Crank Length Selection

Scotty said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length, shoe
size, riding style. Everyone put in their opinions if they wish.

Everyone seems to adapt to crank most have, but the larger the crank,
the more leverage: except you don't want to raise knee above level or
less than 90 degrees. Then you overwork your knee joint and calves. Of
course everyone's motion/reps are limited by their tendons
flexibility, since joints are the biggest constraint of all. 175mm
does fine with my 6' tall 32" inseam, but I have excellent flexibility
considering. Just don't bang a pedal on corners leaning too far. Your
pedal, seating, and bar fit will be closely correlated, but you start
with the crank length and move on from there to match other interface
fits per riding position. A very individualistic science continually
boot-strapped optimized on rythmic rotational positions, so not to
incurr repetitive trauma disroders common to your anatomical makeup
and riding routine. In a nutshell anyway. The better fit on crank
length, the more positions on handlbar and even seat will be allowable
which offers a range from motion efficiency to breathing efficiency to
optimize spinning cycles.

I was thinking that on a time trial that a rider might go with a longer
crank arm, or on a course where there is extreme hills. Some people on the
forum suggest you can do anything with sprokets that can be done with
changing out your cranks. Are you talking about going longer so you can get
more top end speed/power with higher gear ratio.
Also, seems to me that if you go with a longer crank then you achieve more
power verses your wattage-more power per watt, and a lower VO2 max, overall.
I have always kept the stock cranks on all my bikes, it has never been a big
deal, cause I have never raced. When I bought my last bike the guy that
fitted me said I have long legs. He never said to change out the 175mm for
anything higher or anything like that.
"Scotty" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length,
shoe size, riding style. Everyone put in their opinions if they wish.

Scotty said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length, shoe
size, riding style. Everyone put in their opinions if they wish.

Humans are more adaptable than you might at first imagine. While riders
at the extremes* have special needs/desires, most riders can ride 165 to
175 without complaint.

That said, riders often have strong preferences to cure both real and
imagined problems.

[*extremes obviously include small and large riders. Extremes also
include special events and machines. Generally longer for mud/climbing,
shorter for higher crank rpm. And converted low-BB fixie riders had
better check cornering clearance!]
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

On Sat, 17 Feb 2007 19:16:58 -0500, "Scotty" <[email hidden]>

Quoted message said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length, shoe
size, riding style. Everyone put in their opinions if they wish.

175mm

--
JT
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On Feb 17, 8:00 pm, John Forrest Tomlinson <[email hidden]>

Quoted message said:

On Sat, 17 Feb 2007 19:16:58 -0500, "Scotty" <[email hidden]>

Quoted message said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length, shoe
size, riding style. Everyone put in their opinions if they wish.

175mm

--
JT
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Quoted message said:

From these abstracts I get the idea it might not matter much, even as

short as 120 mm and as long as 220 mm.

Martin JC, Brown NA, Anderson FC, Spirduso WW. "A governing
relationship for repetitive muscular contraction." Department of
Exercise Science, School of Public Health, The University of South
Carolina, Columbia 29208, USA. [email hidden]

During repetitive contractions, muscular work has been shown to
exhibit complex relationships with muscle strain length, cycle
frequency, and muscle shortening velocity. Those complex relationships
make it difficult to predict muscular performance for any specific set
of movement parameters. We hypothesized that the relationship of
impulse with cyclic velocity (the product of shortening velocity and
cycle frequency) would be independent of strain length and that
impulse-cyclic velocity relationships for maximal cycling would be
similar to those of in situ muscle performing repetitive contraction.
Impulse and power were measured during maximal cycle ergometry with
five cycle-crank lengths (120-220mm). Kinematic data were recorded to
determine the relationship of pedal speed with joint angular velocity.
Previously reported in situ data for rat plantaris were used to
calculate values for impulse and cyclic velocity. Kinematic data
indicated that pedal speed was highly correlated with joint angular
velocity at the hip, knee, and ankle and was, therefore, considered a
valid indicator of muscle shortening velocity. Cycling impulse-cyclic
velocity relationships for each crank length were closely approximated
by a rectangular hyperbola. Data for all crank lengths were also
closely approximated by a single hyperbola, however, impulse produced
on the 120mm cranks differed significantly from that on all other
cranks. In situ impulse-cyclic velocity relationships exhibited
similar characteristics to those of cycling. The convergence of the
impulse-cyclic velocity relationships from most crank and strain
lengths suggests that impulse-cyclic velocity represents a governing
relationship for repetitive muscular contraction and thus a single
equation can predict muscle performance for a wide range of functional
activities. The similarity of characteristics exhibited by cycling and
in situ muscle suggests that cycling can serve as a window though
which to observe basic muscle function and that investigators can
examine similar questions with in vivo and in situ models.

Martin JC, Malina RM, Spirduso WW. "Effects of crank length on maximal
cycling power and optimal pedaling rate of boys aged 8-11 years."
Department of Exercise and Sport Science, University of Utah, Salt
Lake City 84112-0920, USA. [email hidden]

It is generally reported that cycle crank length affects maximal
cycling power of adults and that optimal crank length is related to
leg length. This suggests that the use of standard length cycle cranks
may provide nonoptimal test conditions for children. The purpose of
this study was to determine the effects of cycle-crank length on
maximal cycling power and optimal pedaling rate of 17 boys aged 8-11
years. The boys performed maximal cycle ergometry with standard (170
mm) cycle cranks and with a crank length that was 20% of estimated leg
length (LL20). Power produced when using the 170 mm cranks [mean
(SEM)] [364 (18) W] did not differ from that produced with the LL20
cranks [366 (19)]. Optimal pedaling rate was significantly greater for
the LL20 cranks [129 (4) rpm] than for the 170 mm cranks [114 (4)
rpm]. These data suggest that standard 170 mm cranks do not compromise
maximal power measurements in boys aged 8-11 years

Martin JC, Spirduso WW. "Determinants of maximal cycling power: crank
length, pedaling rate and pedal speed." University of Utah, Department
of Exercise and Sport Science, 250S. 1850E. Rm. 200, Salt Lake City,
UT 84112-0920, USA. [email hidden]

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.

McDaniel J, Durstine JL, Hand GA, Martin JC. "Determinants of
metabolic cost during submaximal cycling." Department of Exercise
Science, University of South Carolina, Columbia, South Carolina 29208,
USA.

The metabolic cost of producing submaximal cycling power has been
reported to vary with pedaling rate. Pedaling rate, however, governs
two physiological phenomena known to influence metabolic cost and
efficiency: muscle shortening velocity and the frequency of muscle
activation and relaxation. The purpose of this investigation was to
determine the relative influence of those two phenomena on metabolic
cost during submaximal cycling. Nine trained male cyclists performed
submaximal cycling at power outputs intended to elicit 30, 60, and 90%
of their individual lactate threshold at four pedaling rates (40, 60,
80, 100 rpm) with three different crank lengths (145, 170, and 195
mm). The combination of four pedaling rates and three crank lengths
produced 12 pedal speeds ranging from 0.61 to 2.04 m/s. Metabolic cost
was determined by indirect calorimetery, and power output and pedaling
rate were recorded. 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.

"Scotty" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length,

shoe

Quoted message said:

size, riding style. Everyone put in their opinions if they wish.

In general better quality cranks come in 2.5mm length increments from
165mm to 180mm long with 170mm being the standard crank length for most
road bikes.

A lot of track bikes use 165mm cranks for ground clearance and many MTBs
came with 180mm cranks for climbing.

I was in a conversation today with someone who rides 177.5mm cranks. He
claimed that he had problems with 175mm and 180mm cranks and he could tell
the difference.

Take a look at a ruler or scale:

2.5mm is .098" or less than 1/8"
5mm is .197 which is slightly more than 3/16"
10mm is .394" or slightly more than 3/8"

A 2.5mm or 5mm change doesn't seem very significant compared to the length
of your legs and feet but some people are probably sensitive enough to
feel a 2.5mm difference.

I have 5 road bikes. Several have 175mm cranks and I can't tell any
difference when I switch back and forth between them and my bikes with
170mm cranks . Some time ago I experimented with 180mm cranks for
climbing. I could feel a difference over 170mm cranks but not 175mm.

Last summer I changed out the 180mm cranks on my old MTB for a more modern
175mm crankset. I can't tell any difference.

Chas.

* * Chas said:

Last summer I changed out the 180mm cranks on my old MTB for a more modern
175mm crankset. I can't tell any difference.

A bike I used to ride was equipped with an unmatched pair, 175 on one
side and 172.5 on the other one. I realized it was so just by chance,
after a couple of years.

Sergio
Pisa

sergio said:

* * Chas said:

Last summer I changed out the 180mm cranks on my old MTB for a more modern
175mm crankset. I can't tell any difference.

A bike I used to ride was equipped with an unmatched pair, 175 on one
side and 172.5 on the other one. I realized it was so just by chance,
after a couple of years.

Sergio
Pisa

Sergio,

If your right side was longer and left leg was stronger, that may have
been a custom balanced crank fit if you never noticed with 3/32"
longer crank on weak side. Otherwise, you were optimizing power from
your strong leg while building your weaker side up from reduced
leverage. My legs are real strong though so might be insignificant
either way for myself or you since didn't notice empirically. Either
way it may be balanced forces or help balance strength training either
way, or it is negligible. Psychologically may be the greatest
ehhancement/detraction unless a constraint of too tall or too short;
or in effect less than 90 degree knee bend or can't touch the pedals
without rupturing yourself (assuming you have a 'normal' crotched seat
- ouch!). I really do feel your pain if you have a crotched seat guys!

* * Chas said:

"Scotty" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length,

shoe

Quoted message said:

size, riding style. Everyone put in their opinions if they wish.

In general better quality cranks come in 2.5mm length increments from
165mm to 180mm long with 170mm being the standard crank length for most
road bikes.

A lot of track bikes use 165mm cranks for ground clearance and many MTBs
came with 180mm cranks for climbing.

I was in a conversation today with someone who rides 177.5mm cranks. He
claimed that he had problems with 175mm and 180mm cranks and he could tell
the difference.

Take a look at a ruler or scale:

2.5mm is .098" or less than 1/8"
5mm is .197 which is slightly more than 3/16"
10mm is .394" or slightly more than 3/8"

A 2.5mm or 5mm change doesn't seem very significant compared to the length
of your legs and feet but some people are probably sensitive enough to
feel a 2.5mm difference.

I have 5 road bikes. Several have 175mm cranks and I can't tell any
difference when I switch back and forth between them and my bikes with
170mm cranks . Some time ago I experimented with 180mm cranks for
climbing. I could feel a difference over 170mm cranks but not 175mm.

Last summer I changed out the 180mm cranks on my old MTB for a more modern
175mm crankset. I can't tell any difference.

I ride 175s. If you put on 177.5, and didn't raise the saddle, I'd
notice. If you raised the saddle 2.5mm probably wouldn't notice when
I started pedalling, but think I might notice over time that I was
feeling some joint strain at the bottom of the stroke. Maybe.

2.5 mm shorter cranks I probably wouldn't notice at all.

--
JT
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ddog said:

sergio said:

* * Chas said:

Last summer I changed out the 180mm cranks on my old MTB for a more modern
175mm crankset. I can't tell any difference.

A bike I used to ride was equipped with an unmatched pair, 175 on one
side and 172.5 on the other one. I realized it was so just by chance,
after a couple of years.

Sergio
Pisa

Sergio,

If your right side was longer and left leg was stronger, that may have
been a custom balanced crank fit if you never noticed with 3/32"
longer crank on weak side. Otherwise, you were optimizing power from
your strong leg while building your weaker side up from reduced
leverage. My legs are real strong though so might be insignificant
either way for myself or you since didn't notice empirically. Either
way it may be balanced forces or help balance strength training either
way, or it is negligible. Psychologically may be the greatest
ehhancement/detraction unless a constraint of too tall or too short;
or in effect less than 90 degree knee bend or can't touch the pedals
without rupturing yourself (assuming you have a 'normal' crotched seat
- ouch!). I really do feel your pain if you have a crotched seat guys!

It's 2.5 mm difference for Gods sake. Two different socks have the same
effect.

Lou
--
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Scotty said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length, shoe
size, riding style. Everyone put in their opinions if they wish.

Theory is right. Put 3 people in a room and ask about crank length and
get 4 answers. NO rules, use what works for you.

Scotty said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length, shoe
size, riding style. Everyone put in their opinions if they wish.

It really, really does not matter all that much. I have followed
traditional wisdom for someone my size (5'11", basically a 56-cm bike),
in using 170mm cranks for the road, 165 for track/fixed gear, and 175
for mountain. But I have also swapped things around on occasion, and
found little difference. Maybe I can spin a bit faster with the shorter
cranks on the fixed gear, but maybe I spin faster because I have to,
especially going downhill.

don't worry about it. The only important thing about cranks is to avoid
silly colors.

--

David L. Johnson

"What am I on? I'm on my bike, six hours a day, busting my ass. What
are you on?" --Lance Armstrong

A Muzi said:

[*extremes obviously include small and large riders. Extremes also
include special events and machines. Generally longer for mud/climbing,
shorter for higher crank rpm. And converted low-BB fixie riders had
better check cornering clearance!]

The last concern is overblown. Very few such conversions have less than
a 45-degree lean angle before the pedal contacts the road, and if you
are leaning over more than that you are on the way down, anyway. Lots
of people experience hitting a pedal and going down in a corner, but
wrongly infer that the pedal strike caused the fall. Usually it's the
other way around.

--

David L. Johnson

Anyone who is capable of getting themselves made President should on
no account be allowed to do the job. -- Douglas Adams

"David L. Johnson" <[email hidden]> schreef in bericht
news:[email hidden]...

Quoted message said:

A Muzi said:

[*extremes obviously include small and large riders. Extremes also
include special events and machines. Generally longer for mud/climbing,
shorter for higher crank rpm. And converted low-BB fixie riders had
better check cornering clearance!]

The last concern is overblown. Very few such conversions have less than a
45-degree lean angle before the pedal contacts the road, and if you are
leaning over more than that you are on the way down, anyway. Lots of
people experience hitting a pedal and going down in a corner, but wrongly
infer that the pedal strike caused the fall. Usually it's the other way
around.

--

David L. Johnson

Two times now my pedal contacted the road because i didn't stop pedaling in
a steep corner.
I didn't fall, my rear wheel was shortly lifted from the ground and then put
down again a little bit further aside.
Strange experience, 180mm cranks, look pedals, great skidding surface ;-)

Taeke

Quoted message said:

Anyone who is capable of getting themselves made President should on
no account be allowed to do the job. -- Douglas Adams

Lou Holtman said:

It's 2.5 mm difference for Gods sake. Two different socks have the same
effect.

Lou

If God's sake does not include leverage, turning limits, and
biomechanical equilibrium, in a narrow minded overly simplistic
viewpoint you may be right. But because there are always limits that
effect different people differently, overly simplistic one liners are
always wrong and can hurt some people if they weigh your comments as
legitimate arguments.

Quoted message said:

ddog said:

sergio said:

On 18 Feb, 06:05, "* * Chas" <[email hidden]> wrote:

> Last summer I changed out the 180mm cranks on my old MTB for a more
> modern
> 175mm crankset. I can't tell any difference.
A bike I used to ride was equipped with an unmatched pair, 175 on one
side and 172.5 on the other one. I realized it was so just by chance,
after a couple of years.

Sergio
Pisa

Sergio,

If your right side was longer and left leg was stronger, that may have
been a custom balanced crank fit if you never noticed with 3/32"
longer crank on weak side. Otherwise, you were optimizing power from
your strong leg while building your weaker side up from reduced
leverage. My legs are real strong though so might be insignificant
either way for myself or you since didn't notice empirically. Either
way it may be balanced forces or help balance strength training either
way, or it is negligible. Psychologically may be the greatest
ehhancement/detraction unless a constraint of too tall or too short;
or in effect less than 90 degree knee bend or can't touch the pedals
without rupturing yourself (assuming you have a 'normal' crotched seat
- ouch!). I really do feel your pain if you have a crotched seat guys!

It's 2.5 mm difference for Gods sake. Two different socks have the same
effect.

Lou

The thickness of your socks will ot influence the effective length of
your cranks, but I agree, what in godsname we're talking about!?

Martin

--
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ddog said:

Lou Holtman said:

It's 2.5 mm difference for Gods sake. Two different socks have the same
effect.

Lou

If God's sake does not include leverage, turning limits, and
biomechanical equilibrium, in a narrow minded overly simplistic
viewpoint you may be right. But because there are always limits that
effect different people differently, overly simplistic one liners are
always wrong and can hurt some people if they weigh your comments as
legitimate arguments.

Ok I challenge you if you could feel the difference if someone changed
one of your cranks with a 2.5 mm shorter one without telling you. My
guess is you don't and you don't get hurt either. Just my 2 cents.

Lou, 170, 172.5 and 175 mm cranks on his bikes.
--
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Lou Holtman said:

Ok I challenge you if you could feel the difference if someone changed
one of your cranks with a 2.5 mm shorter one without telling you. My
guess is you don't and you don't get hurt either. Just my 2 cents.

Lou, 170, 172.5 and 175 mm cranks on his bikes.

Lou,

Because you feel no difference, are you inferring that NO ONE should
either and have your exact anatomical parameters? Not only is this
unwittingly bold to suggest 'nothing matters' or has critical and
specific biomechanical bounds (for example, there will be some 2.5mm
difference that will effect EVERYONE, just different limits), but to
propose it in a format that it is 'Gods sake' and you are his
interpretor is beyond 'just your 2 cents'.

Your 'guess' that it doesn't effect me may be right, but is definitely
wrong that it will not effect EVERYONE else. So your challenge is
meaningless since the subject was intended for all parties, not ME
specifically. The logical challenge would be towards you to find out
all the differences of a wider population of people that it WOULD
make a difference. I have studied the differences in over a dozen
micromotion disciplines and in exhaustive depth, so I have learned
those lessons; and I take the wide Safety differences between
different people seriously. Anything highly repetitive can be a major
concern, so incremental differences should be respected logically
since RTD's are FOREVER once you incurr them ONCE.

ddog said:

Lou Holtman said:

Ok I challenge you if you could feel the difference if someone changed
one of your cranks with a 2.5 mm shorter one without telling you. My
guess is you don't and you don't get hurt either. Just my 2 cents.

Lou, 170, 172.5 and 175 mm cranks on his bikes.

Lou,

Because you feel no difference, are you inferring that NO ONE should
either and have your exact anatomical parameters? Not only is this
unwittingly bold to suggest 'nothing matters' or has critical and
specific biomechanical bounds (for example, there will be some 2.5mm
difference that will effect EVERYONE, just different limits), but to
propose it in a format that it is 'Gods sake' and you are his
interpretor is beyond 'just your 2 cents'.

How can anybody find out scientific that a 2.5 mm change in cranklength
make a difference? Do the people who say they can
feel that difference also adjust there saddle height every time they
wear different shorts with different paddings or different shoes? I
think there is an upper and a lower limit (there has to be) and I am
convinced that for most people 2.5 mm is within those limits.

Lou
--
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