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Crank length article in triathlete mag ?
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GregX
Sep 29, 08 10:28
Post #1 of 71 (2138 views)
Crank length article in triathlete mag ?
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i was reading the crank length article in the latest issue (p. 122), it presents some interesting ideas.
but a few things seemed very confusing. for one, there's a quote from John Cobb who says a 6'5'' tall rider he's been working with has "gained 65 watts working down to 165mm cranks." So does that mean that an average height triathlete (say, 5'8'' tall) should be using 140mm cranks to gain some serious watts? (where is Frank Day when you need him?) so where can i get me some 140s? because if i can generate 65 more watts on the bike, i can go pro and start winning some substantial prize money.
then, in the article, Cobb is also quoted as claiming that shorter cranks will allow you to
lower
your seat height. correct me if i'm wrong here, but wouldn't switching to shorter cranks
raise
your seat height (unless you completely re-design your frame) ?
"Half of what we taught you is wrong. Unfortunately, we do not know which half."
-- Dean and cardiologist C. S. Burwell to a Harvard Med School graduating class.
Where would
you
want to swim ?
(This post was
edited
by GregX on Sep 29, 08 11:32)
Andrew Coggan
Sep 29, 08 10:31
Post #2 of 71 (2129 views)
Re: Crank length article in Triathlete mag ? [GregX]
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in the article, Cobb is also quoted as claiming that shorter cranks will allow you to
lower
your seat height. correct me if i'm wrong here, but wouldn't switching to shorter cranks
raise
your seat height
The answer to that question depends upon whether you choose to keep leg extension constant (saddle height must go up) or leg flexion constant (saddle height must go down) when changing crank length.
jaretj
Sep 29, 08 10:41
Post #3 of 71 (2097 views)
Re: Crank length article in Triathlete mag ? [GregX]
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I thought that was interesting too.
As I remember, his rationale was that the rider was allready used to a certain pedal speed and switching to 165's slowed that pedal speed down which made him feel like he was doing less work. Pushing a bigger gear made him feel like he was on a longer crank again. He would therefore have to put out more power to do that.
It appeared to me that it was a PE issue and not a lever/geared advantage issue.
As for being able to lower the seat, his claim was that riders could lower the front end of the bike and not get the leg in the ribs as much with shorter cranks. I agree that you would have to raise the seat a little to keep the same knee angle though.
jaretj
http://jaretj.blogspot.com
Rokko
Sep 29, 08 10:45
Post #4 of 71 (2081 views)
Re: Crank length article in Triathlete mag ? [jaretj]
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I was confused too by the
lowering
the seat comment. I envisioned raising the seat to keep the knee angle the same. I also wasn't too impressed that the article said my cranks are too long, but provided no guideline as to determine what crank length they would actually recommend. I kept reading looking for the meaty detailed part of the article, but the whole thing read like an intro paragraph - just vague details to capture interest.
Just my $0.02
-----
Blazeman Warrior
Wildflower Long, Big Kahuna, maybe Vineman, hopefully Alcatraz
Paulo Sousa
Sep 29, 08 10:45
Post #5 of 71 (2078 views)
Re: Crank length article in Triathlete mag ? [Andrew Coggan]
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In Reply To
In Reply To
in the article, Cobb is also quoted as claiming that shorter cranks will allow you to
lower
your seat height. correct me if i'm wrong here, but wouldn't switching to shorter cranks
raise
your seat height
The answer to that question depends upon whether you choose to keep leg extension constant (saddle height must go up) or leg flexion constant (saddle height must go down) when changing crank length.
Everyone knows that maintaining leg extension is the important factor here...
-
pstriathlon.com
h2ofun
Sep 29, 08 10:45
Post #6 of 71 (2077 views)
Re: Crank length article in Triathlete mag ? [GregX]
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Wow, I have not had a chance to read yet, but, if this is the end results, sure not how I currently feel on the topic.
But, if I, at 6'5", should be using 165's then yes, would a 5'8" need to use 140's?
Bottom line is what ever one is comfortable riding and can get on a new bike is probably what will be used.
Dave
MyAthlete.biz GPS
Bringing families into your racing
GregX
Sep 29, 08 10:47
Post #7 of 71 (2068 views)
Re: Crank length article in Triathlete mag ? [Andrew Coggan]
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The answer to that question depends upon whether you choose to keep leg extension constant (saddle height must go up) or leg flexion constant (saddle height must go down) when changing crank length.
got it. so, if you shorten your cranks by, say, 25mm and you want to maintain the highest possible sustained cycling performance (and you don't re-design your frame), what does good scientific research recommend?
do you lower the saddle or raise the saddle?
"Half of what we taught you is wrong. Unfortunately, we do not know which half."
-- Dean and cardiologist C. S. Burwell to a Harvard Med School graduating class.
Where would
you
want to swim ?
Paul
Sep 29, 08 10:48
Post #8 of 71 (2064 views)
Re: Crank length article in Triathlete mag ? [GregX]
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I did not read the article, but would guess that shorter cranks work better for spinners. Just like how figure skaters spin faster when their arms are closer to the body.
Paul..
Andrew Coggan
Sep 29, 08 11:12
Post #9 of 71 (1993 views)
Re: Crank length article in Triathlete mag ? [GregX]
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if you shorten your cranks by, say, 25mm and you want to maintain the highest possible sustained cycling performance (and you don't re-design your frame), what does good scientific research recommend?
do you lower the saddle or raise the saddle?
I haven't decided yet.
Andrew Coggan
Sep 29, 08 11:13
Post #10 of 71 (1990 views)
Re: Crank length article in Triathlete mag ? [Paulo Sousa]
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In Reply To
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in the article, Cobb is also quoted as claiming that shorter cranks will allow you to
lower
your seat height. correct me if i'm wrong here, but wouldn't switching to shorter cranks
raise
your seat height
The answer to that question depends upon whether you choose to keep leg extension constant (saddle height must go up) or leg flexion constant (saddle height must go down) when changing crank length.
Everyone knows that maintaining leg extension is the important factor here...
A saddle that is too high impacts efficiency/physiology more than one that is equally too low...
GregX
Sep 29, 08 11:19
Post #11 of 71 (1960 views)
Re: Crank length article in Triathlete mag ? [Andrew Coggan]
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has this not been studied?
when martin (and other researchers) change subjects' crank lengths in their studies, don't they generally base seat height on bottom dead center? if yes, what the basis of this choice?
"Half of what we taught you is wrong. Unfortunately, we do not know which half."
-- Dean and cardiologist C. S. Burwell to a Harvard Med School graduating class.
Where would
you
want to swim ?
zipp
Sep 29, 08 11:25
Post #12 of 71 (1945 views)
Re: Crank length article in Triathlete mag ? [GregX]
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We'll see what happens when moving to a shorter crank length in about 45 days. I've been using 180mm cranks for many years on all my bikes. I tried a 195 for a short time but that didn't work real well for me. I just ordered a new bike with proprietary adjustable cranks (look 596), but they only go to 175. So, we'll see what happens when the new bike arrives.
Paul
---------------------------------------------------------
http://casasedona.com
"Don't do stupid shit people" - Tom Demerly
toolguy
Sep 29, 08 11:29
Post #13 of 71 (1935 views)
Re: Crank length article in Triathlete mag ? [GregX]
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Glen Swan a fast rider(and frame builder) from the 90's was in a cycling mag talking about using short cranks,i belive he was a Nat champ age group at one time,Andy might know him he was at the nats in Tallahasse in 98,if i remember he was using 165mm cranks
KarstenKB
Sep 29, 08 12:21
Post #14 of 71 (1864 views)
Re: Crank length article in triathlete mag ? [GregX]
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Haven't read the article, nor do I really care. But thought this experience may be pertinent. I was fit to my bike last year, and one of the things (nearly the only thing) that changed was a shorter crank length. My toe was too pointed at the bottom and knee angle too bent at the top with my old crank length (172.5...I'm 5'9"). Now my ankle and knee angles are better, I'm much more comfortable on the saddle, and my watts saw an immediate improvement. Debate and flame to your heart's content.
________________________________________________
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gabbiev
Sep 29, 08 12:40
Post #15 of 71 (1832 views)
Re: Crank length article in Triathlete mag ? [toolguy]
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I used to race against Glen for many years. He's a relatively short guy--I'd guess 5.5 or 5.6. I know that he was using 167.5's for quite some time. Perhaps he was going fast *despite* the use of short crank arms. I'm only 5.7 and use 175's; Glen and I pretty much rode almost identical times. Perhaps I would have gone faster if I was on *shorter* cranks.
Personally, I don't believe that a few mm's in crank length makes all that much difference, nothwithstanding anomolous cranks, such as 200mm or 140's....
John Cobb
Sep 29, 08 15:43
Post #16 of 71 (1726 views)
Re: Crank length article in Triathlete mag ? [jaretj]
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I know that the article said "lower the seat height" but what I meant was lower the whole seat in relation to the ground. I have found that you have to raise the saddle height with the shorter cranks. I was suggesting building new frames with different geometry for this.
New Blog - www.johncobbresearch.com
GregX
Sep 29, 08 16:16
Post #17 of 71 (1681 views)
Re: Crank length article in Triathlete mag ? [John Cobb]
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John, thanks for the response. i guess the writer mis-quoted you on that.
but regarding the other thing, can an average-height rider gain 65 watts by going to 140mm cranks (like your taller rider)?
"Half of what we taught you is wrong. Unfortunately, we do not know which half."
-- Dean and cardiologist C. S. Burwell to a Harvard Med School graduating class.
Where would
you
want to swim ?
Frank Day
Sep 29, 08 16:37
Post #18 of 71 (1648 views)
Re: Crank length article in triathlete mag ? [GregX]
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]
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i was reading the crank length article in the latest issue (p. 122), it presents some interesting ideas.
but a few things seemed very confusing. for one, there's a quote from John Cobb who says a 6'5'' tall rider he's been working with has "gained 65 watts working down to 165mm cranks." So does that mean that an average height triathlete (say, 5'8'' tall) should be using 140mm cranks to gain some serious watts? (where is Frank Day when you need him?) so where can i get me some 140s? because if i can generate 65 more watts on the bike, i can go pro and start winning some substantial prize money.
then, in the article, Cobb is also quoted as claiming that shorter cranks will allow you to
lower
your seat height. correct me if i'm wrong here, but wouldn't switching to shorter cranks
raise
your seat height (unless you completely re-design your frame) ?
It is not possible to actually know what changing crank length can do or has the potential to do for each individual athlete without that athlete actually trying (and training with) the various options and seeing what happens. I can make a strong "theoretical" argument for and against both longer and shorter crank lengths. It is one reason that we offer the adjustable crank length option.
Frank (can't be a scientist because I am a physician) Day
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be sure you are signed up for our newsletter. Sign-up at
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(This post was
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by Frank Day on Sep 29, 08 16:39)
John Cobb
Sep 29, 08 17:05
Post #19 of 71 (1616 views)
Re: Crank length article in Triathlete mag ? [GregX]
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I really don't know about that, my adjustable cranks only go down to 165. I suspect that there might be some gains for shorter riders but but just guessing, I think 140 might be kinda' short. I suspect there is some type of data curve that would show the power changes flatten out once your down to a certain crank length. Something to do with muscle firing times vs time required for power. Some of the smart guy's on here would know more about this than me. I do think that a realistic gain of 30 - 50 usable watts can happen for most riders but you have to work with the gear ratios and run bigger gear inches than what most would consider normal.
New Blog - www.johncobbresearch.com
devashish_paul
Sep 29, 08 17:21
Post #20 of 71 (1593 views)
Re: Crank length article in Triathlete mag ? [John Cobb]
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How does foot size factor in? Take 2 guys one with size 7 the other with size 14 feet? Would it be tough for the person with flipper feet to pedal on 140mm cranks vs the person with smaller feet?
EDIT: My gut feel is that you don't want the crank length to get much smaller than distance from heel to ball of foot, or you'd have difficulty pushing down effectively on the downstroke.
(This post was
edited
by devashish_paul on Sep 29, 08 17:40)
h2ofun
Sep 29, 08 17:26
Post #21 of 71 (1588 views)
Re: Crank length article in Triathlete mag ? [John Cobb]
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John, how many tall folks have you talked with and or tested? I know, at 6'5", I love my 200mm cranks and find them a real help for me climbing. Every tall person I have talked to that is using longer cranks would never go back either. Oh well, this is one of those topics that will never be agreed as to what the right answer is, but I am staying with my longer cranks.
Dave
MyAthlete.biz GPS
Bringing families into your racing
rayhuang
Sep 29, 08 17:31
Post #22 of 71 (1583 views)
Re: Crank length article in Triathlete mag ? [John Cobb]
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Lets say I am in need of testing this myself and am willing to devote the trainer time (with a Powertap) and possibly a Computrainer to finding my ideal crank length and thus dial in a powerful aerodynamic position? What is the protocol to figure the crank length portion out?
My problem right now is my very upper thighs hit my body with 172.5 cranks. But I am pretty sure the cranks are too long for me judging by the time it took for me to try and adapt to them and bring up my cadence back from low 80's back to low 90's since switching from 170's to 172.5's. Other factors played a part like going to a UCI legal position and not sitting on the nose of the saddle.
Understand I am a fairly new cyclist (who quit 14+ years and came back fall 2006) so everything is changing, but I want to dial in what I can.
I read recently that Andy Coggan uses 165's on one of his TT bikes and since he is about my height (5"9") and inseam (31")it really got me thnking. Especially since my thighs hit my body (or more accurately fold into my abdomen at the top of ths stroke). Its a limiter to lowering the bars, which I feel I have the flexibility to do now.
Of course I possibly have the option of raising the saddle and sitting on the nose and then lowering the bars a smidge more.
Understand windtunnel time is out of the question this cming year. I dont have the budget.
TIA,
Ray
... ... ... ... ...
http://www.raysracingadventures.blogspot.com
garageman
Sep 29, 08 17:44
Post #23 of 71 (1159 views)
Re: Crank length article in triathlete mag ? [Frank Day]
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I would love to try shorter cranks, the best product on the market to experiment seems to be Franks adjustable PC's.. If they were cheaper (like half the price) I would give them a go.
h2ofun
Sep 29, 08 18:05
Post #24 of 71 (1152 views)
Re: Crank length article in triathlete mag ? [garageman]
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Here is another option.
http://www.hscycle.com/...ustablecrankset.html
Dave
MyAthlete.biz GPS
Bringing families into your racing
Andrew Coggan
Sep 29, 08 18:07
Post #25 of 71 (1148 views)
Re: Crank length article in Triathlete mag ? [rayhuang]
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I read recently that Andy Coggan uses 165's on one of his TT bikes and since he is about my height (5"9")
You must have me confused with someone else: I'm 6'0".
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