Significance of crank arm length?

[Billx]

How much of an impact on performance does crank arm length have? My current 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" <[email protected]> wrote in message news:[email protected]...
> How much of an impact on performance does crank arm length have? My
current
> 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?
>
>No. Normally you probably would have had 172.5mm, but the difference in
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 Ca]

BillX-<< How much of an impact on performance does crank arm length have?

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]

In article <[email protected]>,
"Hjalmar Duklæt" <[email protected]> wrote:

> "BillX" <[email protected]> wrote in message news:[email protected]...
> > How much of an impact on performance does crank arm length have? My
> current
> > 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?
> >
> >No. Normally you probably would have had 172.5mm, but the difference in
> 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

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, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club

 

[Billx]

I'm not having problems with my 170mm cranks but am looking at buying 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.

>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"

 

[Wayne T]

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.

"Qui si parla Campagnolo" <[email protected]> wrote in message
news:[email protected]...
> BillX-<< How much of an impact on performance does crank arm length have?
>
> 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"

 

[Bluto]

Ryan Cousineau <[email protected]> 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).

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

 

[Harris]

Wayne T <[email protected]> wrote:
> 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.

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 \"Ro]

Some where out there is an equation for crank length based on leg length, can't 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:

> How much of an impact on performance does crank arm length have? My current 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?

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[Wayne T]

"Bruce Dickson" <[email protected]> wrote in message
news:[email protected]...
> The only study I know of on crank length was this one:-
>
>
http://link.springer-ny.com/link/service/journals/00421/contents/01/00400/in dex.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.

What is your Inseam?

>
> Bruce Dickson

 

[One Of The Six]

<[email protected]> wrote in message news:[email protected]...
> NeauDL neaudl writes:
>
> > I switched from 172.5 to 170 mm cranks (height 5'6") a year ago and my patellar 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 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.
>

Since I have the exact same experience I guess the rumor pot gets another tale.

 

[Peter Cole]

"Bluto" <[email protected]> wrote in message
news:[email protected]...
> [email protected] (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

 

[Calvin]

This is of interest to me, as I would suspect of interet to anyone who 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" <[email protected]> wrote in message
news:<[email protected]>...
> "Bruce Dickson" <[email protected]> wrote in message
> news:[email protected]...
> > The only study I know of on crank length was this one:-
> >
> >
> http://link.springer-ny.com/link/service/journals/00421/contents/01/00400/in dex.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.
>
> What is your Inseam?
>
> >
> > Bruce Dickson

 

[Jay Beattie]

"Wayne T" <[email protected]> wrote in message
news:[email protected]...
> 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.

 

[Ryan Cousineau]

In article <[email protected]>, [email protected] (Bluto) wrote:

> Ryan Cousineau <[email protected]> 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, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club

 

[Patrick Lamb]

On Thu, 27 Feb 2003 18:53:13 -0800, "Jay Beattie" <[email protected]> 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

 

[Jay Beattie]

"Patrick Lamb" <[email protected]> wrote in message
newsa2v5v8ogbphanu[email protected]...
> On Thu, 27 Feb 2003 18:53:13 -0800, "Jay Beattie" <[email protected]> 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.

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.

 

[Patrick Lamb]

Jay Beattie wrote:
> "Patrick Lamb" <[email protected]> wrote in message
> news[email protected]...
>
>>On Thu, 27 Feb 2003 18:53:13 -0800, "Jay Beattie" <[email protected]> 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.
>
>
> 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.

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]

I agree with you. On my road bike, I have 170mm, on the tourer, 175mm. 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" <[email protected]> wrote in message
news:<[email protected]>...
> "Wayne T" <[email protected]> wrote in message
> news:[email protected]...
> > 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.

 

[Harrow]

Originally posted by Billx
How much of an impact on performance does crank arm length have? My current 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?

Bill X,

I have 172.5mm Shimano 105 with Octalink. If you live in Sydney, I would consider swapping if you have the same type because I am a lot shorter than 6 ft, and would like to slightly reduce my vertical leg travel distance.

Regards,
Harrow.