a very clever guy with some unbackable theories, so I don't know why people refer to "the Palm factor" as something that's scientifically credible.

    He lists some references, then acknowledges that they are largely invalid, and, like the others, relies on testimonials.

    He doesn't really address the implications of saddle lowering at all, and I especially have a problem with his answer to the possibility of knee injuries caused by the extra flexion at the top of the stroke:
    "The damage done to knees is actually caused by the continuous and repeated application of too much force, and going to a longer crank is a cure for this problem. With a longer crank, a rider can generate the same power at the same cadence with less force. When you are generating a constant amount of power for hours on end, the use of a longer crank results in a lower amount of force being used for those hours on end." Is he suggesting that a longer cranks means you'll ride at the same speed with less output??!!! :eek: Surely the idea of extra leverage would be to put out the same wattage, and enjoy the advantage of higher speeds! No? Otherwise, I don't see the point.

    The assumption by Zinn and Palm that, if 170mm is correct for a 31" inseam, then....yada yada yada.....this is 21.6%, therefore 21.6% is correct for everyone, is just not enough for me, and most of their arguments are based on this (Andrew Bradley's discussion is more balanced). Who says 170, or even 165 is correct for shorter people? Just because it happened for a long time onbviously doesn't make it right!!

    Eh....whatever....:)
     
  11. colnalu

    colnalu Guest

    Sandy wrote:
    > 531Aussie wrote:
    > > it's basically this guy: http://www.bsn.com/Cycling/cranks.html (Ed
    > > Zimmerman), who presents a traditional view with some very convincing
    > > points.....
    > >
    > > verses

    ---8<---cutting a bit
    > With all the answers, just think about this : if you properly keep the same
    > saddle to pedal axle distance, then at the top of your pedal stroke, you
    > find your thigh a full centimeter higher, if you switched from 170 to 175.
    > Your initiating muscle groups change, and the timing changes. Your recovery
    > muscle groups work longer, and the timing changes.
    >
    > That said, it's up to you to feel whether these real changes improve or
    > degrade your pedaling. They may not have much effect, also. But if we know
    > that the change of a centimeter in your horizontal extension makes a pretty
    > palpable difference, it may well follow that pedal lengths do influence your
    > performance.
    >
    > Personally, I think they do. Finding which length is your most effectiveor
    > efficient would take a lot of time in each to evaluate. I think Leonard
    > Zinn has done some of that work, but he has his own biases, people say.
    >
    > --
    > Sandy


    I'll share some of my experiences. Original cranks 172,5, inseam length
    85 cm (33,5 in), have had occasional knee problems previously, more
    related to running. Pedalling with seat slightly low, cleats moved back
    towards centre of foot, typical cadence ca. 105.

    Bought 177,5 cranks (C-Rec), lowered seat 5mm, moved it forward 7mm.
    Should've bought a longer stem but didn't bother. Rode 400 km over 3
    weeks, typical cadence appeared to drop to ca. 93. Knees stayed OK,
    since I pedal short gears at highish cadence. But my back muscles (at
    pelvic level) were already fatigued due to overtraining in the period
    before the crank switch. These muscles got worse, probably due to the
    cranks, so I had to switch back to the shorter ones to do one of the
    classic rides here (Sweden, Vättern Rundan, 300 km).

    Now I'm going to spend the summer riding the longer cranks *nice and
    easy*, allowing my back muscles to get used to them. I am also choosing
    a higher saddle position which feels a bit easier when the foot's just
    past the top of the stroke. This change in saddle height addresses
    Sandy's point pretty well I think.

    What I like about the long cranks is that I tend to reduce cadence to a
    more reasonable level without me feeling I'm stressing my joints. My
    hill climbing is so much better too, both sitting and standing. But I
    wouldn't recommend a crank change to everybody; it's a bit of a
    borderline case with me. But I'll try them for 2-3 months more, and
    re-evaluate.

    Sandy, can you pls explain "recovery muscle groups", I'm a novice at
    this.

    BR /Robert
     
  12. Sandy

    Sandy Guest

    colnalu wrote:
    > Sandy wrote:


    > Sandy, can you pls explain "recovery muscle groups", I'm a novice at
    > this.
    >

    I just meant to refer to the muscles which aid in lifting the leg after the
    power part of the stroke, which are also contributory to power production
    when standing.

    --
    Bonne route !

    Sandy
    Vreneuil-sur-Seine FR
     
  13. >If I then dropped
    > the saddle by 18mm, I would then effectively be ~36mm lower, relative
    > to the top half (roughly) of the stroke.
    >
    > I know what would happen if I dropped my saddle right now by 36mm: I'd
    > be a crap rider!!
    >
    > Having said all that, I did give in, and I'm trying 180s, and so far I
    > like them :)
    >
    >
    > --
    > 531Aussie


    The back and top of the stroke are relatively unimportant. The best
    trained cyclists will follow the crank around during this part of the
    cycle, but they aren't really applying a propulsive force. The only
    issue is whether or not you can move your leg that high without causing
    stress in the hamstrings, lower back, knee or elsewhere. During the
    forward part of the stroke where the power is produced, your leg will
    be well extended.

    I actually wish a greater range of crank lengths were available... I'd
    like to try some 150s and 200s just to see how they feel.

    -Ron Ruff
     
  14. > I'll share some of my experiences. Original cranks 172,5, inseam length
    > 85 cm (33,5 in), have had occasional knee problems previously, more
    > related to running. Pedalling with seat slightly low, cleats moved back
    > towards centre of foot, typical cadence ca. 105.
    >
    > Bought 177,5 cranks (C-Rec), lowered seat 5mm, moved it forward 7mm.
    > Should've bought a longer stem but didn't bother. Rode 400 km over 3
    > weeks, typical cadence appeared to drop to ca. 93. Knees stayed OK,
    > since I pedal short gears at highish cadence. But my back muscles (at
    > pelvic level) were already fatigued due to overtraining in the period
    > before the crank switch. These muscles got worse, probably due to the
    > cranks, so I had to switch back to the shorter ones to do one of the
    > classic rides here (Sweden, Vättern Rundan, 300 km).



    Your cranks increased in length by 2.9% but your cadence dropped over 4
    times as much to compensate (12.9%)! At the same power output you would
    need to be applying 10% greater force to the longer cranks. What if you
    had simply lowered your cadence 10% (increasing force 10%) with the
    172.5s? I could be missing something, but it doesn't make sense that
    lowering the cadence by more than the increase in crank length would be
    "optimal", since now you are applying a greater force over a greater
    range to achieve the same result. I would expect greater stress on the
    joints and muscles, or lower power output (slower speed).

    >
    > What I like about the long cranks is that I tend to reduce cadence to a
    > more reasonable level without me feeling I'm stressing my joints. My
    > hill climbing is so much better too, both sitting and standing.


    Did you do a time trial before and after to measure this effect? I'm
    just curious, because it could be that many people who use long cranks
    just like the way they "feel", even though they are going a little
    slower than before... and there is nothing wrong with that unless you
    are racing. Maybe the whole improvement in feel is simply due to riding
    at a slightly reduced pace.

    -Ron Ruff
     
  15. colnalu

    colnalu Guest

    [email protected] wrote:
    > > I'll share some of my experiences. Original cranks 172,5, inseam length
    > > 85 cm (33,5 in), have had occasional knee problems previously, more
    > > related to running. Pedalling with seat slightly low, cleats moved back
    > > towards centre of foot, typical cadence ca. 105.
    > >
    > > Bought 177,5 cranks (C-Rec), lowered seat 5mm, moved it forward 7mm.
    > > Should've bought a longer stem but didn't bother. Rode 400 km over 3
    > > weeks, typical cadence appeared to drop to ca. 93. Knees stayed OK,
    > > since I pedal short gears at highish cadence. But my back muscles (at
    > > pelvic level) were already fatigued due to overtraining in the period
    > > before the crank switch. These muscles got worse, probably due to the
    > > cranks, so I had to switch back to the shorter ones to do one of the
    > > classic rides here (Sweden, Vättern Rundan, 300 km).

    >
    >
    > Your cranks increased in length by 2.9% but your cadence dropped over 4
    > times as much to compensate (12.9%)! At the same power output you would


    I see what you mean but I can't explain it.

    > need to be applying 10% greater force to the longer cranks. What if you
    > had simply lowered your cadence 10% (increasing force 10%) with the
    > 172.5s? I could be missing something, but it doesn't make sense that
    > lowering the cadence by more than the increase in crank length would be
    > "optimal", since now you are applying a greater force over a greater


    I think that I'm deciding my cadence based on how slowly I can rev
    before my muscles/tendons feel strained . On the 172,5's, the
    comfortable pace seems to be at about 105, able to go down to about 92
    before it feels too heavy. On the 177,5's the comfortable pace is
    about 95, able to go to about 85 before the heavy feel. As I get used
    to them, I expect that my cadence will return to roughly the previous
    value or maybe slightly under.

    > range to achieve the same result. I would expect greater stress on the
    > joints and muscles, or lower power output (slower speed).


    Not sure about that idea. My reason for trying the cranks is to see if
    I can, for a given average speed, spread the power delivery over a
    wider range of leg movement. I'm testing the theory that is the
    opposite of yours, that more leg movement will *reduce* muscle stress
    (as far as my joints go, I've already seen from my testing that they
    are faring well, no bad effects).

    >
    > >
    > > What I like about the long cranks is that I tend to reduce cadence to a
    > > more reasonable level without me feeling I'm stressing my joints. My
    > > hill climbing is so much better too, both sitting and standing.

    >
    > Did you do a time trial before and after to measure this effect? I'm
    > just curious, because it could be that many people who use long cranks
    > just like the way they "feel", even though they are going a little
    > slower than before... and there is nothing wrong with that unless you
    > are racing. Maybe the whole improvement in feel is simply due to riding
    > at a slightly reduced pace.


    Good point, but yes I am measuring on same 40 km circuit, and get
    pretty much same average speed.

    I'm also interested in hearing from others who've done - or are doing -
    a similar experiment, who can shed more light on all of this. Is it all
    placebo effect or are there real advantages to be gained here (let's
    ignore for a moment the texts on the Internet from the 3-4 advocates of
    long cranks ...)?

    /Robert
     
  16. >
    > > I would expect greater stress on the
    > > joints and muscles, or lower power output (slower speed).

    >
    > Not sure about that idea. My reason for trying the cranks is to see if
    > I can, for a given average speed, spread the power delivery over a
    > wider range of leg movement. I'm testing the theory that is the
    > opposite of yours, that more leg movement will *reduce* muscle stress
    > (as far as my joints go, I've already seen from my testing that they
    > are faring well, no bad effects).
    >

    Let me try to be more clear. You *would* be reducing the stress if you
    maintained the same cadence as before, for the same power output. Power
    output is proportional to pedal force x crank length x cadence. But
    since you reduced your cadence by a 4+ times greater amount than you
    increased your crank length, you are actually pushing with greater
    average force than before (10% given your numbers), in addition to
    increasing the leg movement by 3%. I wouldn't expect that to feel as
    though you were stressing your joints *less*. That's why I questioned
    whether you were actually producing the same power.
    Do you have a time trial you do regularly on a steep hill? On a rolling
    or flat course the wind could easily swamp out differences that are
    this small. But if you did a steep hill climb (at max effort) on calm
    days, and switched back and forth between the two lengths, you might be
    able to tell something.

    -Ron Ruff
     
  17. colnalu

    colnalu Guest

    [email protected] wrote:
    > >
    > > > I would expect greater stress on the
    > > > joints and muscles, or lower power output (slower speed).

    > >
    > > Not sure about that idea. My reason for trying the cranks is to see if
    > > I can, for a given average speed, spread the power delivery over a
    > > wider range of leg movement. I'm testing the theory that is the
    > > opposite of yours, that more leg movement will *reduce* muscle stress
    > > (as far as my joints go, I've already seen from my testing that they
    > > are faring well, no bad effects).
    > >

    > Let me try to be more clear. You *would* be reducing the stress if you
    > maintained the same cadence as before, for the same power output. Power
    > output is proportional to pedal force x crank length x cadence. But
    > since you reduced your cadence by a 4+ times greater amount than you
    > increased your crank length, you are actually pushing with greater
    > average force than before (10% given your numbers), in addition to
    > increasing the leg movement by 3%. I wouldn't expect that to feel as
    > though you were stressing your joints *less*. That's why I questioned
    > whether you were actually producing the same power.
    > Do you have a time trial you do regularly on a steep hill? On a rolling
    > or flat course the wind could easily swamp out differences that are
    > this small. But if you did a steep hill climb (at max effort) on calm
    > days, and switched back and forth between the two lengths, you might be
    > able to tell something.


    Good point. And given your equation, it should be, for longer cranks,
    possible for me to lower my cadence slightly, put in the same force on
    the pedal, and yet maintain same power output (this is of course not
    taking into consideration a whole heap of hard-to-understand muscle
    contraction/extension related issues due to wider pedalling circle).

    The fact that my cadence has dropped more than expected may well be due
    to my unfamiliarity with the longer cranks. It's possible I'm not
    putting out as much power as before, as you suggest.

    In a parallel sub-thread here, Bob P notes that it takes time to build
    up the cadence after a switch to longer cranks. The best thing for me
    to do would to be to train *easily* for a month and get the legs used
    to the movement. Then do a wind-free circuit of about 20 km (we have
    lots of forest here so that's possible). Redo test with shorter cranks
    one day later, striving for similar average heart rates, and compare
    times.

    /Robert
     
  18. Ron Ruff

    Ron Ruff Guest

    colnalu wrote:

    >
    > BTW does "AT" mean anaerobic threshhold, and do you mean that the
    > larger range of movement may allow me to run a slightly higher pulse
    > (doing more work) before getting hit by the effects of lactic acid
    > build-up? Or will this increased range of movement cause my pulse to
    > run higher for the same power output, causing me to hit the lactic acid
    > thresshold just as quickly, just as the same amount of work (power *
    > time) gets done?
    >
    > /Robert


    Actually... I mean both!... maybe... or maybe not. And yes, AT is
    anaerobic threshold. I'm no physiology expert, but I've been interested
    in this subject and have done some internet research.

    The AT heart rate is not a fixed value at all. It varies depending on
    the type of work being done, and generally when more of the body is
    engaged, the AT heart rate is higher. This makes sense to me, because
    the onset of muscle fatigue will be lessened if the load is spread
    around, even though the heart is beating faster.

    In the case of longer cranks, you're moving through a greater motion,
    which should bring more muscles into play over a greater range, tending
    to increase your AT heart rate. But at the same time it could be less
    *efficient* (higher heart rate for same power), to be working your
    muscles over a greater range, so your heart rate might increase at the
    same power level. So if you see an increase or drop in heart rate at
    max effort, it doesn't necessarily mean anything... you could be
    putting out more power or less.

    Cadence will certainly effect this also. There have been several
    studies done, where researchers concluded that low cadences (around
    50-60 rpm) are most efficient... but efficiency is just a measure of
    energy consumed divided by energy output... in other words they are
    focusing on the condition that burns the fewest calories at a set power
    level...and who cares about that? Cyclists are interested in going
    fast, and higher cadences are necessary to achieve the highest power
    output, even though it is less efficient.

    Regarding heart rate: I set a personal best on a 33 mile course here
    yesterday even though my average heart was 8 bpm lower than "usual"...
    I put that in quotes because I normally see a lot of variation. It was
    windy as usual; I live on Kauai so the wind is pretty consistent... so
    I am fairly sure that I was putting out a little more power to go
    faster. I was a little tired from doing intervals the previous day, and
    that seems to be a correlation... my heart rate is higher if I am fresh
    and lower if I'm tired... at the same power output (speed).

    Anyway, there are lots of variables when we are trying to optimize the
    performance of our bodies on a bike, and I don't think anyone has
    sorted them all out. I certainly wouldn't select heart rate as the
    defining standard because it doesn't correlate with power output very
    well... certainly not for me. A direct power measurement would be the
    best, and if that isn't possible, I think a time trial on a steep hill
    would give the best estimate of your power output.

    You are trying to quantify the changes due to a very small variation,
    also... less than 3% in crank length. This will be very difficult in
    any case... but I wish you well, and be sure to report back with
    whatever you learn.

    -Ron
     
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