Please explain crank length theory?
greg
never realized it until now, but according to all the measurement
theory, I should be using a 168.5 or 170 mm crank. I really don't
understand the logic behind this as the 175 mm feels fine. But then, I
really don't know anything different on my bike. Also, according to
basic lever action physics, would there not be a power advantage using a
slightly longer crank? My wife has a 168.5 crank on her bike. When I've
been on it, it feels like I'm spinning too much. Can this not be
modified by gear ratios? What is the reasoning behind this theoretical
crank length sizing and how important is it?
GARTH LIBRE
fit a man 5'9" (54cm to 56 cm) on a road bike. My understanding was that the
two crank sizes recommended for a man of your size would be a low of 170 and
a high of 172.5 or 175. Now what measurement theory have you read that
specifies 170 mm? It does seem to be a lot by preference but the difference
between a crank of 170 and one of 175 is less than 1/4 of an inch. Does this
sound like an earth shattering difference? My thought is that many pros of
your size have chosen both the 170 and the 175. A lot has to do with fashion
as in the old days the 170 was prefered and now the prefered is 172.5. Your
book has you at 168.5 and 170. Between all the opinions that gives us every
conceivable option. Who are you going to believe? I don't know myself, I am
willing to hear from others that have experimented and so know better. Garth
greg <gr...@on.aibn.com> wrote in message
news:3BAABAF8...@on.aibn.com...
Sheldon Brown
I'm working on an article on this topic. At present it's only in a
preliminary draft stage, but you still might find it informative. Here goes:
Different cyclists have different leg lengths. It
seems obvious that crank length should be
proportional, so long legged cyclists should have
long cranks, short-legged cyclists should have short
cranks....and yet, 99.9% of adult bicycles have
crank lengths between 165 and 175 mm. Have the
bicycle manufacturers joined in a great conspiracy
to force everybody to ride the same length cranks,
regardless of their needs?
This is a common misunderstanding. The "leverage"
of a bicycle drive train, also known as "gain
ratio" depends on the crank length, wheel diameter
and the sizes of both sprockets.
Yes, if you go to longer cranks without changing any
of the other variables, you will have more
"leverage", which is another way of saying you'll
have a lower effective gear...but on a multi-speed
bike, you can change gears at will.
With 175, my knees come up too much, causing me knee
problems.
Ay, there's the rub! Assuming you adjust your
gearing appropriately, crank length has no effect on
leverage, it just has to do with the range of motion
of the knee joint.
Too long cranks cause excessive knee flex, and can
cause pain/injury if it causes your knee to flex
more than it is used to.
On the other hand, there doesn't seem to be any
deleterious effect from shorter cranks.
I've been experimenting with this a bit myself
lately. I commonly ride 165 mm cranks with a 42/15
ratio on 700c or 27 inch wheels, when I'm riding
fixed. This gives a gain ratio of 5.8.
On multi-speed bikes I usually ride 170s. I'm 6
feet tall with long legs and a short upper body. I
tried 180s for a while, they came on a used bike I
bought. They made my knees hurt every time I rode
that bike.
My latest experiment is taking place on plastic
Trek frame I picked up in a barter deal. I had a
pair of TA 150 cranks that used to be on my kids'
Cinelli BMX bike, so I've put these on the Trek.
I'm running a 45/17, which gives a gain ratio of
5.9, just a bit higher.
When I first get on the bike after riding with
longer cranks, it feels a bit funny at first, but
within a very short distance it's just fine. I go
just as fast, climb just as well. For a given
speed, my pedal rpm is higher (though my pedal
_speed_ is the same) but the short cranks make it
easy to spin much faster than I normally would.
After riding this bike for a few miles, when I get
back on "normal" cranks, they feel a bit weird and
long at first, then I get used to them after riding
a couple of minutes.
I think people really obsess too much about crank
length. After all, we all use the same staircases,
whether we have long or short legs. Short legged
people acclimate their knees to a greater angle of
flex to climb stairways, and can also handle
proportionally longer cranks than taller people
normally use.
Those unfamiliar with the gain ratio concept can
read about it at http://sheldonbrown.com/gain.html
Sheldon "Crank Posting" Brown
+-------------------------------------------------+
| To stay young requires unceasing cultivation |
| of the ability to unlearn old falsehoods. |
| --Robert A. Heinlein |
+-------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772, 617-244-1040 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
Neal L. Grotenstein
Crank arm length is still art and science. Shortly before joining the
Polish National Team, former US Coach Eddie B. had chosen that as a
dissertation topic.
The numbers used 10+ years ago had road bikes in mind. Still good.
--The theoretical ATB environment of rocks and mud improves with longer
crank arms,more leverage. Great for the best 1% of us.
--The real world of ATB use is paved roads and neighborhood trails, where
the other 99% of us are better off with road use oriented crank
arm lengths.
--Personal note: I'm 5'7" and buy pants with leg lengths of 29 or 30"
I ride 170mm. For 2 weeks I borrowed a 171 mm crankset. Noticeable
difference - it just felt too big. I happily returned to 170mm.
I've learned from fooling arouind with crank length, bar width,
and stem length that the body doesn't fully follow algebra
rules. Everyone posting here is good at math, so it gets over valued.
Everyone here is ungood at grammar, spelling, and social graces,
so they are undervalued here. Somewhere in between...
This really must be seen in a marketing context, not physiology.
"Product differentiation" calls for sufficient difference between
similar products for customers to want to buy one of each, such as
road and ATB bikes, or a Palmtop and desktop PC. Marketing
101 stresses things like that.
I've concluded that every time technical reasons don't explain
something in the business world, factor in marketing. Bikes resembling
racing bikes sell better than plain vanilla ones.
The US economy is not so hot, so you have customer leverage. Use that
to get a bike set up for _you_ and the way it'll be used.
Neal Grotenstein
ne...@cpcug.org
www.cpcug.org/user/nealg/
Roger Marquis
>I'm 5'9"(176 cm) with an inseam of 31"(79 cm). I use a 175 mm crank. I
>never realized it until now, but according to all the measurement
>theory, I should be using a 168.5 or 170 mm crank. I really don't
>understand the logic behind this as the 175 mm feels fine. But then, I
>really don't know anything different on my bike.
See http://www.roble.net/marquis/crank.length
--
Roger Marquis
http://www.roble.net/marquis/
Varuna Jyothi
can notice the effect of 2.5mm difference in crank length in terms of how
easy it is to spin smoothly. With a 32" inseam I find 170s work well and
(besides increased knee soreness) 172.5s or 175s won't spin as fluidly for
me. I even use 170s on my mountain bike. For me crank length is one of the
more important aspects of fit, right up there with seat height.
greg <gr...@on.aibn.com> wrote in message
news:3BAABAF8...@on.aibn.com...
Bob VonMoss
> I have knee problems and can notice when cranks are too long for me. I also
> can notice the effect of 2.5mm difference in crank length in terms of how
> easy it is to spin smoothly. With a 32" inseam I find 170s work well and
> (besides increased knee soreness) 172.5s or 175s won't spin as fluidly for
> me. I even use 170s on my mountain bike. For me crank length is one of the
> more important aspects of fit, right up there with seat height.
comments on my experience:
- I am 6'1", 31" inseam, long torso
- by most of those charts I should be using 170 mm cranks.
- 20 years ago I raced BMX and 175 was standard for 1 piece cranks and I used
that length for about 3 years. I experimented back then with the 7 1/2"
(192.5mm) Ashtabula, which some pros used, but quickly gave up on them and just
could not go faster. A lot of people in BMX used 180 cranks. I never felt I
needed something longer than 175 in BMX. People with "alloy" 3 piece cranks
typically had 170 cranks. I never had a bike with these on for any length of
time. I could ride the bike, but disliked them.
- years later in 1997 I got a hybrid with 170 cranks. I think at first I was not
aware what length they were. They were OK, but later when I migrated to another
bike, I just went to 175. Since I ride only in an urban environment (Chicago
city streets), I noticed dramatic improvement when taking off from red lights,
but then who really cares.
- since 1998 I just stuck with 175. I feel like I have my rythym on 175's and am
able to spin lower gears 80-100 rpm fairly easily. The only time I had knee
problems was when I rode someone else's bike when the seat was too low (that
bike had 170, though not at fault), or cleats were not aligned. I guess I'm not
old enough to get knee problems.
- I think if I was in a situation where I was riding for miles without stopping
or climbing or rapid starts, then 170 or 172.5 might be better. People don't
usually mention much that the shorter cranks have less to travel, so spinning is
possibly less arduous on the legs. I guess we always think bigger is better. I
have to admit that my initial impression when I step over a bike with 170 cranks
is they suck--I feel robbed of power. Like others are saying, it's really not a
big deal. You gain a little in one department, but trade off something else. In
some ways things balance out. If you're not racing, it's really not a big deal.
I happened to get a second bike with 172.5 cranks, so I suspect at some point
I'll be doing more evaluation in the future on 172.5's for urban use.
and...@thankstomycranks.com
--
Andrew Bradley
www.thankstomycranks.com
and...@thankstomycranks.com
ordinaries (high-wheelers)?
Seems to me that by the gain argument, they didn't need a high wheel at
all, just short cranks.
--
Andrew Bradley
www.thankstomycranks.com
Sheldon Brown <Capt...@sheldonbrown.com> wrote in message
news:3BAABAAD...@sheldonbrown.com...
Bill Robertson
news:3BAABAAD...@sheldonbrown.com...
> I think people really obsess too much about crank
> length. After all, we all use the same staircases,
> whether we have long or short legs. Short legged
> people acclimate their knees to a greater angle of
> flex to climb stairways, and can also handle
> proportionally longer cranks than taller people
> normally use.
I'm not sure the climbing stairs analogy holds up. After all, people don't
generally spend any more than a couple of minutes per day climbing stairs,
and they certainly don't go on a two week stair-climbing holiday or put in
a hard one-hour stair-climbing session several times a week. Do they?
- Bill -
Bill Robertson bi...@plumtree.org.uk
--
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via Mailgate.ORG Server - http://www.Mailgate.ORG
Zilla
"Neal L. Grotenstein" <ne...@cpcug.org> wrote in message
news:Pine.GSO.3.96.101092...@cpcug.org...
> --Personal note: I'm 5'7" and buy pants with leg lengths of 29 or 30"
> I ride 170mm. For 2 weeks I borrowed a 171 mm crankset. Noticeable
> difference - it just felt too big. I happily returned to 170mm.
You "felt" the 1mm difference? That's about the thickness of a paper
clip. Wow!
Zilla
John Forrest Tomlinson
news:x7Fq7.365716$TM5.55...@typhoon.southeast.rr.com...
I can certainly feel a couple millimeters. Not in the size of the
circle my feet go through, but at the top of the pedal stroke.
JT
--
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Sheldon Brown
>
> Historians out there, what length of crank did they use on the old
> ordinaries (high-wheelers)?
>
> Seems to me that by the gain argument, they didn't need a high wheel at
> all, just short cranks.
High wheelers (they haven't been "ordinary" for over a century) used
adjustable cranks, this being the only way available to vary the gain
ratio on an individual bike. They tended to use shorter cranks than
modern bikes.
The limiting factor with a high wheeler was the rider's leg length,
which limited how large a wheel he could straddle and reach the pedals.
As a practical matter, all high wheelers had lower-than-ideal gain
ratios, and high wheeler racing was definitely a tall man's game.
Sheldon "Not Quite That Old" Brown
+-------------------------------------------------------+
| Military conscription is the worst form of slavery. |
| A more enlightened age will consider it a War crime. |
+-------------------------------------------------------+
Mark M
news:Pine.GSO.3.96.101092...@cpcug.org...
> I've learned from fooling arouind with crank length, bar width,
> and stem length that the body doesn't fully follow algebra
> rules. Everyone posting here is good at math, so it gets over valued.
Wrong. Not possible overvalue math. Specially correct math.
> Everyone here is ungood at grammar, spelling, and social graces,
Who you say bad at grammar? We no got puur shpurlink.
If you say we socially not graceful, we say you stupid bastard.
> so they are undervalued here. Somewhere in between...
None of those are undervalued, they are all too rare everywhere. But you
make a mistake if you arrogate their judgement to yourself.
Mark M
Chris Reeder
>
> Andrew Bradey asked:
> >
> > Historians out there, what length of crank did they use on the old
> > ordinaries (high-wheelers)?
> >
> > Seems to me that by the gain argument, they didn't need a high wheel at
> > all, just short cranks.
>
> High wheelers (they haven't been "ordinary" for over a century) used
> adjustable cranks, this being the only way available to vary the gain
> ratio on an individual bike. They tended to use shorter cranks than
> modern bikes.
Just like commuter UNIcycles these days, which use a large diameter tire
(Coker Tire company makes a pneumatic 36x2.25 which works great). On
flat ground, you can get away with 4-5 inch cranks for some decent
cruising speeds ~12-15mph. But if you ride in hilly country, you end up
liking 6 inch cranks better.
Chris Reeder
and...@thankstomycranks.com
Sheldon Bown wrote:
> Andrew Bradey asked:
> >
> > Historians out there, what length of crank did they use on the old
> > ordinaries (high-wheelers)?
> >
> > Seems to me that by the gain argument, they didn't need a high wheel at
> > all, just short cranks.
>
> High wheelers (they haven't been "ordinary" for over a century) used
> adjustable cranks, this being the only way available to vary the gain
> ratio on an individual bike. They tended to use shorter cranks than
> modern bikes.
>
> The limiting factor with a high wheeler was the rider's leg length,
> which limited how large a wheel he could straddle and reach the pedals.
>
> As a practical matter, all high wheelers had lower-than-ideal gain
> ratios, and high wheeler racing was definitely a tall man's game.
Good info Sheldon, with interesting crank-length implications.
--
Andrew Bradley
www.thankstomycranks.com
Dave Blake
It is almost irrelevant.
There have been several studies of the effects of crank length
on output, and none of them have given any substantial evidence
to suggest that you should change for any mechanical or
physiological rationale.
OTOH, if it feels better, stick with it.
I have 180 mm cranks on my MTB, and the only thing I got when
switching to them instead of 175s was less wheel clearance over
logs.
--
Dave Blake
dbl...@phy.ucsf.edu
Bluto
> I ride 170mm. For 2 weeks I borrowed a 171 mm crankset. Noticeable
> difference - it just felt too big. I happily returned to 170mm.
I smell cattle here. I'd guess that in a blind test you wouldn't even
know which one you were turning unless the Q-factor was seriously
different.
I am a machinist, accustomed to measuring, sizing, and estimating
sizes with all the precision I can manage, and if I can't tell a 1mm
difference in length between two cranks without laying them in contact
with each other (and I can't), then your legs would have to be made by
Browne & Sharpe to tell the difference.
I have used lots of crank lengths between 170 and 195mm, and I can
_sorta, kinda_ tell a 5mm change-- but I wouldn't lay money on it. A
10mm change is easy to feel.
I think that blind tests with a 172.5 and 175 crank would expose a lot
of folks who claim to feel miniscule variations in crank length as
deluded. Unfortunately their delusions give manufacturers a ready
excuse to make 3 basically identical crank lengths to serve all
riders. I say if legs vary in length by 25% (for example), then so
should cranks.
> I've learned from fooling arouind with crank length, bar width,
> and stem length that the body doesn't fully follow algebra
> rules.
If you think so, it's because you have not had an opportunity to try
different body parts for different results to your equations. Or
because you failed to identify all the variables. Or because algebra
doesn't suit you.
> I've concluded that every time technical reasons don't explain
> something in the business world, factor in marketing.
Agreed. But when your market believes it's got micrometers for legs,
that screws things all up.
Chalo Colina
David L. Johnson
> I ride 170mm. For 2 weeks I borrowed a 171 mm crankset. Noticeable
> difference - it just felt too big. I happily returned to 170mm.
If you can tell any difference between 170mm and 171mm, then you really need
to make sure there are no peas under your bottom mattress. Most people could
barely tell any difference between 170 and 172.5 (the next common size, BTW).
There would be a noticable difference between 170 and 175 or 165 -- but it is
not really a problem. Most of us rode track bikes with cranks 5mm shorter
than our road bikes, and could manage the shift easily. Only when you get
10mm over your accustomed size would most of us be annoyed or feel we were
flailing around too much.
--
David L. Johnson
__o | "What am I on? I'm on my bike, six hours a day, busting my ass.
_`\(,_ | What are you on?" --Lance Armstrong
(_)/ (_) |
Phil Holman
> >
> > I'm 5'9"(176 cm) with an inseam of 31"(79 cm). I use a 175 mm crank. I
> > never realized it until now, but according to all the measurement
> > theory, I should be using a 168.5 or 170 mm crank. I really don't
> > understand the logic behind this as the 175 mm feels fine. But then, I
> > really don't know anything different on my bike. Also, according to
> > basic lever action physics, would there not be a power advantage using a
> > slightly longer crank? My wife has a 168.5 crank on her bike. When I've
> > been on it, it feels like I'm spinning too much. Can this not be
> > modified by gear ratios? What is the reasoning behind this theoretical
> > crank length sizing and how important is it?
>
> I'm working on an article on this topic. At present it's only in a
> preliminary draft stage, but you still might find it informative. Here goes:
What I read was OK. How about the racing spin (metaphorically speaking).
Phil Holman
Bluto
> On the other hand, there doesn't seem to be any
> deleterious effect from shorter cranks.
I think that the tradeoff comes in lower performance and higher
effort. As an example, I propose an evaluation of the concerns of two
different riders. I'll call them Little Man and Big Man. Little Man
is 64" tall. Big Man is proportioned identically, but he is 80"
tall-- a 5:4 ratio.
Little Man weighs 140 lbs. Because volume increases as the cube of
the ratio, Big Man weighs 275 lbs.
Little Man is not stupid about crank length-- he uses 165mm cranks,
and has no problems. He likes a 45/18 gear on his bike, gain ratio
5.1:1. When he applies 50 lbs. of force at the pedals, he is pushed
along by a thrust equivalent to 7.0% of his body weight.
Big Man figures that Little Man's setup is good, that the gain is what
matters, right? But to get the same 7.0% thrust/weight ratio, he has
to push on the pedal with a 98 lb. force. No big deal, he's bigger,
right? But...the cross section of his leg-- the cartilage surface of
his knee, for instance-- has only increased by the square of the
ratio. So he's actually loading his knee tissue and tensioning his
leg muscle 25% more per unit area than Little Man, to get the same
performance!
The only other thing Big Man can summon more of to even the scales
with Little Man, output-wise, is length of stroke. He's got more of
it. So he gets a mad genius to machine up some 206mm cranks, 1.25
times as long as Little Man's. Suddenly his gain drops to 4.08:1.
But because the gain is lower, he only has to push 80% as hard, 78
lbs., to get the 7.0% thrust to weight ratio that was taking 98 lbs.
of force before. He has brought his knee loading and muscle tension
to the same as Little Man's, per unit area, and he isn't having to
bend his knee to any tighter an angle than the little guy is. Bless
that mad genius!
It's not quite as simple as that, of course. Big Man has legs that
weighs twice as much as Little Man's, and he's not going to want to
reciprocate them quite as fast as his small companion. But the
balance between gear and cadence is his to find, and it will be easier
for him to manage it with his nifty new 206mm cranks.
The sorry part is, it took him a mad genius to get him his cranks.
His LBS couldn't help him. They just said, "use 175s. Or we can
special order 180s. Gotta watch out for your knees, though." Were
they really watching out for the man's knees? Or just condemning him
to be slower than necessary?
> I think people really obsess too much about crank
> length. After all, we all use the same staircases,
> whether we have long or short legs.
If there were athletic competitions that involved running up
staircases, I believe that there would be a correlation between the
top performers' predominant body size and the proportion of the
stairs.
Chalo Colina
Tim McNamara
four with 175 mm cranks. I can't tell 'em apart.
IMHO this is the kind of crap that gets in the way of riding bikes.
Put your feet in the pedals, ride the bike. These miniscule
differences are like angels dancing on the head of a pin.
Philip
Can you imagine it? Knicker-clad gents with in shirtsleeves hurtling along a
grass track at breakneck speeds (literally) of about 15 miles per hour on
huge wheels while ladies cheered to bust a gusset.
Wow.
I'd do that.
-Philip
Sheldon Brown wrote in message <3BAB4D71...@sheldonbrown.com>...
>Andrew Bradey asked:
and...@thankstomycranks.com
Bluto <chump...@hotmail.com> wrote in message
news:8b4b7de4.01092...@posting.google.com...
>
> If there were athletic competitions that involved running up
> staircases, I believe that there would be a correlation between the
> top performers' predominant body size and the proportion of the
> stairs.
There probably would, but it wouldn't be the same as for crank-length since
body-weight and strength-to-weight are huge factors on the stairs but not on
the bike.
(OTBE large people have lower strength-to-weight.)
You can observe tall Ethiopian type runners taking shorter strides than
shorter rivals, it's all about weight, muscle cross-section and
lever-length.
Proportionality of "stride" is not a sound theory for most activities.
--
Andrew Bradley
www.thankstomycranks.com
Sheldon Brown
>
> > On the other hand, there doesn't seem to be any
> > deleterious effect from shorter cranks.
Chalo Colina responded thoughtfully:
> I think that the tradeoff comes in lower performance and higher
> effort. As an example, I propose an evaluation of the concerns of two
> different riders. I'll call them Little Man and Big Man. Little Man
> is 64" tall. Big Man is proportioned identically, but he is 80"
> tall-- a 5:4 ratio.
>
> Little Man weighs 140 lbs. Because volume increases as the cube of
> the ratio, Big Man weighs 275 lbs.
>
> Little Man is not stupid about crank length-- he uses 165mm cranks,
> and has no problems. He likes a 45/18 gear on his bike, gain ratio
> 5.1:1. When he applies 50 lbs. of force at the pedals, he is pushed
> along by a thrust equivalent to 7.0% of his body weight.
>
> Big Man figures that Little Man's setup is good, that the gain is what
> matters, right? But to get the same 7.0% thrust/weight ratio, he has
> to push on the pedal with a 98 lb. force. No big deal, he's bigger,
> right? But...the cross section of his leg-- the cartilage surface of
> his knee, for instance-- has only increased by the square of the
> ratio. So he's actually loading his knee tissue and tensioning his
> leg muscle 25% more per unit area than Little Man, to get the same
> performance!
>
> The only other thing Big Man can summon more of to even the scales
> with Little Man, output-wise, is length of stroke...
Nope, see below.
> ...He's got more of
> it. So he gets a mad genius to machine up some 206mm cranks, 1.25
> times as long as Little Man's. Suddenly his gain drops to 4.08:1.
> But because the gain is lower, he only has to push 80% as hard, 78
> lbs., to get the 7.0% thrust to weight ratio that was taking 98 lbs.
> of force before. He has brought his knee loading and muscle tension
> to the same as Little Man's, per unit area, and he isn't having to
> bend his knee to any tighter an angle than the little guy is. Bless
> that mad genius!
This is a nice analysis, but misses the point. I never asserted that
Little Man and Big Man need the same gain ratio, and you make a very
plausible case that they don't.
My point is that either of them can obtain any desired gain ratio
without varying the crank length, by selecting different gears. If Big
Man were to shift to a 36 tooth chainring, or to a 22.5 tooth rear
sprocket (those are even harder to find than 206 mm cranks,
unfortunately) he'd get the same 4.1 gain ratio without changing crank
length.
Sheldon "Not Convinced" Brown
+------------------------------------------------+
| According to the latest official figures, |
| 43% of all statistics are totally worthless. |
+------------------------------------------------+
Jim Martin
Hello All:
Let me congratulate all of you for the rigorous way in which you have
approached the issue of determining optimal crank length. This was an issue
of great interest for me when I started my graduate training. At that time I
was coaching two match sprinters: one was 6'6" and the other was 5'8" with
proportionally short legs. Both were using 165mm cranks and it just didn't
seem possible that a single length was optimal for both of them. I felt that
the taller rider should use longer cranks and the shorter rider should use
shorter cranks... but then.... what about pedaling rate and gear ratios?
In the time since then, I have conducted 4 studies on crank length: 3 have
to do with maximal power and 1 is a study of submaximal metabolic cost (i.e.
cycling efficiency). The results of the first two studies
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=10828327&dopt=Abstract
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=11417428&dopt=Abstract
demonstrated that crank lengths of 145 to 195mm do not significantly alter
maximal power. The more interesting finding is the way in which crank
length, pedaling rate, and pedal speed are related and how the optimal speed
changes with crank length..... I'll let the interested reader go and read
the manuscripts.
In a third study, which will be published in European Journal of Applied
Physiology next spring, we reported that the maximal power of 8-11 year old
children is not compromised when they use 170mm cranks. The final study
which is currently in review determined that crank length did not affect the
metabolic cost of submaximal cycling. Interestingly, the effects of crank
length, pedaling rate and pedal speed is different than that for maximal
power. I will post links to the abstracts for those papers when they become
available. I believe that you may find the details of these studies
interesting from the perspective of both basic and applied science and that
they will answer many of the theoretical questions posed in this thread.
Cheers,
Jim
Peter Cole
> _sorta, kinda_ tell a 5mm change-- but I wouldn't lay money on it. A
> 10mm change is easy to feel.
>
What has been your experience in trying all these cranks? What do you use?
Peter Cole
"R. Himm" <no...@none.none> wrote in message
news:none-ya02358000...@news.globetrotter.net...
>
> One could easily think they do, as someone else here explains on their
> website: take a photo of a small man on short cranks, and scale it up, to
> suggest that a large man should use large cranks to experience the same
> results. But as noted, a large man is not a scaled up small man; the
> proportions do not remain the same, just as an adult is not a scaled up
> baby.
Actually, as near as I can tell, a large man *is* a scaled up small man. I'm
6'10", and all my proportions are uniformly larger. I have been told that my
internal organs are larger, and have had problems with some medical & dental
procedures because of being outside the range that the instruments could
handle.
Not all things on bikes are built to scale, and I'm often curious as to why.
Certainly many components could be custom made "to scale", but I'm not sure
of the advantage, if any. Not only are cranks not commonly sized
proportionally, but neither are many frame dimensions, like toptube or
wheelbase lengths.
Jim Martin
The results of our investigations demonstrated that crank length does not
affect maximal power or submaximal efficiency. Consequently, a cyclist may
choose any crank length he or she prefers without concern that the length
will compromise performance. The flip side is that, unfortunately, no
"optimized" crank length will act as a magic performance enhancer.
Cheers,
Jim
Trevor Jeffrey
<Capt...@sheldonbrown.com> writes:
>On the other hand, there doesn't seem to be any
> deleterious effect from shorter cranks.
Leg muscles acting through a narrow range of movement do not function as well
in getting rid of the waste product. Large movement also protect the joints
allowing synovial fluid to lubricate parts which otherwise would be 'running
dry'.
I believe thigh length is proportional to crank length in the ratio of 8:3
This gives the rider just enough clearance in the full tuck position. Obesity
is an axception.
--
Trevor M Jeffrey
Who is not re-inventing the wheel.
Eat your greens before email.
------
and...@thankstomycranks.com
Jim Martin <jma...@xmission.com> wrote in message
news:9oiukk$27c$1...@news.xmission.com...
> One last point:
>
> The results of our investigations demonstrated that crank length does not
> affect maximal power or submaximal efficiency.
Wait on, Jim, last time you suggested that the tall and short would loose
less than 0.5% of their max power if forced to use a 170 crank.
Vague but possibly significant.
Certainly 0.5% could easily be enough to win a championship.
I shall have to get hold of those papers.
>Consequently, a cyclist may
> choose any crank length he or she prefers without concern that the length
> will compromise performance. The flip side is that, unfortunately, no
> "optimized" crank length will act as a magic performance enhancer.
I have a different conclusion, for the racer at least. Most of us should be
on shorter cranks to make the tuck as easy as possible.
Certainly the short among us stand to gain quite a lot.
But crank-length isn't yet finished, Jim. Don't retire yet. How about the
effects of crank-length on endurance and injury.
--
Andrew Bradley
www.thankstomycranks.com
Jim Martin
<and...@thankstomycranks.com> wrote in message
news:Qiqr7.878$1t.92421@stones...
> Wait on, Jim, last time you suggested that the tall and short would loose
> less than 0.5% of their max power if forced to use a 170 crank.
Very astute. In the regression analysis we used in the EuroJAP paper we
determined that the maximal power of our tallest (6'6") and shortest (5'4")
rider would only be compromised by less than one half of one percent (~6
watts out of 1200 watts).
> I have a different conclusion, for the racer at least. Most of us should
be
> on shorter cranks to make the tuck as easy as possible.
Again, very astute. Because crank length has little or no affect on power,
you can choose a crank based on other considerations such as aerodynamic
drag. I personally use 165's on my TT bike for that reason.
> But crank-length isn't yet finished, Jim. Don't retire yet. How about the
> effects of crank-length on endurance and injury.
The paper on submaximal metabolic cost (i.e. endurance performance power) is
in review right now and should be out sometime next year. The results
indicate no significant effect of crank length so, again, pick any length
you like.
Cheers,
Jim
Andrew Coggan
Andy Coggan
Phil Holman
> The paper on submaximal metabolic cost (i.e. endurance performance power) is
> in review right now and should be out sometime next year. The results
> indicate no significant effect of crank length so, again, pick any length
> you like.
What about cadence and submaximal power. Lots out there that use
longer cranks to grind a bigger gear at a lower cadence????
Phil Holman
Jim Martin
"Phil Holman" <phi...@earthlink.net> wrote in message
news:7a4a1cb1.01092...@posting.google.com...
Hi Phil:
That's a good point. Our results indicated that the main predictor of submax
cost (i.e. the metabolic cost of producing power) was the speed at which the
pedal traveled in a circle (pedaling rate in rpm * 2 * pi * crank length in
meters / 60 gives a measure of pedal speed in meters per second). That is,
the cost or efficiency for any given pedal speed was the same regardless of
crank length. So if you like to use 175mm cranks and pedal at 75rpm but for
some reason you find yourself on a bike with 170mm cranks, you will achieve
the same efficiency by pedaling at 77.2rpm (pedaling rate * 175/170). Or if,
as Andrew suggested and I agreed, you want to use shorter cranks in order to
achieve a more aero position, then you could use 165mm cranks and pedal at
79.5rpm. The only problem is that you might not find the gear you want
unless you change your chain ring by one to three teeth. You'll produce the
same power for any given VO2 with any of those combinations.
Cheers,
Jim
Callas
> I'm 5'9"(176 cm) with an inseam of 31"(79 cm). I use a 175 mm crank. I
> never realized it until now, but according to all the measurement
> theory, I should be using a 168.5 or 170 mm crank. I really don't
> understand the logic behind this as the 175 mm feels fine. But then, I
> really don't know anything different on my bike. Also, according to
> basic lever action physics, would there not be a power advantage using a
> slightly longer crank? My wife has a 168.5 crank on her bike. When I've
> been on it, it feels like I'm spinning too much.
The chances are you're under-spinning on 175. 168.5 will *feel* like
over-spinning but it will be because you're comparing it to under-
spinning.
IMO, it's very hard to over-spin - I think goal cadence should be as high
as is reasonably sustainable.
--
Callas
Callas
>
> "Neal L. Grotenstein" <ne...@cpcug.org> wrote in message
> news:Pine.GSO.3.96.101092...@cpcug.org...
> > --Personal note: I'm 5'7" and buy pants with leg lengths of 29 or 30"
> > difference - it just felt too big. I happily returned to 170mm.
>
> clip. Wow!
Imagine the circle described by a crank 170mm. Imagine the area of that
circle.
Now imagine the area of the circle described by a crank of 171mm. The
difference is *not* 1mm.
This difference in area is why a 2.5 or even 1mm difference has such a
noticeable effect.
--
Callas
John Forrest Tomlinson
news:MPG.161a80637...@news-central.giganews.com...
> IMO, it's very hard to over-spin -
> I think goal cadence should be as high
> as is reasonably sustainable.
Any ideas why?
JT
--
*******************************************
NB: reply-to address is munged
Visit http://www.jt10000.com
*******************************************
Peter Cole
Why is the swept area significant? I would think only the circumference
would matter, and that is proportional to the radius, so 1 mm is still less
than 1% different.
Sheldon Brown
> > > The paper on submaximal metabolic cost (i.e. endurance performance
> > > power) is in review right now and should be out sometime next year. The
> > > results indicate no significant effect of crank length so, again, pick
> > >any length you like.
Phil Holman asked:
> > What about cadence and submaximal power. Lots out there that use
> > longer cranks to grind a bigger gear at a lower cadence????
Jim replied:
> That's a good point. Our results indicated that the main predictor of submax
> cost (i.e. the metabolic cost of producing power) was the speed at which the
> pedal traveled in a circle (pedaling rate in rpm * 2 * pi * crank length in
> meters / 60 gives a measure of pedal speed in meters per second). That is,
> the cost or efficiency for any given pedal speed was the same regardless of
> crank length.
This is also the central point of gain ratio, which is the ratio of
ground speed to pedal speed.
Viewed another way, it is the ratio of pedal force (circumferential
component) and drive force at the drive wheel.
Sheldon "http://sheldonbrown.com/gain.html" Brown
+---------------------------------------+
| There's nothing like not being dead |
| to improve a fellow's outlook. |
| -- Michael Flynn |
+---------------------------------------+
David L. Johnson
> Imagine the circle described by a crank 170mm. Imagine the area of that
> circle.
>
> Now imagine the area of the circle described by a crank of 171mm. The
> difference is *not* 1mm.
>
> This difference in area is why a 2.5 or even 1mm difference has such a
> noticeable effect.
What earthly importance does the _area_ have? You could just as well suggest
raising the radius to the tenth power for all the significance that would
have. The foot, attached to the pedal, follows along the circle, so the only
significance would be the circumference of the circle. Now, a change from 170
to 171 is a change of 0.58%, and the relative change of the circumference is
also, not so surprizingly, 0.58%. It's still a princess-and-the-pea
difference.
--
David L. Johnson
__o | You will say Christ saith this and the apostles say this; but
_`\(,_ | what canst thou say? -- George Fox.
(_)/ (_) |
Callas
> "Callas" <cal...@summerblue.net> wrote:
> > IMO, it's very hard to over-spin -
> > I think goal cadence should be as high
> > as is reasonably sustainable.
>
> Any ideas why?
Only rationalisations of my personal experience.
I find the faster I spin, the less force I have to exert to maintain a
given speed. My lungs and heart work more and my legs less. IME, lungs
and heart can work pretty much forever, but legs have a definite limited
life span :)
But this just reflects my personal geometry, probably.
--
Callas
Callas
> "Callas" <cal...@summerblue.net> wrote:
> > > You "felt" the 1mm difference? That's about the thickness of a paper
> > > clip. Wow!
> > Imagine the circle described by a crank 170mm. Imagine the area of that
> > circle.
> > Now imagine the area of the circle described by a crank of 171mm. The
> > difference is *not* 1mm.
> > This difference in area is why a 2.5 or even 1mm difference has such a
> > noticeable effect.
> Why is the swept area significant? I would think only the circumference
> would matter, and that is proportional to the radius, so 1 mm is still less
> than 1% different.
You're right, but that circumference is being pedalled - it's being moved
around in the circle every time you make a revolution of the pedals. And
it's pedalling where you put the effort in - where you notice the
difference. It's the multiplier of the circumference, to use the words
loosely.
--
Callas
Callas
> Callas wrote:
>
> > Imagine the circle described by a crank 170mm. Imagine the area of that
> > circle.
> >
> > Now imagine the area of the circle described by a crank of 171mm. The
> > difference is *not* 1mm.
> >
> > This difference in area is why a 2.5 or even 1mm difference has such a
> > noticeable effect.
>
> What earthly importance does the _area_ have? You could just as well suggest
> raising the radius to the tenth power for all the significance that would
> have. The foot, attached to the pedal, follows along the circle, so the only
> significance would be the circumference of the circle. Now, a change from 170
> to 171 is a change of 0.58%, and the relative change of the circumference is
> also, not so surprizingly, 0.58%. It's still a princess-and-the-pea
> difference.
I read the comments about self-deceptive perception of difference after I
posted, and I agree with them. I'm quite into audio equipment and there
is a *lot* of false non-blind data going around. IMO, if it's not a
blind test, your data is invalid.
Back to the crank length - when you pedal, your feet are pushing the
pedals around. Taking one revolution as a basic unit of work, it seems
to me that the effort involved in that revolution, when the crank length
changes, relates much more strongly to the area covered by the crank
during its revolution than the simple length of the crank.
It's a bit like navel shells. A 5 inch shell is a *lot* more powerful
than a 4 inch shell. A 6 inch shell is a lot lot more powerful than a 5
inch shell. Power is non-proportional to diameter.
Likewise, effort required is non-proportional to crank length; going from
172.5 to 175 is much less extra work than from 175 to 177.5 - even though
the increases in crank length are the same.
--
Callas
Peter Cole
Power = Work / unit time
Navel[sic] shells not withstanding
"Callas" <cal...@summerblue.net> wrote in message
news:MPG.161ac5f7d...@news-central.giganews.com...
and...@thankstomycranks.com
> IMO, it's very hard to over-spin - I think goal cadence should be as high
> as is reasonably sustainable.
Cadence and "spin" of themselves are meaningless goals.
See Jim Martin's post about pedal-speed (which in an overall kind of way
governs muscle-contraction speeds).
It would appear that it is pedal speeds which need to be optimised.
Crank-length and cadence made no difference (at least they were too small
for the experiments to pick up).
Of course, 145mm to 195mm isn't a massive range of lengths.
Doubtless if we'd had 50mm to 300 mm the differences would not have been
lost in the "noise".
--
Andrew Bradley
www.thankstomycranks.com
Tom Kunich
news:3BAABAF8...@on.aibn.com...
> I'm 5'9"(176 cm) with an inseam of 31"(79 cm). I use a 175 mm crank. I
> never realized it until now, but according to all the measurement
> theory, I should be using a 168.5 or 170 mm crank. I really don't
> understand the logic behind this as the 175 mm feels fine. But then, I
> really don't know anything different on my bike. Also, according to
> basic lever action physics, would there not be a power advantage using
a
> slightly longer crank? My wife has a 168.5 crank on her bike. When
I've
> modified by gear ratios? What is the reasoning behind this theoretical
> crank length sizing and how important is it?
There have been a lot of tests run with varying lengths of crank arms.
The results seem to be that whatever you get used to you get your best
performance out of. There doesn't seem to be any specific advantage to,
say, long cranks on a climbing bike and short ones on a track bike aside
from purely mechanical problems such as long cranks being inappropriate
for a track bike due to the pedals hitting the banking.
Tom Kunich
message news:6ZFq7.405869$NK1.39...@bin3.nnrp.aus1.giganews.com...
>
> I can certainly feel a couple millimeters. Not in the size of the
> circle my feet go through, but at the top of the pedal stroke.
I don't believe that John. I can't even tell the difference between
170's and 175's unless I'm spinning really fast.
Sheldon Brown
> > > Imagine the circle described by a crank 170mm. Imagine the area of that
> > > circle.
> > >
> > > Now imagine the area of the circle described by a crank of 171mm. The
> > > difference is *not* 1mm.
> > >
> > > This difference in area is why a 2.5 or even 1mm difference has such a
> > > noticeable effect.
David Johnson asked:
> > What earthly importance does the _area_ have? You could just as well suggest
> > raising the radius to the tenth power for all the significance that would
> > have. The foot, attached to the pedal, follows along the circle, so the only
> > significance would be the circumference of the circle. Now, a change from 170
> > to 171 is a change of 0.58%, and the relative change of the circumference is
> > also, not so surprizingly, 0.58%. It's still a princess-and-the-pea
> > difference.
"Callas" replied:
> Back to the crank length - when you pedal, your feet are pushing the
> pedals around. Taking one revolution as a basic unit of work, it seems
> to me that the effort involved in that revolution, when the crank length
> changes, relates much more strongly to the area covered by the crank
> during its revolution than the simple length of the crank.
It may "seem" that way to you, but there's no mathematical basis for
this belief. Circumference and radius are both linear dimensions, and
are exactly proportional to one another.
> It's a bit like navel shells. A 5 inch shell is a *lot* more powerful
> than a 4 inch shell. A 6 inch shell is a lot lot more powerful than a 5
> inch shell. Power is non-proportional to diameter.
You're comparing apples and locomotives here. Assuming the same shape
shell, mass goes up with the cube of a linear dimension, so your 5 inch
shell will weigh almost twice as much as 4 inch shell of equal
proportions, since each of the 3 dimensions is increased by 25%.
> Likewise, effort required is non-proportional to crank length;
That's not correct. Effort (force) is exactly inversely proportional to
crank length.
> going from 172.5 to 175 is much less extra work than from 175 to 177.5 - even though
> the increases in crank length are the same.
That's doubly incorrect:
膝oing from 172.5 to 175 is an increase of 1.449%, while going from 175
to 177.5 is only a 1.429% increase.
匹hanging the crank lengh has no relationship whatever on the amount of
work done.
Sheldon "Mathematics Has Nothing To Do With Perception Nor Opinion" Brown
+-----------------------------------------------------------+
| The difference between science and the fuzzy subjects |
| is that science requires reasoning while those other |
| subjects merely require scholarship. |
| --Robert A. Heinlein |
+-----------------------------------------------------------+
John Forrest Tomlinson
news:3bb0d7e9$1...@news.cadence.com...
The reason is that I get pain at the top of the pedal stroke if the
angle behind my knee gets smaller than I'm used to.
I built up a new frame a few months ago, for example, and was sloppy
or something slipped a couple mm on the second ride. Felt it right
away and I wasn't looking for the problem. Based on feel I couldn't
say with certainty whether the seat was lower or someone had snuck
into my apartment and put on longer cranks (logic told me it was the
former) but I felt it right away.
So if someone put longer cranks on my bike -- even 2.5 longer -- I'd
notice.
Martin Goldstein
picture of the featured "wrench" who is our own Peter Chisholm aka Vecchio. Run. do
not walk to Borders, etc. and scope out the November issue.
Be well.
Martin
David Balfoort
Is his Shimano tattoo visible?
David
EPMiller
(captain) has 175mm. I have been riding that thing for several years and still
don't like the longer cranks. I just can't afford to replace both sets which I
would have to do because my wife is 4' 10" and the stoker cranks are 170mm.
:-( Also occasionally I do some repair work for friends and when I jump on
and ride one of their bikes I can tell immediately which ones have 175mm cranks.
Anybody want to trade a set of 170mm /175mm tandem cranks for a 165mm/170mm set?
Eric Miller
David L. Johnson
> Back to the crank length - when you pedal, your feet are pushing the
> pedals around. Taking one revolution as a basic unit of work, it seems
> to me that the effort involved in that revolution, when the crank length
> changes, relates much more strongly to the area covered by the crank
> during its revolution than the simple length of the crank.
Why? Seems to me that the work (effort) is related to the force over
distance. But, what do I know.
>
> It's a bit like navel shells. A 5 inch shell is a *lot* more powerful
> than a 4 inch shell.
That's because the power of such a shell is related to its mass, which
increases at least with the area (depends on the design; if it is longer as
well, then the increase in mass, proportional to the volume, will increase
even more).
> A 6 inch shell is a lot lot more powerful than a 5
> inch shell. Power is non-proportional to diameter.
Huh? This has nothing to do with the "power" applied to a bicycle.
--
David L. Johnson
__o | And though I have the gift of prophecy, and understand all
_`\(,_ | mysteries, and all knowledge; and though I have all faith, so
(_)/ (_) | that I could remove mountains, and have not charity, I am
nothing. [1 Corinth. 13:2]
Callas
> "Callas" wrote:
> > Back to the crank length - when you pedal, your feet are pushing the
> > pedals around. Taking one revolution as a basic unit of work, it seems
> > to me that the effort involved in that revolution, when the crank length
> > changes, relates much more strongly to the area covered by the crank
> > during its revolution than the simple length of the crank.
>
> It may "seem" that way to you, but there's no mathematical basis for
> this belief. Circumference and radius are both linear dimensions, and
> are exactly proportional to one another.
Proportional but non-linear, yes?
A diameter of 1cm give a circumference of n; a diameter of 2cm is *not* a
circumference of 2n.
> > It's a bit like navel shells. A 5 inch shell is a *lot* more powerful
> > than a 4 inch shell. A 6 inch shell is a lot lot more powerful than a 5
> > inch shell. Power is non-proportional to diameter.
>
> You're comparing apples and locomotives here. Assuming the same shape
> shell, mass goes up with the cube of a linear dimension, so your 5 inch
> shell will weigh almost twice as much as 4 inch shell of equal
> proportions, since each of the 3 dimensions is increased by 25%.
It wasn't intended to be an exact comparason; I was trying to get the
idea of non-linearity across.
> > Likewise, effort required is non-proportional to crank length;
>
> That's not correct. Effort (force) is exactly inversely proportional to
> crank length.
> > going from 172.5 to 175 is much less extra work than from 175 to 177.5 - even though
> > the increases in crank length are the same.
>
> That's doubly incorrect:
>
> 膝oing from 172.5 to 175 is an increase of 1.449%, while going from 175
> to 177.5 is only a 1.429% increase.
Those percentages are the change in length of the crank as you go from
172.5 to 175, to 177.5.
What I was trying to say in the original post was that looking only at
the change in length of the crank does not tell you about the change in
effort required to pedal.
I argue that the change in effort required to pedal a crank through one
revolution as the crank length changes is *not* represented by the
difference in length of the crank but rather by the circumference or area
of the circle described.
I think when it gets down to it what I'm talking about is really do with
you how a load is presented to the cyclist. If you ask someone to push
too hard, it's very inefficient.
Crank length (and gearing, and leg length, etc) all relate to this.
> 匹hanging the crank lengh has no relationship whatever on the amount of
> work done.
Yes, I understand this. But the way in which that work is presented to
the human pedaller affects how much effort *HE* has to do to produce the
work done.
--
Callas
Callas
[snip]
Please see reply to Sheldon.
I think part of the confusion here originates in my use of certain words
which have very specific meanings in physics.
--
Callas
Callas
> "Callas" <cal...@summerblue.net> wrote in message
> > You're right, but that circumference is being pedalled - it's being moved
> > around in the circle every time you make a revolution of the pedals. And
> > it's pedalling where you put the effort in - where you notice the
> > difference. It's the multiplier of the circumference, to use the words
> > loosely.
> Work = Force x Distance
> Power = Work / unit time
Reminds me never to use the word "work" again in the company of people
with a physics background :)
> Navel[sic] shells not withstanding
Quite so. But humans have optimal ways of generating effort and if your
crank length is too long, you push yourself into a non-optimal situation.
It's very similar really to using the wrong gear.
--
Callas
Nora Lenderby
> Proportional but non-linear, yes?
>
> A diameter of 1cm give a circumference of n; a diameter of 2cm
> is *not* a circumference of 2n.
Mister Callas, the words 'linear' and 'proportional' are synonymous. One of
the first rules of geometry that most children are taught is precisely that
which you are disputing here in so amusing a fashion, namely that the
circumference of a circle is proportional to its diameter, the constant of
proportionality being PI. A circle of diameter 1cm has a circumference of
PI cm. A circle of diameter 2cm has a circumference of 2 PI cm. Nothing
could be more trivial.
N. Lenderby (Mrs)
Tom Kunich
news:3BB1182D...@library.syr.edu...
He got drunk while on R & R with a bunch of other pilot buddies and when
he passed out they got that tattoo placed on a, umm, prominent location.
When he sobered up he assumed that he had it put on himself and has
never forgiven his subconscious mind. That is why he is so violently
pro-Campi.
Sheldon Brown
>
> Capt...@sheldonbrown.com wrote:
> > "Callas" wrote:
> > > Back to the crank length - when you pedal, your feet are pushing the
> > > pedals around. Taking one revolution as a basic unit of work, it seems
> > > to me that the effort involved in that revolution, when the crank length
> > > changes, relates much more strongly to the area covered by the crank
> > > during its revolution than the simple length of the crank.
> >
> > It may "seem" that way to you, but there's no mathematical basis for
> > this belief. Circumference and radius are both linear dimensions, and
> > are exactly proportional to one another.
>
> Proportional but non-linear, yes?
No, "proportional" means "linear."
> A diameter of 1cm give a circumference of n; a diameter of 2cm is *not* a
> circumference of 2n.
You're mistaken. A diameter of 1 cm gives a circumference of *, 3.14
cm; a diameter of 2 cm gives a circumference of 2*, 6.28.
It sounds as if you have been out of school too long, and have forgotten
basic primary school math.
> > > It's a bit like navel shells. A 5 inch shell is a *lot* more powerful
> > > than a 4 inch shell. A 6 inch shell is a lot lot more powerful than a 5
> > > inch shell. Power is non-proportional to diameter.
> >
> > You're comparing apples and locomotives here. Assuming the same shape
> > shell, mass goes up with the cube of a linear dimension, so your 5 inch
> > shell will weigh almost twice as much as 4 inch shell of equal
> > proportions, since each of the 3 dimensions is increased by 25%.
>
> It wasn't intended to be an exact comparason; I was trying to get the
> idea of non-linearity across.
It can't be an exact comparision because you're imagining non-linearity
where it doesn't exist. This is not in the realm of opinion, this is
basic math and geometry, for which you are substituting subjective gut
feelings. Doesn't work that way!
> > > Likewise, effort required is non-proportional to crank length;
> >
> > That's not correct. Effort (force) is exactly inversely proportional to
> > crank length.
>
> > > going from 172.5 to 175 is much less extra work than from 175 to 177.5 - even though
> > > the increases in crank length are the same.
> >
> > That's doubly incorrect:
> >
> > 膝oing from 172.5 to 175 is an increase of 1.449%, while going from 175
> > to 177.5 is only a 1.429% increase.
>
> Those percentages are the change in length of the crank as you go from
> 172.5 to 175, to 177.5.
Exactly.
> What I was trying to say in the original post was that looking only at
> the change in length of the crank does not tell you about the change in
> effort required to pedal.
Yes it does.
> I argue that the change in effort required to pedal a crank through one
> revolution as the crank length changes is *not* represented by the
> difference in length of the crank but rather by the circumference or area
> of the circle described.
I'm afraid you've gotten in over your head, you need some remedial math.
Speaking of "the circumference or area of the circle" shows that you're
not thinking clearly. It _can't_ be both, because the relationship
between circumference and area is non linear. Circumference, like
radius and diamter, is a one-dimensional value. Circumference, radius
and diameter all bear a linear relationship to one another.
Area is a two-dimensional quantity, and is measured in different units
(square cm, for instance, rather than cm.)
> I think when it gets down to it what I'm talking about is really do with
> you how a load is presented to the cyclist.
It is presented by a simple lever/crank.
> If you ask someone to push too hard, it's very inefficient.
That's true, but has nothing to do with your claim...the longer the
crank, the _easier_ it is to push, because you have more leverage.
(This assumes that you change the crank length without changing anything
else. In the real world, the rider would select different gear ratios
to bring the effort (force) back to the comfortable/efficient range.)
> Crank length (and gearing, and leg length, etc) all relate to this.
>
> > 匹hanging the crank lengh has no relationship whatever on the amount of
> > work done.
>
> Yes, I understand this. But the way in which that work is presented to
> the human pedaller affects how much effort *HE* has to do to produce the
> work done.
You haven't made a convincing case for this, and shouting won't help.
Sheldon "Elementary Math" Brown
+------------------------------------------------------------+
| A touchstone to determine the actual worth of an |
| "intellectual"--find out how he feels about astrology. |
| --Robert A. Heinlein |
+------------------------------------------------------------+
Mark M
news:MPG.161bcd688...@news-central.giganews.com...
> > It may "seem" that way to you, but there's no mathematical basis for
> > this belief. Circumference and radius are both linear dimensions, and
> > are exactly proportional to one another.
>
> Proportional but non-linear, yes?
>
> A diameter of 1cm give a circumference of n; a diameter of 2cm is *not* a
> circumference of 2n.
And I thought you were in Cambridge!
Peter Cole
>
> Quite so. But humans have optimal ways of generating effort and if your
> crank length is too long, you push yourself into a non-optimal situation.
>
> It's very similar really to using the wrong gear.
Actually, it's exactly like using the wrong gear, but it's so much easier to
shift gears than switch crank length.
Jim Martin
"Jim Martin" <jma...@xmission.com> wrote in > That's a good point.
>Our results indicated that the main predictor of submax cost (i.e. the
metabolic cost of producing power) was the speed at which the
> pedal traveled in a circle (pedaling rate in rpm * 2 * pi * crank length
in meters / 60 gives a measure of pedal speed in meters per second). That
is,
> the cost or efficiency for any given pedal speed was the same regardless
for
> some reason you find yourself on a bike with 170mm cranks, you will
achieve the same efficiency by pedaling at 77.2rpm (pedaling rate *
175/170). Or if,
> as Andrew suggested and I agreed, you want to use shorter cranks in order
to achieve a more aero position, then you could use 165mm cranks and pedal
at
> 79.5rpm. The only problem is that you might not find the gear you want
unless you change your chain ring by one to three teeth. You'll produce the
> same power for any given VO2 with any of those combinations.
After I posed this, and subsequently read Sheldon's response about "gain
ratio" I got to thinking about typical crank lengths and chain ring
combinations. When I started racing the standard set up on most bikes was
170mm cranks and either a 51 (yes it was a LONG time ago) or 52 chain ring.
Then sometime in the early 80's it became fashionable to have a 53 for a big
chainring. Not long after that bikes started coming equipped with 172.5mm
cranks.
This is pretty interesting because it seems that MAYBE the cranks got longer
(that is people wanted longer cranks) to give the same pedal speed for any
specific rear cog. Or, in Sheldon's "gain ratio" terminolgoy, to return to
the normal gain ratio. So for instance 52 x 15 with 170mm cranks is
approximately equielent to 53 x 15 with 172.5mm cranks. Food for thought.
Cheers,
Jim
Bluto
faster he must pedal on the same length cranks as a shorter rider.
For a rider with more massive legs this does not really make sense to
me. It is also contrary to my observations of different riders'
habits. It's the short folks who tend to spin faster, crank length
notwithstanding.
Chalo Colina
Sheldon Brown <Capt...@sheldonbrown.com> wrote:
> This is a nice analysis, but misses the point. I never asserted that
> Little Man and Big Man need the same gain ratio, and you make a very
> plausible case that they don't.
>
> My point is that either of them can obtain any desired gain ratio
> without varying the crank length, by selecting different gears. If Big
> Man were to shift to a 36 tooth chainring, or to a 22.5 tooth rear
> sprocket (those are even harder to find than 206 mm cranks,
> unfortunately) he'd get the same 4.1 gain ratio without changing crank
> length.
>
> Sheldon "Not Convinced" Brown
> +------------------------------------------------+
> | According to the latest official figures, |
> | 43% of all statistics are totally worthless. |
> +------------------------------------------------+
David L. Johnson
> > Circumference and radius are both linear dimensions, and
> > are exactly proportional to one another.
>
> Proportional but non-linear, yes?
No, proportional and linearly related.
>
> A diameter of 1cm give a circumference of n; a diameter of 2cm is *not* a
> circumference of 2n.
Yes it is. n is, BTW, pi.
> It wasn't intended to be an exact comparason; I was trying to get the
> idea of non-linearity across.
But the nonlinearity is not appropriate, here.
> What I was trying to say in the original post was that looking only at
> the change in length of the crank does not tell you about the change in
> effort required to pedal.
Well, the only additional problem will come from over-flexing the knee. This
is not "extra effort to pedal".
>
> I argue that the change in effort required to pedal a crank through one
> revolution as the crank length changes is *not* represented by the
> difference in length of the crank but rather by the circumference or area
> of the circle described.
Choose. Circumference is linearly related to diameter, area is not. Area is,
however, irrelevant.
--
David L. Johnson
__o | Arguing with an engineer is like mud wrestling with a pig... You
_`\(,_ | soon find out the pig likes it!
(_)/ (_) |
David L. Johnson
trying to argue, so it would be a good idea to use the words with those
specific meanings.
--
David L. Johnson
__o | Become MicroSoft-free forever. Ask me how.
_`\(,_ |
(_)/ (_) |
Tim McNamara
> > I argue that the change in effort required to pedal a crank through one
> > revolution as the crank length changes is *not* represented by the
> > difference in length of the crank but rather by the circumference or area
> > of the circle described.
Err, did you actually take geometry class in high school then? Do you
remember the formula for determining circumference?
C = circumference
r = radius
pi = 3.14159 (*)
C = 2r * pi
Ergo, your argument is self contradictory and of null content, since
the length of the crankarm determines the circumference of the pedaling
circle. You might want to ponder on this and try again.
(*)There is an (hopefully) apocryphal story that a legislator in
Indiana introduced a bill to change the value of pi from an infinitely
repeating value (3.14159...) to 3, in order to make math easier.
David L. Johnson
> pi = 3.14159 (*)
> (*)There is an (hopefully) apocryphal story that a legislator in
> Indiana introduced a bill to change the value of pi from an infinitely
> repeating value (3.14159...) to 3, in order to make math easier.
Um, not quite. pi is not an infinitely repeating decimal. pi is irrational,
and repeating decimals are rational. Sorry, but I had to say that.
I have heard these stories about people in various states trying to legislate
particular values for pi. Usually the value is 22/7, which is pretty close
(3.14286 versus the real value, which begins with 3.14159). Arkansas comes up
in many of them, but I haven't really checked to see if the story is true --
it might well be true and apply in more than one instance. I would not be
surprised if at least such bills had been introduced at various times.
--
David L. Johnson
__o | Some people used to claim that, if enough monkeys sat in front
_`\(,_ | of enough typewriters and typed long enough, eventually one of
(_)/ (_) | them would reproduce the collected works of Shakespeare. The
internet has proven this not to be the case.
Callas
> > Quite so. But humans have optimal ways of generating effort and if your
> > crank length is too long, you push yourself into a non-optimal situation.
> > It's very similar really to using the wrong gear.
> Actually, it's exactly like using the wrong gear, but it's so much easier to
> shift gears than switch crank length.
Yes. Also I would expect crank length to affect your riding position -
the studies mentioned elsewhere in the thread seem to refute that,
though. But I find that hard to believe -> if your crank is 2cm longer,
that will surely affect your saddle position, etc; so getting the length
right is important for your physical comfort and so in turn your
performance.
--
Callas
Callas
> Callas wrote:
> > david....@lehigh.edu wrote:
> > I think part of the confusion here originates in my use of certain words
> > which have very specific meanings in physics.
> Perhaps. You should notice that it is through elementary physics that you are
> trying to argue, so it would be a good idea to use the words with those
> specific meanings.
It's been too many years since I did elementary physics I'm afraid +)
If I could remember the meanings, I would. I ought to look them up again
but it's just not important enough.
--
Callas
Callas
Condescention really is an optional behaviour -> if you think I'm wrong,
you can explain it without having to be so, and if I am wrong, I am; what
of it?
--
Callas
Callas
> Callas wrote:
> > Capt...@sheldonbrown.com wrote:
> > A diameter of 1cm give a circumference of n; a diameter of 2cm is *not* a
> > circumference of 2n.
>
> You're mistaken. A diameter of 1 cm gives a circumference of *, 3.14
> cm; a diameter of 2 cm gives a circumference of 2*, 6.28.
>
> It sounds as if you have been out of school too long, and have forgotten
> basic primary school math.
You're not wrong - what I'm writing is from intuition, I can't remember
the math - it's been a long time. I could look it up but I'm not that
concerned about being right.
> > It wasn't intended to be an exact comparason; I was trying to get the
> > idea of non-linearity across.
>
> It can't be an exact comparision because you're imagining non-linearity
> where it doesn't exist. This is not in the realm of opinion, this is
> basic math and geometry, for which you are substituting subjective gut
> feelings. Doesn't work that way!
Quite so. Ones intuitive belief does not compete with maths.
> > I argue that the change in effort required to pedal a crank through one
> > revolution as the crank length changes is *not* represented by the
> > difference in length of the crank but rather by the circumference or area
> > of the circle described.
>
> I'm afraid you've gotten in over your head, you need some remedial math.
> Speaking of "the circumference or area of the circle" shows that you're
> not thinking clearly. It _can't_ be both, because the relationship
> between circumference and area is non linear.
Well, I was thinking it could have been either, I wasn't sure which one
would be more representative. I appreciate they are different.
> > I think when it gets down to it what I'm talking about is really do with
> > you how a load is presented to the cyclist.
>
> It is presented by a simple lever/crank.
I meant in the sense of being how hard to push as opposed to the exact
mechanism by which the rider pushes.
> > If you ask someone to push too hard, it's very inefficient.
>
> That's true, but has nothing to do with your claim...the longer the
> crank, the _easier_ it is to push, because you have more leverage.
I'm confused - why do people therefore talking about shortening the
cranks to make pedalling easier?
> > Yes, I understand this. But the way in which that work is presented to
> > the human pedaller affects how much effort *HE* has to do to produce the
> > work done.
>
> You haven't made a convincing case for this, and shouting won't help.
No shouting intended; it was an emphasis.
--
Callas
Callas
> "Callas" <cal...@summerblue.net> wrote in message
> news:MPG.161bcd688...@news-central.giganews.com...
> > Proportional but non-linear, yes?
> >
> > A diameter of 1cm give a circumference of n; a diameter of 2cm is *not* a
> > circumference of 2n.
> And I thought you were in Cambridge!
Who said I studied math? :)
--
Callas
Callas
> Callas wrote:
> > A diameter of 1cm give a circumference of n; a diameter of 2cm is *not* a
> > circumference of 2n.
> Yes it is. n is, BTW, pi.
I last did math nine years ago - it shows.
> > What I was trying to say in the original post was that looking only at
> > the change in length of the crank does not tell you about the change in
> > effort required to pedal.
>
> Well, the only additional problem will come from over-flexing the knee. This
> is not "extra effort to pedal".
Indeed, I'm confused ATM. Sheldon said the longer the crank, the easier
it is to push. I remember this from physics. So why *do* people find
shorter cranks easier to cycle with?
> > I argue that the change in effort required to pedal a crank through one
> > revolution as the crank length changes is *not* represented by the
> > difference in length of the crank but rather by the circumference or area
> > of the circle described.
>
> Choose. Circumference is linearly related to diameter, area is not. Area is,
> however, irrelevant.
Yes, I think I'm getting there. Is it in fact reasonable to view the
circle as a continuous application of force to stationary surface?
--
Callas
Callas
> Mr. Callas wrote:
>
> > > I argue that the change in effort required to pedal a crank through one
> > > revolution as the crank length changes is *not* represented by the
> > > difference in length of the crank but rather by the circumference or area
> > > of the circle described.
>
> Err, did you actually take geometry class in high school then? Do you
> remember the formula for determining circumference?
I did, it was a long time ago, and no, I don't.
> Ergo, your argument is self contradictory and of null content, since
> the length of the crankarm determines the circumference of the pedaling
> circle. You might want to ponder on this and try again.
Yes, I have been.
> (*)There is an (hopefully) apocryphal story that a legislator in
> Indiana introduced a bill to change the value of pi from an infinitely
> repeating value (3.14159...) to 3, in order to make math easier.
I heard it was to 4!
--
Callas
and...@thankstomycranks.com
Jim Martin <jma...@xmission.com> wrote in message
news:9otc51$a1e$1...@news.xmission.com...
>
> After I posed this, and subsequently read Sheldon's response about "gain
> ratio" I got to thinking about typical crank lengths and chain ring
> combinations. When I started racing the standard set up on most bikes was
> 170mm cranks and either a 51 (yes it was a LONG time ago) or 52 chain
ring.
> Then sometime in the early 80's it became fashionable to have a 53 for a
big
> chainring. Not long after that bikes started coming equipped with 172.5mm
> cranks.
>
> This is pretty interesting because it seems that MAYBE the cranks got
longer
> (that is people wanted longer cranks) to give the same pedal speed for any
> specific rear cog. Or, in Sheldon's "gain ratio" terminolgoy, to return to
> the normal gain ratio. So for instance 52 x 15 with 170mm cranks is
> approximately equielent to 53 x 15 with 172.5mm cranks. Food for thought.
It's a possibility someone at Campag thought this switch appropriate.
On the track, this might have been justified, assuming a given rider had
the perfect gear to start with, but on the road, with multiple gears and
varying road conditions, "perfect gearing" is an approximate concept. I
doubt if riders could ever determine the "right gears" to such small
tolerances.
What amazes me is that with the vastly differing relative crank-lengths out
there, racers have always tended to carry the same gearing, and these days
(spurred on by their coaches) compare cadences a lot.
--
Andrew Bradley
http://www.thankstomycranks.com
and...@thankstomycranks.com
Nora Lenderby <nora_l...@hotmail.com> wrote in message
news:9osgrp$bs7$1...@newsg1.svr.pol.co.uk...
> Mister Callas, the words 'linear' and 'proportional' are synonymous.
You are making gender assumptions here Mrs Lenderby. Do you have any
justification for these?
Nora Lenderby
news:R_Ds7.1023$bi6.16252@stones...
> Nora Lenderby <nora_l...@hotmail.com> wrote in message
> news:9osgrp$bs7$1...@newsg1.svr.pol.co.uk...
> > Mister Callas, the words 'linear' and 'proportional' are synonymous.
> You are making gender assumptions here Mrs Lenderby.
No I am not.
N. Lenderby (Mrs)
and...@thankstomycranks.com
Mark M <m...@sink.drain> wrote in message
news:x5ns7.8491$L4.15...@news6-win.server.ntlworld.com...
Don't be callous with our Callas, Doc.
(Unless, of course he's your alias).
and...@thankstomycranks.com
under discussion, there are some questions I have been pondering, which
could perhaps be answered in the lab (the necessary data may even be there
already, but I haven't seen it presented from this angle):-
1) The relationship between leg-length and optimal cadence (max power and/or
aerobic).
2) The relationship between leg-length and max cadence
3)Differences in (average) muscle-fibre composition (sarcomer count and
sarcomer length) between the short and the tall.
(Have you any cadavers lying around in the lab, Jim?)
All these on a 170mm crank.
In other words, indication as to whether prescribing cadences for riders to
use is meaningful in the 170-for-all world we basically live in..
Nearly all the smaller riders I have raced with seem to use low cadences,
and based on a "same muscle fibres" assumption, this is theoretically
predictable.
David L. Johnson
> Indeed, I'm confused ATM. Sheldon said the longer the crank, the easier
> it is to push. I remember this from physics. So why *do* people find
> shorter cranks easier to cycle with?
Crank length is a compromise between leverage (which is improved by longer
cranks) and the ability to spin (which is improved by shorter cranks). If
your cranks were very long, you could not maintain a decent spin, which is
necessary for endurance. If they were very short, then you would need to use
very low gears, and hence very high spin, to get enough leverage.
> Yes, I think I'm getting there. Is it in fact reasonable to view the
> circle as a continuous application of force to stationary surface?
I have no idea what you mean by that.
--
David L. Johnson
__o | "What am I on? I'm on my bike, six hours a day, busting my ass.
_`\(,_ | What are you on?" --Lance Armstrong
(_)/ (_) |
Jean
http://hctr.be.cua.edu/kirtley/be522/tempspat/
Jean
<and...@thankstomycranks.com> wrote in message
news:tiGs7.136$V21.718@wards...
and...@thankstomycranks.com
Jean <cj...@spam.not> wrote in message
news:XtIs7.428$Cu2....@eagle.america.net...
Yes, very interesting. Was there a particular point to note with respect to
the current debate?
Tim McNamara
<david....@lehigh.edu> wrote:
> Tim McNamara wrote:
>
> > pi = 3.14159 (*)
>
> > (*)There is an (hopefully) apocryphal story that a legislator in
> > Indiana introduced a bill to change the value of pi from an infinitely
> > repeating value (3.14159...) to 3, in order to make math easier.
>
> Um, not quite. pi is not an infinitely repeating decimal. pi is irrational,
> and repeating decimals are rational. Sorry, but I had to say that.
Yes, thank you. You are quite correct. I am always rather bemused by
the efforts to compute pi to thousands of decimal places as it seems of
little practical value other than perhaps to practice programming and
spend a lot of processor cycles.
Tim McNamara
wrote:
> In other words, indication as to whether prescribing cadences for riders to
> use is meaningful in the 170-for-all world we basically live in..
Humm. Most the bikes sold around here (at least road bikes and MTBs)
seem to come with 175's by default. Is that not the case in the UK?
Mark M
news:tiGs7.135$V21.843@wards...
>
> Mark M <m...@sink.drain> wrote in message
> news:x5ns7.8491$L4.15...@news6-win.server.ntlworld.com...
> > "Callas" <cal...@summerblue.net> wrote in message
> > news:MPG.161bcd688...@news-central.giganews.com...
> >
> > > > It may "seem" that way to you, but there's no mathematical basis for
> > > > this belief. Circumference and radius are both linear dimensions,
and
> > > > are exactly proportional to one another.
> > >
> > > Proportional but non-linear, yes?
> > >
> > > A diameter of 1cm give a circumference of n; a diameter of 2cm is
*not*
> a
> > > circumference of 2n.
> >
> > And I thought you were in Cambridge!
>
> Don't be callous with our Callas, Doc.
Well, he/she/it seems to cycle within spitting distance of Newton's old
haunts, but have precious little regard for the old bloke. "Not important
enough right now" sort of stuff.
> (Unless, of course he's your alias).
Not one of my aliases. Whether he's a real Callas I can't know that unless
I can hear him sing....
Doc
PS It wasn't Maria's real name though.
Mark M
Osmosis should have been enough!
Now get back to those cleats man!
David L. Johnson
> I am always rather bemused by
> the efforts to compute pi to thousands of decimal places as it seems of
> little practical value other than perhaps to practice programming and
> spend a lot of processor cycles.
There are some of my colleagues who feel the need to justify the money they
asked for for computer support, I guess. It's not like those cpu cycles are
in high demand these days. Lots of things are done with spare cpu time:
searches for large prime numbers, SETI, etc. Me, I save the computer for
important things, like e-mail and newsgroups.
--
David L. Johnson
__o | Become MicroSoft-free forever. Ask me how.
_`\(,_ |
(_)/ (_) |
Phil Holman
> (that is people wanted longer cranks) to give the same pedal speed for any
> specific rear cog. Or, in Sheldon's "gain ratio" terminolgoy, to return to
> the normal gain ratio. So for instance 52 x 15 with 170mm cranks is
> approximately equielent to 53 x 15 with 172.5mm cranks. Food for thought.
And I've been doing some......
I've done a test where I start off at 150 watts and 60rpm and record
my heart rate at various candences up to 120rpm at the same 150 watt
power output.
150watts at 120rpm is so much harder than 150 watts at 60rpm.
IIRC I recorded a 7 or 8 HR difference when going from 100 to 110 rpm
at the same 150watts.
From what you are saying there would be little difference if I went
from 100rpm with 180 cranks to 110rpm with 165 cranks at the same
power output. If I can get some 165s I would like to try this. I have
no vested interest in the result but I want to know if the cost of
pedaling is related to just rpm or footspeed.
An article in pubmed claimed the cost of pedaling at 60rpm was about
20 watts for an average size person and increased approx. as a
function of cadence cubed.
Phil Holman
Matthew Temple
I had another question that perhaps someone here can answer.
Even though you can get the same gear ratios with 165, 170 or 175 mm
crank arms and the appropriate cassette, might there be some
physical advantage to pedaling in either smaller or larger circles?
(Subjectively, 165 mm cranks sure do feel different from 175.)
m
--
=============================================================
Matthew Temple Tel: 617/632-2597
Director, Research Computing Fax: 617/632-4012
Dana-Farber Cancer Institute m...@research.dfci.harvard.edu
44 Binney Street, JF 314 http://research.dfci.harvard.edu
Boston, MA 02115 Choice is the Choice!
Tim McNamara
Holman <phi...@earthlink.net> wrote:
> I've done a test where I start off at 150 watts and 60rpm and record
> my heart rate at various candences up to 120rpm at the same 150 watt
> power output.
I'm curious about how you are doing this test- how you are measuring
watts and what your procedure is.
> 150watts at 120rpm is so much harder than 150 watts at 60rpm.
Interesting, since in terms of work watts is watts. The difference in
perceived exertion is from some other variable. When you say "harder,"
what do you mean?
> An article in pubmed claimed the cost of pedaling at 60rpm was about
> 20 watts for an average size person and increased approx. as a
> function of cadence cubed.
IIRC an article in Bicycling Magazine about 20 years ago claimed that
ergometer studies had resulted in the observation that the "most
efficient" cadence was 60-70 rpm. I don't remember how "most
efficient" was defined.
Jim Martin
"Phil Holman" <phi...@earthlink.net> wrote in message
news:7a4a1cb1.01092...@posting.google.com...
> From what you are saying there would be little difference if I went from
100rpm with 180 cranks to 110rpm with 165 cranks at the same
> power output.
Yes, if you can match power and pedal speed while cycling with those two
crank lengths you should see the same metabolic response (e.g. heart rate).
> An article in pubmed claimed the cost of pedaling at 60rpm was about 20
watts for an average size person and increased approx. as a function of
cadence cubed.
Perhaps, but no previous researchers had used a wide range of crank lengths
to differentiate the effects of pedaling rate from those of pedal speed.
That is where our research built on previous work. Our findings suggest that
the previously reported effects of pedaling rate were really the effects of
pedal speed.
Also, these results only apply to submaximal cycling. During maximal cycling
both pedaling rate (which influences muscle excitation) and pedal speed
(which constrains muscle shortening velocity) influence maximal power.
Cheers,
Jim
and...@thankstomycranks.com
Tim McNamara <tim...@mac.com> wrote in message
news:270920012214508370%tim...@mac.com...
>
> > 150watts at 120rpm is so much harder than 150 watts at 60rpm.
>
> Interesting, since in terms of work watts is watts. The difference in
> perceived exertion is from some other variable. When you say "harder,"
> what do you mean?
There is watts in and watts out and a complex system in between.
You take up more oxygen at higher cadences (foot-speed would be a better
variable)
Have you been here?
http://www.bsn.com/Cycling/articles/cadence.html
Andrew Bradley
Ben Coleman
Callas wrote in message ...
>david....@lehigh.edu wrote:
>> Callas wrote:
>
>
>Yes, I think I'm getting there. Is it in fact reasonable to view the
>circle as a continuous application of force to stationary surface?
>
>--
>Callas
I think I know what you mean. For any given moment in time, the crank is a
set length lever acting on the BB spindle. However, the forces acting on it
vary considerably in the course of a revolution. Maximum downward force at
around 3 o'clock (RHS crank) and maximum upward or minimum downward
somewhere around 9 o'clock.
As far as spinning the cranks is concerned, only the part of the force
acting at 90 degrees to the crank at each moment contributes usefully. So,
if you mapped this over a full revolution, you could draw a continuous
"circle of force" with the radius of the crank, but although the circle is
continuous, the size of the force varies around the circle. So, for any
instant in time, you can take a snapshot of the lever and force acting at
that moment and work out the torque (turning force) acting on the BB
spindle.
Hopefully that answers your question....
Ben
Andrew Coggan
Phil Holman wrote:
> "Jim Martin" <jma...@xmission.com> wrote in message news:<9otc51>
> > This is pretty interesting because it seems that MAYBE the cranks got longer
> > (that is people wanted longer cranks) to give the same pedal speed for any
> > specific rear cog. Or, in Sheldon's "gain ratio" terminolgoy, to return to
> > the normal gain ratio. So for instance 52 x 15 with 170mm cranks is
> > approximately equielent to 53 x 15 with 172.5mm cranks. Food for thought.
>
> And I've been doing some......
> I've done a test where I start off at 150 watts and 60rpm and record
> my heart rate at various candences up to 120rpm at the same 150 watt
> power output.
> 150watts at 120rpm is so much harder than 150 watts at 60rpm.
> IIRC I recorded a 7 or 8 HR difference when going from 100 to 110 rpm
> at the same 150watts.
This is entirely predictable, given that efficiency decreases above a certain
cadence (which is dependent on power output, but at 150 W is likely quite low).
> From what you are saying there would be little difference if I went
> from 100rpm with 180 cranks to 110rpm with 165 cranks at the same
> power output. If I can get some 165s I would like to try this. I have
> no vested interest in the result but I want to know if the cost of
> pedaling is related to just rpm or footspeed.
Since Jim has already made the measurements, on a much larger number of subjects
than just n=1 and using a direct measure of metabolic cost (i.e., VO2) rather than
an indirect indicator (i.e., HR), why would you bother to spend the time?
> An article in pubmed claimed the cost of pedaling at 60rpm was about
> 20 watts for an average size person and increased approx. as a
> function of cadence cubed.
Was that 20 W in metabolic power or 20 W in external power? And how was this
determined: via measuring the cost of unloaded pedaling (not the way to do it,
IMHO), by back-extrapolation from metabolic cost measured at various power
outputs, or via calculation from biomechanical measurements? I suspect that each
would yield different results, but from an applied perspective it isn't really
important...all that really matters is your gross efficiency.
Andy Coggan
and...@thankstomycranks.com
> Was that 20 W in metabolic power or 20 W in external power? And how was
this
> determined: via measuring the cost of unloaded pedaling (not the way to do
it,
> IMHO)
How do you measure the cost of unloaded pedalling?
Mark M
news:duWs7.2622$bi6.28335@stones...
>
> Tim McNamara <tim...@mac.com> wrote in message
> news:270920012214508370%tim...@mac.com...
> >
> > > 150watts at 120rpm is so much harder than 150 watts at 60rpm.
> >
> > Interesting, since in terms of work watts is watts. The difference in
> > perceived exertion is from some other variable. When you say "harder,"
> > what do you mean?
>
> There is watts in and watts out and a complex system in between.
Well, watts consumption and watts output to be precise. The system in
between is complex, but the results of measurements presented here seem not
to be so.
> You take up more oxygen at higher cadences (foot-speed would be a better
> variable)
Also, at higher cadences, one is using different twitch profiles in the
muscle fibres. Is that why you recommend foot speed?
> Have you been here?
> http://www.bsn.com/Cycling/articles/cadence.html
A good reference.
Mark M
Mark M
> Holman <phi...@earthlink.net> wrote:
>
> > I've done a test where I start off at 150 watts and 60rpm and record
> > my heart rate at various candences up to 120rpm at the same 150 watt
> > power output.
>
> I'm curious about how you are doing this test- how you are measuring
> watts and what your procedure is.
I too would be interested in the details of the experimental design.
> > 150watts at 120rpm is so much harder than 150 watts at 60rpm.
>
> Interesting, since in terms of work watts is watts. The difference in
> perceived exertion is from some other variable. When you say "harder,"
> what do you mean?
He means it hurt him more. That's because he's working harder - as well as
putting out the same amount of rear-wheel power, he's doing twice as much
work rotating his legs.
Andrew Bradley has made this same point in terms of oxygen uptake.
> > An article in pubmed claimed the cost of pedaling at 60rpm was about
> > 20 watts for an average size person and increased approx. as a
> > function of cadence cubed.
Incidentally, this would seem to suggest that the power readouts on many
gym-type exercise bikes are wrong, being entirely load-based.
> IIRC an article in Bicycling Magazine about 20 years ago claimed that
> ergometer studies had resulted in the observation that the "most
> efficient" cadence was 60-70 rpm. I don't remember how "most
> efficient" was defined.
The (energy) efficiency of a system is the ratio of the energy it consumes
to its energy output. The human body is more efficient at lower cadence for
the reason mentioned above. But efficiency isn't everything.
Mark M
Mark M
> david....@lehigh.edu wrote:
> > Callas wrote:
> >
> > > Indeed, I'm confused ATM. Sheldon said the longer the crank, the
easier
> > > it is to push. I remember this from physics. So why *do* people find
> > > shorter cranks easier to cycle with?
> >
> > Crank length is a compromise between leverage (which is improved by
longer
> > cranks) and the ability to spin (which is improved by shorter cranks).
If
> > your cranks were very long, you could not maintain a decent spin, which
is
> > necessary for endurance. If they were very short, then you would need
to use
> > very low gears, and hence very high spin, to get enough leverage.
>
>
> > > Yes, I think I'm getting there. Is it in fact reasonable to view the
> > > circle as a continuous application of force to stationary surface?
> >
> > I have no idea what you mean by that.
>
> have the knowledge necessary to see if it's a useful way to think about
> pedalling (or the interest/time to get that knowledge right now).
I think that you are struggling towards having an integral over the circle
of the force applied, and your intuition is that the applied force at a
given point on the circle may vary at different cadences.
Does anyone know if that's why nonrotating cranked systems can offer better
efficiency for some applications?
Mark M
Mark M
> m...@sink.drain wrote:
> > "Callas" <cal...@summerblue.net> wrote:
>
> > > > And I thought you were in Cambridge!
> > > Who said I studied math? :)
> > Osmosis should have been enough!
>
Next thing you'll tell me that it's impossible for a bike to stand on its
spokes.
> > Now get back to those cleats man!
>
> Well - excellent progress, the *right* cleat is now about perfect and
> I'm very happy with it!
Excellent. One day you may get it all sufficiently well adjusted to go out
for a ride!
Mark M
PS Ben Haywards (sale) 6pm Monday - wear your Callas badge, or hum Vissi
D'Arte if you want to be recognised.