Significance of crank arm length?
BillX
bikes have 170mm arms. At 6' would I benefit from buying a new bike with
175mm arms? Is there an equation based on size or length of tibia/femur
that determines what crank arm length is best?
Hjalmar Duklæt
"BillX" <ibru...@aol.com> wrote in message
news:b3ef7q$hj9$1...@ngspool-d02.news.aol.com...
performance would be to small to be noticed. I remember a test I read about
a few years back where they meassured the heart rate at a submaximal effort
using crankarms from 125mm to 200mm. What they found was that it was very
small differences in HR. So for you using170,172.5 or 175 would probably be
the same. My 2c..
Hjalmar
Qui si parla Campagnolo
Not very much unless you are going from 165mm to 180mm or something, and then
it's not 'huge'-
<< My current
bikes have 170mm arms. At 6' would I benefit from buying a new bike with
175mm arms?
Nope, but 172.5 is more 'appropriate' for a person 6 ft tall BUT put three
people in a room and ask about crank length, get four opinions.
<< Is there an equation based on size or length of tibia/femur
that determines what crank arm length is best?
It is VERY subjective..what problem do you want to solve that you are having
with the 170mm cranks??
Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"
Ryan Cousineau
"Hjalmar Duklæt" <ko...@statoil.com> wrote:
What a coincidence! I have another, unrelated reason for wondering about
crank length:
I recently injured my right Achilles tendon in a manner remarkably
similar to what Sheldon Brown describes here:
http://www.sheldonbrown.com/gloss_a.html#ankling
I rode 105 km in one day, by far my longest ride ever. I wasn't trying
to "ankle", but I probably had my seat set a bit too high. I'm
recovering from that injury now, and am working on better technique.
-As compensation, I have moved my pedal cleats back towards the heel of
my shoe, which helps somewhat, and have dropped my seat position
slightly, which helps somewhat. The problem is that I'm also prone to
knee problems, and I think that my new, lower seat height might
contribute to these.
Would going to smaller cranks help? I'm 5'6", ride 51-53 cm frames, and
use 170 mm cranks. I've got an opportunity to pick up some 167.5 cranks
at a good price. Will the 5 mm crank circle diameter change even be
noticeable? I'm thinking yes, since it's close to the size of the saddle
height chances I have made, but was looking for some experienced
opinions.
--
Ryan Cousineau, rcou...@sfu.ca http://www.sfu.ca/~rcousine
President, Fabrizio Mazzoleni Fan Club
BillX
bike. I prefer a rearward saddle position and don't know if that's any
indication on whether my bike crank is too long or short.
Bluto
> Would going to smaller cranks help? I'm 5'6", ride 51-53 cm frames, and
> use 170 mm cranks. I've got an opportunity to pick up some 167.5 cranks
> at a good price. Will the 5 mm crank circle diameter change even be
> noticeable? I'm thinking yes, since it's close to the size of the saddle
> height chances I have made, but was looking for some experienced
> opinions.
I doubt you'll notice the difference in crank circle diameter unless
the 170mm arms you've been using are detrimentally long for you
(causing you to move some parts of your body other than your legs in
order to perform your pedal stroke).
There is some threshold at which a crank becomes too long, for
instance when one's knees hit one's chest while riding in the drops,
or when the knee at the top of the pedal stroke begins to bind and
resist further bending. Whatever this threshold, it is certain and
identifiable for any given rider and bike.
There is no real firm threshold of what constitutes a
shorter-than-optimal length crank, only subtle efficiency issues and
"feel" concerns. But there is such a thing as a too-short crank; for
instance imagine pedaling a 50mm crank. No compensatory gearing would
make that crank length efficient or comfortable for an adult rider of
any size.
I postulate that the "best" crank length for any rider/bike
combination is the longest one that gives no ill effects. However,
it's clearly preferable to err on the short side of that length than
to exceed it by even a little bit.
I believe that "normal" crank lengths in the range of 165-180mm are
sized to fall into the loose zone of "definitely not too long" for
riders of average size.
IMO it's unlikely that even at 5'6" your legs are too short to pedal
properly with 170mm cranks. You are, of course, the one who gets to
make that judgement. But my advice to you is, if you think that 170mm
cranks are actually too long for you, then why shorten them by only
2.5mm? Why not 165mm or even 155mm cranks? There's no point in
almost addressing a suspected problem when you could be certain about
it.
Legs vary in length by much more than the 8-9% difference between
"very short" (165mm) and "very long" (180mm) crankarms. If your leg
length is outside of the middle 10% of the overall range, it stands to
reason that you might be better served by a crank that is shorter or
longer than Shimano and Campagnolo supply.
Dotek is a manufacturer of many inexpensive shorter-than-165mm cranks
frequently used by child BMX racers. Most such cranks I've seen are
of the 110mm double-ring, low-Q-factor type.
Chalo Colina
Wayne T
with no complaints. Builder suggested that since I have to change my crank,
I should go to a 175mm. Would you agree, or would it be best to leave it
alone? I'd love it if it gave me more torque, but when checking a ruler, it
seems so insignificant a change. If there is a negative, it would be when I
am down on the drops because my knees tend to bump against my chest.
"Qui si parla Campagnolo" <vecc...@aol.com> wrote in message
news:20030225085825...@mb-me.aol.com...
Jon Isaacs
>combination is the longest one that gives no ill effects. However,
>it's clearly preferable to err on the short side of that length than
>to exceed it by even a little bit.
The studies that have been show that cranklength is not a performance issue.
In my view cranklengh is really a frame design issue, longer cranks are more
likely to hit when cornering and are more likely to cause pedal overlap with
the front tire.
So, it is really the geometry of the bike that determines the optimal crank
length.
Personally I have a set of 152's that I have used on a few occasions.
Definitely odd.
Jon Isaacs
Jon Isaacs
>with no complaints. Builder suggested that since I have to change my crank,
>I should go to a 175mm. Would you agree, or would it be best to leave it
>alone? I'd love it if it gave me more torque, but when checking a ruler, it
>seems so insignificant a change.
If you want more torque at the rear wheel, then simply change gears, this is
all that a longer crank accomplishes. Your leg pushes with the same force and
does the same amount of work regardless of how you achieve this change. As was
previously pointed out and as your ruler showed you, the difference is small,
it is like going from a 17 tooth cog to a 17.5 tooth cog.
jon isaacs
Qui si parla Campagnolo
a new
bike. I prefer a rearward saddle position and don't know if that's any
indication on whether my bike crank is too long or short.
I would probably recommend a 172.5 for you-
Harris
> I am 6'4" with a 34" inseam. I have ridden with 170mm cranks since 1970
> with no complaints. Builder suggested that since I have to change my crank,
> I should go to a 175mm. Would you agree, or would it be best to leave it
> alone? I'd love it if it gave me more torque, but when checking a ruler, it
> am down on the drops because my knees tend to bump against my chest.
Is that 34" inseam from floor to crotch using the book method or is it
your trouser size? Sounds like you have a long torso if the 34" inseam is
correct.
If you're buying new cranks anyway, you might want to try 175's. But don't
expect a big difference. I've used 170, 172.5, and 175 mm cranks on
various bikes (35.5" inseam). I prefer 175's but the difference is subtle.
Art Harris
S. Delaire "Rotatorrecumbent"
remember were I saw it though.
Lance runs 175 and he is less then 6' tall.
Wind tunnel tests we have done have shown that shorter cranks disturbed the air
flow less, so available power is used more efficient.
Another thing to consider is that for every 5 mm change in crank length the
angular movement of the knee changes by 5 degrees (calculated from my leg
dimensions). If sore knees are a problem try shorter cranks.
Good rule of thumb is "go for what you know" i.e. if current cranks work, don't
change.
Happy cycling
Speedy
BillX wrote:
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NeauDL
tendinitis cleared up. I bet you can tell a difference with this small change.
Anyway, if you're worried about it, just don't sell the longer cranks until
you've had the chance to try the shorter ones.
L. D. Lide
jobst....@stanfordalumni.org
L. D. Lide seems to have an identity problem. Maybe shyness.
In any case, the experiment is a classic of failure to show
relationship between apparent cause and suspected effect (or in new
speak: cause and impact). I see no connection between a 2.5mm change
in crank length and the lack of tendinitis. Repetition of such tales
gives them a life of their own in the rumor pot.
Jobst Brandt
jobst....@stanfordalumni.org
Palo Alto CA
Bluto
>
> The studies that have been show that cranklength is not a performance issue.
Then you'll be using those 50mm cranks I talked about, eh?
Of course it's a performance issue. If 50mm cranks are unusable and
125mm cranks impose a performance penalty on an adult-sized rider,
that implies that there is a "right" length, since we already know
that too-long cranks are unworkable.
Just as a 5'6" rider would be functionally impaired by 136mm cranks,
so is Peter Cole at 6'10" giving up some efficiency with his 170mm
cranks, because they are the proportional equivalent.
If there were not a performance difference between different-length
cranks, then racers would be riding shorter ones with matching lower
BBs. It would allow them a lower, more aerodynamic projected area,
sharper handling, and lighter/stronger cranks, BBs, and frames.
Most successful bicycle racers have been about the same size for the
history of the sport. I expect that 170mm is a good approximation of
the optimum crank length for that average size.
> In my view cranklengh is really a frame design issue, longer cranks are more
> likely to hit when cornering and are more likely to cause pedal overlap with
> the front tire.
>
> So, it is really the geometry of the bike that determines the optimal crank
> length.
It's the geometry of the bike that limits usable crank length. That's
yet another reason that bike wheelbase should be proportional to seat
tube length.
> Personally I have a set of 152's that I have used on a few occasions.
> Definitely odd.
Probably slower than 175s for you, too.
Chalo Colina
Bruce Dickson
http://link.springer-ny.com/link/service/journals/00421/contents/01/00400/index.html
and they stated:-
"Even though maximum cycling power was significantly affected by crank
length, use of the standard 170-mm length cranks should not
substantially compromise maximum power in most adults."
So if they're saying "cycling power was significantly affected by
crank length" I don't think you can say "The studies that have been
show that cranklength is not a performance issue"
It would seem to me that if your height and leg length are
significantly different to most adults maximum power will be
substatially compromised by using standard 170mm cranks and perhaps
even if your are like most adults (5'6" is a little less than average)
it might be slightly compromised. Even if changing your crank length
increased your power by only 1% (and in the study it varied by 5% over
the full range of lengths) or even if it just made you feel more
comfortable it could be worth trying a different length. Considering
what some people will spend on things that you don't need research to
say won't make them go any faster.
Personally I'm significantly taller than most adults (192cm) and ride
185mm cranks and am more powerful and more comfortable than I was on
170mm and 175mm cranks.
Bruce Dickson
Wayne T
"Bruce Dickson" <bjk...@yahoo.com.au> wrote in message
news:b2107252.03022...@posting.google.com...
What is your Inseam?
>
> Bruce Dickson
Tom Paterson
>Even if changing your crank length
>increased your power by only 1% (and in the study it varied by 5% over
>the full range of lengths) (snip)
Those lengths were 120-220mm, far beyond the "normal" 165-175 lengths commonly
available. In that light, 5% difference in power production, esp. considering
habituation in "trained" subjects (implying people who used mostly 170-175mm
cranks in daily life) maybe isn't surprising.
Further, quoting from the J. Martin study, (your link):
<Trained cyclists (n=16) performed maximal inertial load cycle ergometry using
crank lengths of 120, 145, 170, 195, and 220 mm. Maximum power ranged from a
low of 1149 (20) W for the 220-mm cranks to a high of 1194 (21) W for the
145-mm cranks. Power produced with the 145- and 170-mm cranks was significantly
(P<0.05) greater than that produced with the 120- and 220-mm cranks.>
There's no info about leg lengths of the 16 cyclists, but note the shorty 145's
gave the highest power rating, the longest 220's the lowest power.
(unsnip)
>or even if it just made you feel more
>comfortable it could be worth trying a different length.
I'd suggest that for most of us "comfort is everything" (i.e., those not
planning to give Museeuw a hard time this Saturday).
>Personally I'm significantly taller than most adults (192cm) and ride
>185mm cranks and am more powerful and more comfortable than I was on
>170mm and 175mm cranks.
I wouldn't dispute the comfort report but how have you measured "more
powerful"?
--Tom Paterson
one of the six billion
<jobst....@stanfordalumni.org> wrote in message
news:KWd7a.68730$Ik.30...@typhoon.sonic.net...
Since I have the exact same experience I guess the rumor pot gets another
tale.
Peter Cole
news:8b4b7de4.03022...@posting.google.com...
> joni...@aol.com (Jon Isaacs) wrote:
> >
> > The studies that have been show that cranklength is not a performance
issue.
>
> Then you'll be using those 50mm cranks I talked about, eh?
>
> Of course it's a performance issue. If 50mm cranks are unusable and
> 125mm cranks impose a performance penalty on an adult-sized rider,
> that implies that there is a "right" length, since we already know
> that too-long cranks are unworkable.
>
> Just as a 5'6" rider would be functionally impaired by 136mm cranks,
> so is Peter Cole at 6'10" giving up some efficiency with his 170mm
> cranks, because they are the proportional equivalent.
If someone would lend me a computrainer equipped with "varicranks" ($500),
perhaps we could put this matter to rest, once and for all. Of course even
these only go to 185, "proportionally", I should have 210's or something. Oh
well, I'll just hobble along.
http://www.computrainer.com/varicrank.asp
Jon Isaacs
>125mm cranks impose a performance penalty on an adult-sized rider,
>that implies that there is a "right" length, since we already know
>that too-long cranks are unworkable.
The thing to realize is that there have actually been studies done on this very
issue. And whatever you or I want to rationalize, it seems that over a wide
range of crank lengths, I believe the range was something like 130 mm to over
200 mm, there is little difference in efficiency.
>Just as a 5'6" rider would be functionally impaired by 136mm cranks,
>so is Peter Cole at 6'10" giving up some efficiency with his 170mm
>cranks, because they are the proportional equivalent.
This is your assumption and it does seem reasonable but apparently the data
does not support this conclusion.
>It's the geometry of the bike that limits usable crank length. That's
>yet another reason that bike wheelbase should be proportional to seat
>tube length.
Longer wheelbase bicycles have other issues like slower handling, longer
turning radii, etc. Since these are already issues for taller bikes, crank
length becomes one of the variables.
My personal view on crank length is that one is free to choose what seems best
because it really does not matter.
jon isaacs
Tom Paterson
>The thing to realize is that there have actually been studies done on this
>very
>issue. And whatever you or I want to rationalize, it seems that over a wide
>range of crank lengths, I believe the range was something like 130 mm to over
>200 mm, there is little difference in efficiency.
This is a link to the Martin study abstract:
<http://link.springer-ny.com/link/service/journals/00421/contents/01/00400
/index.html
<Abstract. The purpose of this investigation was to determine the effects of
cycle crank length on maximum cycling power, optimal pedaling rate, and optimal
pedal speed, and to determine the optimal crank length to leg length ratio for
maximal power production. Trained cyclists (n=16) performed maximal inertial
load cycle ergometry using crank lengths of 120, 145, 170, 195, and 220 mm.
Maximum power ranged from a low of 1149 (20) W for the 220-mm cranks to a high
of 1194 (21) W for the 145-mm cranks. Power produced with the 145- and 170-mm
cranks was significantly (P<0.05) greater than that produced with the 120- and
220-mm cranks. The optimal pedaling rate decreased significantly with
increasing crank length, from 136 rpm for the 120-mm cranks to 110 rpm for the
220-mm cranks. Conversely, optimal pedal speed increased significantly with
increasing crank length, from 1.71 m/s for the 120-mm cranks to 2.53 m/s for
the 220-mm cranks. The crank length to leg length and crank length to tibia
length ratios accounted for 20.5% and 21.1% of the variability in maximum
power, respectively. The optimal crank length was 20% of leg length or 41% of
tibia length. These data suggest that pedal speed (which constrains muscle
shortening velocity) and pedaling rate (which affects muscle excitation state)
exert distinct effects that influence muscular power during cycling. Even
though maximum cycling power was significantly affected by crank length, use of
the standard 170-mm length cranks should not substantially compromise maximum
power in most adults.>
120-220 lengths, 5% power difference.
The article does suggest an optimal crank/leg length ratio. Note that "trained
cyclists", or one of them anyway, produced the most power on 145's, which can
be assumed to not be the length they ordinarily rode at the time of the study.
--Tom Paterson
Scic
JB wrote:
>> I see no connection between a 2.5mm change in crank length and the lack of
tendinitis. Repetition of such tales gives them a life of their own in the
rumor pot.
"one of the six billion" replied:
>Since I have the exact same experience I guess the rumor pot gets another
tale.
Allow me to add to the pot.
On my bike with 170mm cranks, during a long ride with sustained effort, I often
get a pain deep within the center of my left knee, occassionally followed by
post ride swelling. I have not yet had this condition evaluated.
On my new bike with 175s (admittedly, I was a bit concerned about the length),
in a similar gear and with the same effort, I often reach, but have yet to
pass, the pain threshold. The promise of pain is still there. No swelling, so
far.
I also find it's easier to maintain 20mph with the 175s than the 170s. On the
other hand, I cannot reach the top speed that I can with the 170s. Seems that
I can't spin the 175s fast enough.
Perhaps the psychology of the crank is as important as the physiology.
Sig (Neither shy nor in crisis. Just my preference, thank you.)
Chicago
Calvin
is taller or shorter than average. I am 5' 4.5" (5' 5") My inseam
measures 710.5mm (crudely measured with a string and a 15 cm ruler)
The 20% of leg length formula this article points out would put me on
cranks measuring a whopping 142mm. I'm not sure what I'm on now (only
have a mtn bike) but I will check. If its >170 I will look into
decreasing the length and see what happens.
-calvin
san jose, ca
"Wayne T" <wdu...@ucwphilly.rr.com> wrote in message news:<xCh7a.54395$9i7.3...@twister.southeast.rr.com>...
Jon Isaacs
>length),
>in a similar gear and with the same effort, I often reach, but have yet to
>pass, the pain threshold.
I would be cautious about drawing conclusions about crank length when you are
swapping between 2 bikes. The more valid test is to use the same bike and swap
cranks.
I also suggest it is pretty difficult to see a mechanism that would cause less
knee pain with a longer crank.
>I also find it's easier to maintain 20mph with the 175s than the 170s.
This seems more like the NBS (New Bike Syndrome) than the crank length.
Jon Isaacs
Jay Beattie
> I am 6'4" with a 34" inseam. I have ridden with 170mm cranks since
1970
> with no complaints. Builder suggested that since I have to change my
crank,
> I should go to a 175mm. Would you agree, or would it be best to leave
it
> alone? I'd love it if it gave me more torque, but when checking a
ruler, it
> seems so insignificant a change. If there is a negative, it would be
when I
> am down on the drops because my knees tend to bump against my chest.
I have your dimensions. I like a longer crank -- either 175 or 177.5.
I have absolutely no scientific justification for my preference. I was
originally persuaded to change to a longer crank in about 1976 based
entirely on myth and lore and a Cinelli-driven long crank fad. Hey,
Eddy was using 180s for some events! I have 170s on my track bike, and
they feel cramped. My knees do not explode if I switch between the 170,
175 and 177.5. Try the longer cranks and see what you think (make sure
you can take them back). If you like them, try to work backwards
towards a scientific justification using anecdotes and jargon extracted
from the links provided in this thread. Use phrases like "finite element
analysis." I don't know what it means, but it sounds persuasive. -- Jay
Beattie.
Wayne T
"Jon Isaacs" <joni...@aol.com> wrote in message
news:20030227092301...@mb-cm.aol.com...
Speaking of wheel bases, that reminds me that when I pedal with a pannier
attached to the rear rack, my heal just barely clears that bag. My builder
was suggesting I go from a 170mm crank to a 175mm. Now I know why I will
stay with the 170mm crank.
Bruce Dickson
> powerful"?
I say I'm "more powerful" because I can ride faster on the same rides
(same bike I just changed the cranks). I don't have a power meter
unfortunately. I suppose it is fairly subjective but I'm happy. The
main thing is it just feels heaps better spinning my legs in bigger
circles. I figure if for each hour I ride my feet will spin around
6000 circles I may as well get the radius of the circle right, I would
consider that a far more important factor to bike fit than whether my
hands were 10mm closer or further away but people experiment with
different stems all the time but hardly anyone seems to try different
crank lengths.
I wouldn't try to dismiss anyone's story of reducing knee pain by
changing crank length by as little as 2.5mm. If they say it worked for
them we can hardly tell them they're mistaken. It might only be that
tiny bit more or less knee bend but for most people pedalling at
80-100rpm that's a lot of knee bends.
>there is little difference in efficiency.
As far as I can tell the study was measuring maximun power and did not
measure efficiency, I don't know if anyone has tried.
Bruce Dickson
BTW my inseam is around 91cm (36")
Bill Davidson
> On my bike with 170mm cranks, during a long ride with sustained effort, I often
> get a pain deep within the center of my left knee, occassionally followed by
> post ride swelling. I have not yet had this condition evaluated.
> On my new bike with 175s (admittedly, I was a bit concerned about the length),
> in a similar gear and with the same effort, I often reach, but have yet to
> pass, the pain threshold. The promise of pain is still there. No swelling, so
> far.
There's other variables involved here so I don't know that you can place it all
on crank length. Do you use the same gearing on both bikes? Do you select the
same gears in the same spots under the same conditions? Do the bikes have similar
geometry? Do they have similar weight? Same tires?
> I also find it's easier to maintain 20mph with the 175s than the 170s.
If you're turning the same cadence in the same gear with the same wheel size, then
you should go the same speed. The thing is, with the longer crank, it will require
slightly less torque (but the same amount of energy) to do it. Less torque could
theoretically account for less knee pain and less muscle fatigue.
> On the
> other hand, I cannot reach the top speed that I can with the 170s. Seems that
> I can't spin the 175s fast enough.
Since longer cranks have a larger pedaling circle, they are more difficult to keep
in a good smooth spin; especially if you are not used to the longer crank. I'm
skeptical that 5mm is really all that significant here but YMMV.
> Perhaps the psychology of the crank is as important as the physiology.
I'm sure there's something to that.
--Bill Davidson
--
Please remove ".nospam" from my address for email replies.
Jon Isaacs
>6000 circles I may as well get the radius of the circle right, I would
>consider that a far more important factor to bike fit than whether my
>hands were 10mm closer or further away but people experiment with
>different stems all the time but hardly anyone seems to try different
>crank lengths.
People experiment with different crank lengths all the time, that is what this
thread is about. Many of us have bikes with a variety of crank lengths.
>
>I wouldn't try to dismiss anyone's story of reducing knee pain by
>changing crank length by as little as 2.5mm. If they say it worked for
>them we can hardly tell them they're mistaken. It might only be that
>tiny bit more or less knee bend but for most people pedalling at
>80-100rpm that's a lot of knee bends.
This is a technical forum, so while personal experiences are important, it is
also important to put them in a technical context. When someone gets a new
bike with with slightly longer cranks and then attributes a reduction in knee
pain to the change in crank length without addressing the other issues, it is
questionable. There are many ways small changes or even large changes in
position can affect knee pain and it is extremely difficult to get ones
position identical to another bike. Add to that the fact that longer cranks
increase travel of the knee joints, well, I am doubtful that it is the cranks
that did the trick.
>As far as I can tell the study was measuring maximun power and did not
>measure efficiency, I don't know if anyone has tried.
This is a worthy point. But measuring efficiency is much more difficult. To
measure maximum power all you do is tell em to wind it up. To measure
efficiency, first you have to define efficiency, then you have to measure
various blood levels and oxygen useage at a number of difference would be a
time consuming and expensive study.
Jon Isaacs
Tom Paterson
>I'm
>skeptical that 5mm is really all that >significant here but YMMV.
About 20 years ago (speaking to youthful flexibility, etc.) I tried going from
170's to 175's. Knees hurt through a succession of small saddle adjustments,
stopped hurting when I went back to 170's. This with no "foreshadowing" of such
problems--quite the contrary, expectations of undiluted wonderfulness. I'm even
more comfortable with the 165's I've used for a year and a half or so now. The
Martin study could be viewed as liberating from orthodoxy-- since the measured
power differences between different crank lengths used is pretty small, there
is no "need" to ride any particular length if one is not comfortable with it.
--Tom Paterson
Andy Coggan
news:b2107252.03022...@posting.google.com...
> >there is little difference in efficiency.
>
> As far as I can tell the study was measuring maximun power and did not
> measure efficiency, I don't know if anyone has tried.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=12183473&dopt=Abstract
Andy Coggan
Andy Coggan
news:20030228081815...@mb-cl.aol.com...
> The
> Martin study could be viewed as liberating from orthodoxy-- since the
measured
> power differences between different crank lengths used is pretty small,
there
> is no "need" to ride any particular length if one is not comfortable with
it.
And indeed Jim argues that it may be better to go to shorter, not longer,
cranks for TTing, since it doesn't significantly affect power output, but
can make it easier to achieve a good aero position.
Andy Coggan
Ryan Cousineau
chump...@hotmail.com (Bluto) wrote:
> Ryan Cousineau <rcou...@sfu.ca> wrote:
>
> > Would going to smaller cranks help? I'm 5'6", ride 51-53 cm frames, and
> > use 170 mm cranks. I've got an opportunity to pick up some 167.5 cranks
> > at a good price. Will the 5 mm crank circle diameter change even be
> > noticeable? I'm thinking yes, since it's close to the size of the saddle
> > height chances I have made, but was looking for some experienced
> > opinions.
>
> I doubt you'll notice the difference in crank circle diameter unless
> the 170mm arms you've been using are detrimentally long for you
> (causing you to move some parts of your body other than your legs in
> order to perform your pedal stroke).
Thanks, first of all, to everyone for the opinions on this thread. It's
been...interesting.
> There is some threshold at which a crank becomes too long, for
> instance when one's knees hit one's chest while riding in the drops,
> or when the knee at the top of the pedal stroke begins to bind and
> resist further bending. Whatever this threshold, it is certain and
> identifiable for any given rider and bike.
>
> I postulate that the "best" crank length for any rider/bike
> combination is the longest one that gives no ill effects. However,
> it's clearly preferable to err on the short side of that length than
> to exceed it by even a little bit.
> IMO it's unlikely that even at 5'6" your legs are too short to pedal
> properly with 170mm cranks. You are, of course, the one who gets to
> make that judgement. But my advice to you is, if you think that 170mm
> cranks are actually too long for you, then why shorten them by only
> 2.5mm? Why not 165mm or even 155mm cranks? There's no point in
> almost addressing a suspected problem when you could be certain about
> it.
I actually don't have major mechanical problems with 170 mm cranks. At
most, I'm sure they're not the major thing keeping me from being faster
on the bike at the moment.
What has been bothering me is issues other than power. As I mentioned, I
have an achilles tendon issue. Of course, the standard solution is to
drop one's seat slightly, and work on cleat positioning. That's fine.
But I also have had serious knee issues in the past, long predating
cycling, and as you know, the proper solution for that is to raise the
seat.
I think the needs of these two conditions are not necessarily
overlapping. It doesn't bother me on short rides, so for now, I will do
nothing. But the third way that occurred to me was shrinking the crank
circle. With a smaller crank, I will get less knee AND ankle flex on
each stroke, which should help free me from my knee and ankle problems.
I'm going to keep tracking it for now, but we'll see.
> Legs vary in length by much more than the 8-9% difference between
> "very short" (165mm) and "very long" (180mm) crankarms. If your leg
> length is outside of the middle 10% of the overall range, it stands to
> reason that you might be better served by a crank that is shorter or
> longer than Shimano and Campagnolo supply.
My legs are not unusually short for my height. I can't remember all the
leg measurements I've done, but I wear a 30" pant leg.
Thanks,
--
Ryan Cousineau, rcou...@sfu.ca http://www.sfu.ca/~rcousine
President, Fabrizio Mazzoleni Fan Club
Patrick Lamb
<jbea...@lindsayhart.com> wrote:
>
> If you like them, try to work backwards
>towards a scientific justification using anecdotes and jargon extracted
>from the links provided in this thread. Use phrases like "finite element
>analysis." I don't know what it means, but it sounds persuasive. -- Jay
>Beattie.
I know what it means, but it makes me laugh when I see the term used
in the context of physiology.
Pat
Jon Isaacs
>ds=12183473&dopt=Abstract
>
>Andy Coggan
-----
To quote from the Abstract:
"A stepwise multiple linear regression procedure selected mechanical power
output, pedal speed, and pedal speed squared as the main determinants of
metabolic cost (R(2) = 0.99 +/- 0.01). Neither pedaling rate nor crank length
significantly contributed to the regression model. The cost of unloaded cycling
and delta efficiency were 150 metabolic watts and 24.7%, respectively, when
data from all crank lengths and pedal speeds were included in a regression.
Those values increased with increasing pedal speed and ranged from a low of 73
+/- 7 metabolic watts and 22.1 +/- 0.3% (145-mm cranks, 40 rpm) to a high of
297 +/- 23 metabolic watts and 26.6 +/- 0.7% (195-mm cranks, 100 rpm). These
results suggest that mechanical power output and pedal speed, a marker for
muscle shortening velocity, are the main determinants of metabolic cost during
submaximal cycling, whereas pedaling rate (i.e., activation-relaxation rate)
does not significantly contribute to metabolic cost."
--------
The way I read this is that the slower your pedal speed is for a given power
output, the more efficient you are, ie, a lower metabolic overhead.
Since one of the two effective ways to lower pedal speed is to shorten the
cranks, it does seem that shorter cranks and/or combined with taller gears are
indicated for TTs. Of course the third technique is to ride more slowly. I
normally employ all three techniques when I TT :-(
Comments, thoughts, misintepretations???
jon isaacs
Jay Beattie
"Patrick Lamb" <pdla...@comcast.net> wrote in message
news:pa2v5v8ogbphanu0q...@4ax.com...
I sort of know what it means, and actually, the term is used in the
context of physiology (or should I say pathology) to predict the effect
of certain forces on the human body. The models are derived from
crashing and squashing cadavers. NHTSA is big into this. Crushing
skulls with blunt objects is not my idea of having fun -- although I
have crushed a few beer cans against my blunt skull. -- Jay Beattie.
Russell
> My personal view on crank length is that one is free to choose what seems best
> because it really does not matter.
Ah yes, "size doesn't matter." :D
Russell
Patrick Lamb
OK, I can accept that. What makes me laugh is when I see FEM applied to
biomechanical questions, usually with enough assumptions to invalidate
any results. You know, the "assume the knee is friction-free and
neglect any muscular inefficiencies" kind of thing. I always want to
respond, "Assume a spherical cow."
Pat
--
Apologies to those easily confused. Address is spam-resistant.
Correct email address like pdlamb 'round-about comcast point net.
Eric
The road bike feels like a pedal car in comparison. However, it
sometimes is a little easier to spin on the road bike. The tourer is a
little harder to keep a 90 cadence, only because there is more
distance covered per rev, I guess (The tourer is geared like an MTB,
so I know that the gearing is not the issue).
E
"Jay Beattie" <jbea...@lindsayhart.com> wrote in message news:<v5tjopd...@corp.supernews.com>...
Bruce Dickson
> The way I read this is that the slower your pedal speed is for a given power
> output, the more efficient you are, ie, a lower metabolic overhead.
>
> Since one of the two effective ways to lower pedal speed is to shorten the
> cranks, it does seem that shorter cranks and/or combined with taller gears are
> indicated for TTs. Of course the third technique is to ride more slowly. I
> normally employ all three techniques when I TT :-(
Ha ha, yes but maybe there is more to it and you could go faster
otherwise everyone should be riding 145mm cranks at 40 rpm because
that is the most "efficient". As far as cadence goes there has been
research which shows that while theoretically it might be more
efficient to pedal a big gear at 40rpm most people pedal at around
90rpm and really this is the most efficient.
Check these out:-
http://www.slowtwitch.com/cgi-bin/parse.pl?file=../web/mainheadings/coachcorn/neuro.html&text
http://spokepost.com/news/?articleID=122
http://www.bsn.com/Cycling/articles/cadence.html
They all refer to another article:-
Ahlquist, L.E., et al. (1992) The effect of pedaling frequency on
glycogen depletion rates in type I and type II quadriceps muscle
fibers during sub-maximal exercise. Eur. J. Appl. Physiol. 65:360-4
I'm not sure if this is on the web but here is a snip from the
slowtwitch article which sums it up well:-
Just what is the difference between aerobic and neuromuscular fatigue?
My best explanation as a lay writer is that aerobic fatigue is more
systemic, and is more reliant on the oxygen end of the equation.
Neuromuscular fatigue is local—that is, it occurs in very specific
muscle groups, not throughout your body. Furthermore, it can be
specific to a part of a muscle. It's not related to oxygen debt, the
problem is the hyper-utilization of electrolytes and/or glycogen.
This was well demonstrated, I think, by Ahlquist, et al, in "The
effect of pedaling frequency on glycogen depletion rates in type I and
type II quadriceps muscle fibers during submaximal cycling exercise."
(European Journal of Applied Physiology, 1992:65). He demonstrated
that a trained group of cyclists would put out the same power with the
same aerobic cost—same oxygen consumption—whether pedaling at 50rpm or
100rpm. Blood lactate levels remained the same. You'd think there was
no difference in economy between these two cadences. What was found,
though, was that the quadracep glycogen depletion was significantly
greater at the lower cadence, and furthermore that this depletion
occurred only in the fast twitch muscle fibers. In other words, even
though we, as endurance athletes, might be predisposed to having a
greater degree of slow twitch muscle fibers, we will still recruit and
utilize our fast twitch muscles when the power requirement increases.
That's exactly what happens when the cadence decreases. The peak
torque during each revolution of the pedal stroke increases, and this
causes increased recruitment of our fast twitch fibers, which are less
able to burn fat, and which utilize glycogen at a higher rate. So,
while your heart rate will not increase with the use of a lower
cadence, you'll get more tired in the long run, and I mean that
literally: you'll suffer during the long run after you've depleted
your muscles during the long ride.
(end snip)
I think if someone researched it they would find the same thing with
crank length. That with longer cranks the torque required is less so
you will not fatigue as quickly. Otherwise we may as well all go out
and get some 145mm cranks for our single speed bikes put on a 86/11
gear and pedal along at 40rpm because the "research" says that is the
most efficient. Jan Ullrich would be pleased.
Bruce Dickson