# Crank Arm Length



## 2faced (Apr 18, 2004)

Is there a noticeable difference in performance/spin/power transfer with regard to crank arm length? What are some factors I should consider in deciding which 170/172.5/175 is correct for me? Can a professional bike fit identify the ideal length or is it a rider preference issue? I'm about ready to fork out some hard earned cash for a new bike and I want EVERYTHING perfect.


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## Kerry Irons (Feb 25, 2002)

*Do what you like*

The "logic" of "crank length should be proportional to leg measurements" has been around for a LONG time, and lots of people have turned that "logic" into a formula for determining crank length. Only one problem: the research doesn't support it. Don't you just hate it when the data doesn't support the theory? One key feature that is often ignored in these discussions is the duration of muscle contraction that is controlled by cadence. It just may be that there is an optimum here, which is why there is a fairly narrow range of cadence for optimum performance. Longer cranks mean lower cadence, moving you out of that optimum range. Crank length has been a point of debate since the introduction of the "safety" bicycle in the late 1800s, and there have been all sorts of fads in that regard. Do you think that we have standardized on this narrow range because of some sort of global conspiracy, or because well over 100 years of experience (and testing the limits) have repeated shown that the 170-180 mm is really what works for human beings?

There is no reliable formula for predicting crank length. There ARE lots of formulas out there, but they are just figments of the imagination of their purveyors. No one has ever done a study that shows how crank length should relate to anything. Probably the best work done on this VERY difficult to research topic was by Lennard Zinn. He unintentionally showed how our adaptability was more important than our size or riding style. He's sure that the results of his study are wrong, but he just can't seem to find any data to support his pre-conceptions.

You will find no high quality data to support any particular crank length as being better than any other. This is true whether or not you correct for leg length, femur length, etc. On the other hand, you will find lots of anecdotal or low quality data to support all kinds of conclusions, and more theories than you can shake a stick at. A rider's response to changes in crank length is 1) highly individual, 2) dependent on riding style and the event (TT, climbing, crits, track racing, etc.), and 3) most important, highly adaptive. This is why it is so hard to study the effect of crank length.

It is generally the case that longer cranks make it harder to spin, and high cadence is the best way to minimize knee problems. That said, an extra 5 mm in crank length may only take away 3-5 rpm of spin, so it is not a large effect. Spinning is more physiologically efficient, all else equal.


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## MR_GRUMPY (Aug 21, 2002)

If you're 5' 08" or above, get 175's
If you're 5' 2" get 172.5's
175's may slow your spin for two or three weeks, until your body gets used to them.
What size cranks do you have now ? How tall are you ? What type of riding do you do ?
The only major mistake you could make, would be to buy 175's if you are 5' 0".
There are many people who can "spin" a 180 crank.


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## XCGEEK (Jan 23, 2002)

*2 points*

First, if you have more than one bike make sure all of your bikes have the same length cranks. I've never heard of any research backing me up, so I may be talking out of my a$$, but I can notice a difference. When I put the same length cranks on my road, TT, cx,and mtb bikes I was definitly more comforatable on all of them.

Second, and again this is my observations, I think crank length should be based on femur length. It just seems to make sense to me. I have long femurs for my height (5'9") and I like longish (175) cranks on all my bikes for my height. It seems easier to set up my cleats in the right position and I can climb the steep stuff better. According to my SRM, more watts in the saddle at the same given HR. Who knowes?

Justin


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## fiddledoc (May 28, 2003)

*huh?*



MR_GRUMPY said:


> If you're 5' 08" or above, get 175's
> If you're 5' 2" get 172.5's
> 175's may slow your spin for two or three weeks, until your body gets used to them.
> What size cranks do you have now ? How tall are you ? What type of riding do you do ?
> ...


Here's a rhetorical question: From where did you pull these figures?

I'm 5''7", and after using a 170 crank, put on a 172.5. After 9 months, I can still feel the difference, and they feel too large to me. If I buy a new crank, I'll go back to 170. It's not math--it's feel. Either it's comfortable or it's not.


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## srf (Jun 28, 2004)

IMHO it has a lot to do with what you're comfortable with. Without trying them out, I don't know that you'll ever know. I'm 5'10" and have one bike with 175mm and one with 172.5mm. I've never been able to come to terms with the 175mm and will probably move that bike to 172.5mm. It probably has a lot more to do with if you prefer lower or higher RPMs (I prefer slightly higher). Supposedly longer cranks help you on hills, though that doesn't seem to hold true for me.


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## TurboTurtle (Feb 4, 2004)

2faced said:


> Is there a noticeable difference in performance/spin/power transfer with regard to crank arm length? What are some factors I should consider in deciding which 170/172.5/175 is correct for me? Can a professional bike fit identify the ideal length or is it a rider preference issue? I'm about ready to fork out some hard earned cash for a new bike and I want EVERYTHING perfect.


I have everything from 165 to 175mm and cannot tell the difference. Any blind testing (even from those who KNOW it has to be) that I have seen has been zero difference. - TF


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## tampafw (Jul 25, 2009)

2faced said:


> Is there a noticeable difference in performance/spin/power transfer with regard to crank arm length? What are some factors I should consider in deciding which 170/172.5/175 is correct for me? Can a professional bike fit identify the ideal length or is it a rider preference issue? I'm about ready to fork out some hard earned cash for a new bike and I want EVERYTHING perfect.


I think in all honestly it's a very personal and individual decision, there is no right or perfect number. I'm 6'0 even barefoot and I am on the other end of the spectrum with sizing. For what it's worth, my 40K PR is 56:08 and that was done on 170's, but I digress that was 16 years ago....I'm so old!

Now that I'm recently back into the sport I am trying out some 172.5's and while I don't have a good starting point reference with my layoff, I can say I have yet to get comfortable. I may very well go back to 170's and much of the conventional wisdom says I should go UP to 175's. My knees won't take the added stress I know for sure, but I cannot turn 'circles' as well with 172.5's and fight turning 'squares'. I know how to pedal a ring properly and I'm struggling to get the old feel back with the 172.5's. 

It's personal......and with a 34.25" inseam I go against conventional wisdom.


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## SystemShock (Jun 14, 2008)

I'm 5'10", but have the leg length of your average 5'8" person.

I've tried 175s... they were too long for me.
172.5s? Ahhhh. Just right. :thumbsup:
.


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## chas0039 (Jun 26, 2007)

I am 6"2" with a 33" inseam and I have 5 bikes, 3 with 172 and 2 with 175 and I ride them all interchangeably (no racing). Compatibility is really a personal thing and from what I have read, this specification is one of the least critical as far as proper bike fitting goes.


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## tampafw (Jul 25, 2009)

chas0039 said:


> I am 6"2" with a 33" inseam and I have 5 bikes, 3 with 172 and 2 with 175 and I ride them all interchangeably (no racing). Compatibility is really a personal thing and from what I have read, this specification is one of the least critical as far as proper bike fitting goes.


Isn't that weird with body vatiation? You are an inch taller than me, but my inseam is 1.25 longer? Thus keeping bike fitters eternally busy....


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## olr1 (Apr 2, 2005)

Some people insist crank length is important; I'm 5'8", and use 175s on the mountain bike, 170s on one road bike and 172.5s on the other road bike and never think twice about any of them.

One of my acquaintances used a 170 left crank with a 175 right crank and didn't notice for a year....


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## Britishbane (Mar 4, 2009)

not to hijack...but, I'm 6'7'', does that mean I should use 180mm cranks?


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## Kerry Irons (Feb 25, 2002)

*Your length*



Britishbane said:


> not to hijack...but, I'm 6'7'', does that mean I should use 180mm cranks?


No. Crank length is personal, and there is no way to predict the "right" length for you. If you like to spin, use shorter cranks, If you like to push, use longer. Shorter is better for your knees, but not an issue if your knees are OK.


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## WizardTim (Aug 4, 2009)

I'm 5'9" with 32" inseam. Got 170s on the "fair weather" bike and 172.5s on the "going somewhere where it might get stolen" bike. Can't tell the difference really. Maybe I should ride more...


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## Britishbane (Mar 4, 2009)

Thanks for the response Kerry. I do like to spin ( I think?). My preferred cadence hovers around 100rpm or so. 

Helpful thread guys/gals.


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## SystemShock (Jun 14, 2008)

Britishbane said:


> not to hijack...but, I'm 6'7'', does that mean I should use 180mm cranks?


At your height/probable leg length, I strongly suspect you should at least _try_ some 180s.
.


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## satanas (Nov 8, 2002)

I think Kerry nailed it in his first post. The later responses run the gamut from "cannot tell any difference and don't care" to people having very precise preferences. I've observed a similar range of responses amongst my acquaintances. 

FWIW, I'm 180cm tall, and have slightly shorter lower legs than average, otherwise I'd be a few cm taller. I've tried 165, 170, 172.5, 175, 178 and 180mm cranks, and could tolerate all except the 165 and 180mm. The 178mm cranks were only used for a short (1 hour), mostly uphill MTB ride and were (for me) great for climbing but wretched on the flat. I now use 172.5mm cranks for all except the fixed which has 170mm as these are less inclined to tear my legs off on fast descents. Sadly, I suspect I may be forced to revert to 175mm when I buy another MTB, as the only cranks available in a range of lengths seem to be XTR, which has an unacceptably high Q factor - for me. I find 172.5mm and low Q to be more comfortable, even for offroad use.

Unfortunately, the only way to figure out what crank length is best for you is to try a variety; this is easier if you work in the industry!


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## davidka (Dec 12, 2001)

The best thing regarding crank length I've heard is your optimum crank length is probably the one you've ridden the most. That said, if you're 6'7" and 175's feel better than 180's, you should probably ride the 180's and really give them a chance (the SRAM Rival crank is a reasonably priced crank available in 180mm). I'm 6'4" and I ride 180's. I rode 175's for several years and when I tried 180's, they felt better from the 1st pedal stroke.


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## JaeP (Mar 12, 2002)

I'm 6'2" with a 36" inseam (LeMond method) and I switched all my bikes to 180mm cranks (well, the RB-2 has 177.5). I am not, nor will I ever be, a spinner. I don't have the desire nor the discipline to be a racer, but I do like to ride.

If it feels good, that can't be bad.


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## Ronman (Feb 12, 2007)

I'm 6'5" with a 36" inseam. I've ridden 172.5, 175 and currently ride 177.5 crank arms. I never did get comfortable on the 172.5 arms. They just felt too tight in the rotational circle. Between the 175 and 177.5 arms I honestly don't feel much difference in climbing or ability to spin. I settled on 177.5 since they don't seem to impede my ability to spin, and I figure the additional leverage couldn't hurt when climbing. My cadence averages around 90 on the flats.


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## Salsa_Lover (Jul 6, 2008)

SystemShock said:


> I'm 5'10", but have the leg length of your average 5'8" person.
> 
> I've tried 175s... they were too long for me.
> 172.5s? Ahhhh. Just right. :thumbsup:
> .


same here 5' 11" longer torso shorter legs, I use a 172.5, the 175 and thr 170 feel wrong to me


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## tsull247 (May 8, 2008)

172.5mm=6.692in
170mm=6.629in
difference.063in = 1/16 of an inch

preception vs. reality


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## SystemShock (Jun 14, 2008)

tsull247 said:


> 172.5mm=6.692in
> 170mm=6.629in
> difference.063in = 1/16 of an inch
> 
> preception vs. reality


Actually, every 2.5mm difference in crank arm length = a 16mm difference in the size of the pedaling circle.

Some ppl may not be able to feel the diff, but I was certainly able to. 
175s felt big, and were hard to spin.
172.5s were a nice blend of spin and leverage.

But I agree that ymmv.
.


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## martinrjensen (Sep 23, 2007)

Huh? How's that? I can see that a 1/16 inch difference in crank arm length might equal a 1/8" (or double) diffence in overall crank length but I don't get 16 mm. 
Are you saying that the 1/16" longer crank gives a 16mm pedal circumference? I don't understand how pedal circumference would be relevant here. I'm thinking that only the minimum and maximum would matter


SystemShock said:


> Actually, every 2.5mm difference in crank arm length = a 16mm difference in the size of the pedaling circle.
> .


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## tsull247 (May 8, 2008)

The difference in circumferense 170mm to 172mm is 7.85mm equal to .31 inches added to the distance around the crcle.


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## martinrjensen (Sep 23, 2007)

ya better say "across" the circle. The circumference as SystemShock says, is about 16 inches. My thinking is that only the diameter is important and as you are pointing out, .31 inch aint much.


tsull247 said:


> The difference in circumferense 170mm to 172mm is 7.85mm equal to .31 inches added to the distance around the crcle.


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## wim (Feb 28, 2005)

martinrjensen said:


> ya better say "across" the circle. The circumference as SystemShock says, is about 16 inches. My thinking is that only the diameter is important and as you are pointing out, .31 inch aint much.


Pedal circle circumference is not "about 16 inches." SystemShock stated correctly that the _difference_ in pedal circle circumference between a 170.0 mm and a 172.5 mm crank is about 16 mm. If the numbers interest you, here they are. Circumference = pi x diameter:

170.0 radius x 2 = 340.0 mm diameter = 1,067.5 mm circumference
172.5 radius x 2 = 345.0 mm diameter = 1,083.3 mm circumference
Difference in circumference = 15.8 mm. 

Circumference matters. In very simplified terms, power is work over time (P = W/t). That makes circumference important—it's how far your pedal has to travel in a given time. At the _same leg speed_, you'll need more time to complete a 172.5 mm pedal circle than a 170.0 mm pedal circle. Conversely, to keep the _same cadence_ with both cranks, you need to increase your leg speed with the longer crank. Because some people find that difficult, you often hear that "shorter cranks are easier to spin."


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## martinrjensen (Sep 23, 2007)

*my mistake*

My mistake, opps


wim said:


> Pedal circle circumference is not "about 16 inches." SystemShock stated correctly that the _difference_ in pedal circle circumference between a 170.0 mm and a 172.5 mm crank is about 16 mm. If the numbers interest you, here they are. Circumference = pi x diameter:
> 
> 170.0 radius x 2 = 340.0 mm diameter = 1,067.5 mm circumference
> 172.5 radius x 2 = 345.0 mm diameter = 1,083.3 mm circumference
> ...


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## SystemShock (Jun 14, 2008)

martinrjensen said:


> Huh? How's that? I can see that a 1/16 inch difference in crank arm length might equal a 1/8" (or double) diffence in overall crank length but I don't get 16 mm.
> Are you saying that the 1/16" longer crank gives a 16mm pedal circumference? I don't understand how pedal circumference would be relevant here. I'm thinking that only the minimum and maximum would matter


We're not talking 'pedal circumference'. I'm sure pedals are fine whether fat or thin. We're talking pedaling circle.

The crankarm length is just the radius. The pedaling circle is 2 x the radius x the value of pi.












*edit–* Wim caught it. Thanks Wim. :thumbsup:
.


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## SystemShock (Jun 14, 2008)

tsull247 said:


> The difference in circumferense 170mm to 172mm is 7.85mm equal to .31 inches added to the distance around the crcle.


I'm not sure how you came to that, but that would be incorrect.

Again, 2 x the radius [aka crankarm length diff] x the value of pi.
.


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## heathb (Nov 1, 2008)

I've had all the DA7800 cranks from 170 to 185, I put about 10,000 miles on a set of 175, but I found that I didn't like the longer cranks and I started to really like the shorter cranks overtime.

Been riding the 170 for the whole season, I'm a spinner with my average around 100-110. 

The thing I noticed was a lot less cramping issues with the shorter cranks. When I was riding the 177.5 and larger I was having hellish cramping at the end of the day.

I'm 6'2" with a 34in inseam.


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## Stogaguy (Feb 11, 2006)

*Welcome to middle age...*

Performance wise I am a similar case study to you. Used to race, long lay-off, back into it for fitness only... It took me a while to get the feel of the pedal stroke back. Still not really "there" compared to yesteryear. Speed nothing like the "old days"...

Me - I have 175s on all of my bikes. This is the same length that I used back in the day. 5' 10" with a 33.6 in cycling inseam (855 mm) and long femurs. Changed from 170s for "fashion" reasons. Have not found a reason to change back.

To the OP's queston - I have come to the conclusion that crank arm length is a matter of personal preference as much as anything else. Some people claim to be very effected by it, others not. If I understand it correctly, Bernard Hinault changed crank arm lengths from one day to the next while racing the tour. Longer for mountains and time trials, shorter for the rest of the stages. Bottom line, this is probibly something that is easy to over think...


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## SystemShock (Jun 14, 2008)

Stogaguy said:


> To the OP's queston - I have come to the conclusion that crank arm length is a matter of personal preference as much as anything else. Some people claim to be very effected by it, others not.
> 
> If I understand it correctly, Bernard Hinault changed crank arm lengths from one day to the next while racing the tour. Longer for mountains and time trials, shorter for the rest of the stages. Bottom line, this is probibly something that is easy to over think...


According to Hinault's book,_ Road Racing_, he always used 172.5mm. Even in mountain stages, even in time trials. 

To be fair though, the same book does say that Merckx and Anquetil used longer cranks in the mountains and for TTs.
.


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## brblue (Jan 28, 2003)

*Crank length, pedalling frequency and saddle sores*

I've had a small revelation this weekend and was thinking to share it with you people. Fortunately, this thread was here so, no need to open a new thread on the same topic.
So, presuming you have the time and mood to read, here goes..

90 cm inseam
77,5 cm saddle height
si flite saddle
170 mm cranks 53/39
12-25 cassette

with this setup, i've been pedalling for the past 4-5 years at 110 + rpm (30 km/h on the 39x17 or 39x19, was the usual speed / were the usual gears in flat conditions not too windy etc etc)

when hammering, frequency went UP and I went slowly towards the tip of the saddle.
This functioned great on the flats especially in case of wind.
This sucked on the hills, climbing was very hard and any longer climb (>1km) saw me dragging my but with 10 km/h towards the top.



=> changed my saddle to si max flite, very hard / round on the nose => last 3 years of riding sucked

this saddle placed me further towards the back.
while really cranking it, I was involuntary slipping towards the saddle tip. 
- moving saddle forwards wouldn't help
- shorter stem wouldn't help
- raised saddle a bit - started having more power while needing to reduce frequency

swapped saddles a bunch but not quite happy, still strong need to slide forward


=> changed cranks to 175 compact (50x34)
no more strong tendency to spin up when the going got tough
not much tendency to slip towards the back
(in the meantime, i've started using an 120 mm stem compared to 100 used previously)

=> therefore give the old si max flite another shot => nice ride!
couldn't qualify it else than "mash-tastic" although it' just a feeling (at 30 km/h in the 50X21 it's about 100 rpm which I think is still not really mashing)

ok 1st ride with this saddle / stem / crank combination, for about 2,5 hours, with about 30 min of climbing - hope the next ones will be the same / better 


saddle height 77,5
175 / 50/34
12-25 cassette
setback - about 20 mm more.

I don;t really know if there's a point to this story , other than it's a lot of factors influencing your riding.
Optimal crank length alone will vary in different situations, with different riding styles, setback, saddle type, handlebar drop etc..
happy riding!


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## SystemShock (Jun 14, 2008)

brblue said:


> I've had a small revelation this weekend and was thinking to share it with you people. Fortunately, this thread was here so, no need to open a new thread on the same topic.
> So, presuming you have the time and mood to read, here goes..
> 
> 90 cm inseam
> ...


Interesting and detailed story, thanks for it. 

It makes total sense that your tendency to slide forward on the saddle is now lessened– ppl whose position is too far forward tend to slide forward when going hard. The increased saddle setback and longer cranks may've finally put you far enough behind the cranks to cancel that tendency (though you may want to experiment with even more setback).

Judging from your inseam though, your saddle height might be a little low... 79 or 79.5 might be more like it. The additional power would be nice on the climbs. If you do raise it, don't do it all at once, however. It takes time to get used to a significantly higher saddle position. You'd also have to raise your stem an equal amount to keep your upper body position the same.

Finally... 50x21 seems a little light, gear-wise. Yes, you may be a spinner, but usually you see 100-110 rpm cadences associated with higher power outputs than what it takes to go 30 kph (which is a respectable but not torrid speed). 

You might really be more efficient with the 50x19... still a pretty light/'spinner's' gear. And even if you don't wind up going significantly faster, you might feel less beat after a ride. Of course, it might take a few rides to get used to it. 

Just suggestions. I get the feeling that your position is still in transition, and that there are further gains to be wrung out. But I could be wrong.
.


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## brblue (Jan 28, 2003)

Thanks for the advice!
I'm aware that the saddle is not high enough, but can't do otherwise right now because of lack of mobility...By the advice of the calculator over here http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO
I should have about 80 -82 cm saddle height which is absolutely scary...


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## SystemShock (Jun 14, 2008)

brblue said:


> Thanks for the advice!
> I'm aware that the saddle is not high enough, but can't do otherwise right now because of lack of mobility...By the advice of the calculator over here http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO
> I should have about 80 -82 cm saddle height which is absolutely scary...


If the inseam you inputted is 90cm, the calculator really shouldn't be spitting out a saddle height number above 80.

A saddle height that's too high can cause some pretty serious injuries.  
.


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## tampafw (Jul 25, 2009)

Did you guys make any saddle changes with the newer cranks in either direction....longer or shorter? 

Does longer mean higher saddle position.....or am I backwards?


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## wim (Feb 28, 2005)

tampafw said:


> Did you guys make any saddle changes with the newer cranks in either direction....longer or shorter?
> 
> Does longer mean higher saddle position.....or am I backwards?


The opinions are divided—with a *longer* crank, some people lower the saddle by the difference in crank length, some lower it by half the difference in crank length, some do nothing. As an example, going from *170s to 175s*:

- lowering saddle by 5 mm = same leg extension at crank bottom dead center, pedal 10 mm closer to the chest at top dead center,
- lowering saddle by 2.5 mm = 2.5 mm longer leg extension at crank bottom dead center, pedal 7.5 mm closer to the chest at top dead center,
- doing nothing = 5 mm longer leg extension at crank bottom dead center, pedal 5 mm closer to the chest at top dead center.

_Raising_ the saddle with longer cranks is generally not an option unless there's a real need to keep the knee angle the same at crank top dead center and/or a _significant_ increase in leg extension at bottom dead center is needed, wanted or can be tolerated.


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## freethelemmings (Jul 11, 2009)

I haven't tried this, but it might be worth a try. Peter White suggests a crank length that is 18.5% the length of your leg, from the top of your femur to the ground. Here's the link: http://peterwhitecycles.com/fitting.htm 

If nothing else, his website is pretty fun to read. As to adjusting saddle height, I have adjusted based on where my heel scrapes the middle of the pedal when my hips are in a neutral position on my saddle. Anyone else try this method?

Also, in reference to crank length and pedal circumfrence, I think a better equation to use is Work=Force x Distance. When the amount of Force remains the same, but the Distance is greater, the result is more work. Therefore, I don't agree with Power=Force/Time.


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## newmexrb1 (Aug 16, 2009)

freethelemmings said:


> ...
> Also, in reference to crank length and pedal circumfrence, I think a better equation to use is Work=Force x Distance. When the amount of Force remains the same, but the Distance is greater, the result is more work. Therefore, I don't agree with Power=Force/Time.


I's not Force/time but Power=Work/time. Yes mork work, but takes more time and power remains constant--at least within the limits of optimal muscle loading.


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## Tinea Pedis (Aug 14, 2009)

XCGEEK said:


> First, if you have more than one bike make sure all of your bikes have the same length cranks. I've never heard of any research backing me up, so I may be talking out of my a$$, but I can notice a difference. When I put the same length cranks on my road, TT, cx,and mtb bikes I was definitly more comforatable on all of them


I have 172.5 on one bike and 175 on the other.

No difference could I solely attribute to the cranks that's for sure - as both feel fine. I would certainly fail any blinded test.

I'm 6'1".


I do have to vary the saddle heights though in accordance to the crank lengths. Dropped the saddle by 2.5mm from the 172.5 to the 175 bike - no problems at all


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## dirtysprocket (Feb 9, 2006)

Here is my totally unscientific, anecdotal, and perhaps fatally subjective, but nonetheless firmly held belief: 

2.5mm of arm length does make a difference. Conceptually, I did not think it would matter at all, being such a small change. But I swapped out my crank, with no other changes to the bike, and I find that I have picked up 3-5 rpm in all the places where I was over 90 rpm with the old cranks. Not really noticable at lower rpms. It feels like once I get up to the higher rpms, there is an efficiency boost- sort of like a boat once its on plane. I think the old cranks were loo long/ too big of a circle for me, and now I can spin noticably more freely. (YMMV)

Makes me want to try another 2.5 shorter still!


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## gds (Dec 9, 2008)

2.5mm cranklenth diff. can make a big difference in the way the bike feels. Probably you would need two bikes, exactly the same except for the cranks. Then switch back and forth.

If you increased the cranklength by 2.5mm, you would normally drop your saddle height the same. Generally, saddle height is set by measuring the bend in the knee at the bottom of the stroke. That means you are closer to the pedal by 5mm when the crank comes around to the top. Can you tell the difference when you lower your saddle by 5mm? I can. So switching from 175 to 180 would be like 1cm at the top.


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## Wookiebiker (Sep 5, 2005)

I run shorter cranks for a reason....Short legs an short femurs.

Especially with the short femurs I need a steeper seat tube angle (generally a 74 degree STA)...but I'm 5'11" tall (32.5" inseam) and need a 56cm (or larger) frame and bikes of that size don't come with steeper STA's.

So to compensate for this running a shorter crank brings my foot back and to an extent has a similar effect to a steeper STA.

Another area where it helps is a smaller rotational circle, which means less bend in my knee and my legs are in a more powerful position when I go to the down stroke (the more bend in the knee the less power you have at full bend).

So I run 170mm cranks on my road bike and single speed with 172.5's on my TT bike, but if I had the money I'd change those over to 170's as well.


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## Mr. Versatile (Nov 24, 2005)

I like my cranks to be long, but not too long. I don't like them if they're real short either. There's a couple of different sizes of medium. I'd try one of those.


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## mimason (Oct 7, 2006)

I ride a 56cm TT bike that came wit 175 cranks. I really liked the feel of the bigger circles on hills and general riding but once I jumped in time trial mode doing 10-20k runs I could not find a comfort zone with power and cadence. So I switched to 172.5's like my road bike and everything fell back in place. I typically shift in and out of two gears only for the event. Much better overall for me and no more cramping.


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## shortynolegs (Aug 25, 2009)

What's a good starting point for someone who is 5' 8" with long legs?
I have a 170mm setup but Iooking to change out the crank.


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## Tinea Pedis (Aug 14, 2009)

I would think 170's not a bad place to start.

And I wouldn't really want to go longer than 172.5....


But then, that's just me...


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## Mr. Versatile (Nov 24, 2005)

shortynolegs said:


> What's a good starting point for someone who is 5' 8" with long legs?
> I have a 170mm setup but Iooking to change out the crank.


Why do you want to change it?


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## SystemShock (Jun 14, 2008)

shortynolegs said:


> What's a good starting point for someone who is 5' 8" with long legs?
> I have a 170mm setup but Iooking to change out the crank.


What's your actual inseam length (measured bikie-style, in bare feet, soles to crotch)?

For myself, I'm a short-legged 5'10" with a 32.1" inseam. 172.5 has definitely worked best for me, 175s I've tried and they're too long. 
.


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## mimason (Oct 7, 2006)

5'10 and 32 inseam is not short legged. I think that is normal.


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## CleavesF (Dec 31, 2007)

Let's put it this way. Everyone can use shorter arms... not everyone can use longer ones.


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## SystemShock (Jun 14, 2008)

mimason said:


> 5'10" and 32 inseam is not short legged. I think that is normal.


If you're talking 32" inseam for pants, then yes, it's normal. But I'm talking a 32" inseam as measured for biking... aka crotch-to-floor, in bare feet.

Bernard Hinault's book on road racing listed what the average height and inseam was for pro racers... the figures were 5' 9 1/2" and 33 1/4" (again, biking inseam), respectively. I'm definitely a bit short-legged by those stats.
.


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## DocHunter (Jan 28, 2011)

I have a Cannondale Synapse that was just bought for me by my parents as a gift. I never got the bike fitted to me so I'm doing some research on my own to fit the bike to myself. Oddly, I have no idea what my crank arm length is. 

Here is my bike: http://www.cannondale.com/usa/usaen...ance-Road/Details/1552-9RAS7T-Synapse-Alloy-7

It has an FSA Vero triple crank. It doesn't say anywhere on it what the crank arm length is. Could anyone help me figure out what I have on there?

Thanks!


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## rx-79g (Sep 14, 2010)

DocHunter said:


> I have a Cannondale Synapse that was just bought for me by my parents as a gift. I never got the bike fitted to me so I'm doing some research on my own to fit the bike to myself. Oddly, I have no idea what my crank arm length is.
> 
> Here is my bike: http://www.cannondale.com/usa/usaen...ance-Road/Details/1552-9RAS7T-Synapse-Alloy-7
> 
> ...


It's on the back of the arm.


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## brblue (Jan 28, 2003)

DocHunter said:


> I have a Cannondale Synapse that was just bought for me by my parents as a gift. I never got the bike fitted to me so I'm doing some research on my own to fit the bike to myself. Oddly, I have no idea what my crank arm length is.
> 
> Here is my bike: http://www.cannondale.com/usa/usaen...ance-Road/Details/1552-9RAS7T-Synapse-Alloy-7
> 
> ...


Maybe exchanging cranks is not really the place to start the fitting process..
are frame height / length ok?


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## Gervase (Aug 22, 2009)

I am 5'10", and ride a 175mm crank, then the new cervelo came with 172.5's. I did not know for 3 months, then when talking with a mate about this very subject, realised I had 2 bikes with different cranks.

I went to the bike shop thinking bigger cranks, more purchase, equals more power. The guy who is now one of New Zealands top coaches said, .......I am 6' and I ride 172.5's you should be on those, so stick with them. He said studies show that when you want REAL power, you spin up.....
So I focused on the 2 bikes, now I am very aware of the difference (focus)., I used to get sore knees after 100km in the races, not happened on the shorter cranks.
Pluse bigger cranks give more leverage, but you still need more leg speed, so is there any benefit?
I think it comes down to your style, whether you spin or grind. I know a guy, who is an elite, and 5'6-7" and pushes 180mm cranks, no argument that it works for him? yet very tall guys can ride shorter crank's perhaps like to spin?
Mostly the bike manufacturers also put on the cranks for the size bike that they think is optimal, as they want their bikes to go as fast as possible, to keep the reputation.
I note the first post talking of Zinn, he has created custom cranks, one guy who is 6'6" is now swearing that 210's for him, are where it is at.


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## rubbersoul (Mar 1, 2010)

fiddledoc said:


> Here's a rhetorical question: From where did you pull these figures?
> 
> I'm 5''7", and after using a 170 crank, put on a 172.5. After 9 months, I can still feel the difference, and they feel too large to me. If I buy a new crank, I'll go back to 170. It's not math--it's feel. Either it's comfortable or it's not.



I know where he pulled those figures, it rhymes with grass


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## Gervase (Aug 22, 2009)

rubbersoul said:


> I know where he pulled those figures, it rhymes with grass


you have contributed to the conversation!!


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## Ventruck (Mar 9, 2009)

Been on 170mm's, 172.5mm's, 175mm's, and 181mm's. When running the 172.5's, I thought I was running on 175's the whole time...until I finally looked closer at one of the crank arms. By the time I realized that, I couldn't identify a notable difference between the two lengths. From there, I went to the 170's. My subconscious insisted I lost substantial leverage while my awareness pointed at what was a <1.5% change in length (which calls for <1.5% of torque at a given point assuming force is constant). I know the 181's came off as ridiculously easy to pedal up anything in comparison to others - one of those times where I'd exaggerate, like saying I could climb a vertical surface with them. 

I might be too quick-mouthed in saying there's no good answer. I mean, 170's are ~3% shorter than 175's, and so is the circle. We don't know how much 3% matters. 3% reduction in pedaling circle is inversely a 3% reduction in torque at the horizontal position. As threads regarding stroke point out: fastest riders aren't doing anything too exceptional aside from pushing harder and faster on the downstroke. Furthermore, variation of builds will complicate results and so I don't see a solid principle being made.

All that being said, I am eye-ing a return to 175's. As the other poster(s) mentioned, the decision is a feel thing. I have absolutely no scientifically-proven basis to the move other than "I think I want more leverage at the horizontal position of the downstroke" coming from my time with 170mm's.


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## SlowMover (Jun 6, 2010)

I consistently laugh at guys who ride with longer and longer cranks, develop more and more knee and hip problems, fight with discomfort and all the while claim it's 'what I'm supposed to be riding for my height'. I laugh b/c before the change they had zero issues, but refuse to accept the one change they made is causing the problems. 

6'1"/34.5" inseam/170 compacts and 160's on my P3 tt rig. 

Another guy with my body measurements might ride 180's. Is either one of us wrong? No! The only subset I believe to be wrong are those who have no problems, but go bigger b/c of ego or urban legend and then live with fit problems and injuries. I was doing some scanning of Frank Schleck's ride and we are almost exactly the same height and he is on 172.5's. I doubt many of us would believe a world class pro would be on such 'short' cranks. 

http://autobus.cyclingnews.com/tech/2007/probikes/?id=schleck_cervelo07

Look at LA whom I have stood next to on 2 occasions. He might be 5'9" on a good day....maybe 5'9" b/c I was a full 4+ inches taller and he rides 175's. 

This is along the same lines of the conversations I have with the 'ego' crowd about chain ring sizes.


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## Gervase (Aug 22, 2009)

You have more leverage with longer cranks, yet to utilize that perhaps u need to spin them at the same cadence, therefore you need more leg speed,ie bigger circle. Therefore quite possibly there is no real difference in effort!
As has been pointed out the difference is small, yet it can be noticeable. It seems to me, if you spin well go short, if grind go long. 
On a hill a longer crank with leverage stays in that gear longer keeping the torque up, but u could just equally drop a gear and spin, keeping the torque up?


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## ziscwg (Apr 19, 2010)

I have an mtb with 175 and road bike with 170's. My knees like the 170's better. I feel a bit more "rhythmic" with the 170's in my spinning. I'm thinking of going 170 on my mtb. I will have a bit less leverage, but my 22 ring is still there..........for now. I'm going 2x10 at some point soon


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## looigi (Nov 24, 2010)

See this:

http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf


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## old weightlifter (Apr 21, 2011)

Very interesting topic. as a novice rider shoping for the right bike I noticed that small frames were equiped with 170 cranks mediums with 172.5 and larges with 175. I fall between the small and medium frame (52-54cm) sizes and I really liked the feel of the longer crank on the medium bike but after riding both several times the smaller frame fit my upper body better. but the 170 crank feels too small and I was thinking of switching out to longer cranks . From what I'm reading here for my hight (5 '4") 170 is what I should stay with even though the longer cranks feel better (at least untill I develop a consistant pedal stroke). As a ex weightlifter I am used to more of a full range motion in my legs and I feel like the circle is too small. I like to mash down hard on the pedals (my toes go numb after about 45mins.) so maybe my technique needs polishing before changing out cranks. Anyway I may never be a great cyclist but nothing I have ever done is as fun as riding has been, I am absolutely addicted!


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## Gervase (Aug 22, 2009)

Old Weightlifter, I too used to weights, religiously for 10 years. Getting on the bike, i had to work to get my cadence up. I used to spin around the 70-80 mark, and well, like you I loved the cycling. I never used to be any good at endurance events as a kid, and excelled at sprinting and weights, pressing my own body weight above my head when I was only 18, I could press 220lb. None of that equates to cycling though, and I read that spinning is where it is at.
I used to marvel about the pro's doing from 90-120rpm as a standard performance, ie their range. The thing is I worked at getting the cadence up, and found after about 3 months of working on lifting my cadence that I would look down and discovered (once i bought the cadence comp) that I would be happily sitting at 94rpm. 
That changed my cycling.Now I sit at a minmum of that, and feel happier when really putting the power down at about 104rpm, and when really going for it, even higher.
Think of it like and engine, if your high revving you can produce more power with higher revolutions, and the thing that gets in the way is if your cranks are too long.
if cranks are too long, it is harder to spin? if they are shorter, yes you have less leverage, but you can spin them up faster and then more revs makes up for the shorter cranks. 
for every revolution, I think that you have to go approximately another 16mm travel, for longer cranks. Now this gets all a bit weighed down with statistics, but longer cranks give you more purchase, shorter cranks allow a faster spin, and the longer crank requires more leg speed at the same revolution as a shorter crank.
what i think really determines the crank size is your riding style, if you prefer to grind, go long, if you spin go short. However, I have noticed that there is a good reason bikes don't come out with ridiculously long cranks, ie for 6'6" guys, etc. and that is grinding to my mind is a pretty short duration, ie your anaerobic ability (as you will know from weights) is short lived, ie you will run out of muscle glycogen at the most lasting 90 minutes, where as spinners being more aerobic, might spin all day.......something to consider when doing a ride of a couple of hours or more.
I used to ride with a guy who was a grinder, he was unbeatable till the 79 km mark, then he just faded, no prizes for guessing why...
hope this helps


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## old weightlifter (Apr 21, 2011)

Yes that does help, Thank You! now I know why I fade out after 11/2 - 2hrs! being a gymnast, then sprinter then weightlifter I'm all fast twich and have always been bad at endurance events. I'll do what you suggested and bring up the cadence, smooth out my padel stoke (that might help my feet) and see if my distance times improve. I like your analogy to a high reving engine vs. low rpm I'll go to work on that. Thanks agian!


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## Gervase (Aug 22, 2009)

Old Weightlifter, Great...if I can do it, you can too. My last big race was a tour, 4 days, each day a race, and very hilly. While most had compacts I had a triple with a 26 on the back, it meant while most were grinding up the hills, I was spinning, maintaining 104rpm.
I found that at the fourth day, i was leading the pack, all the others had faded, their muscle's sore from all that grinding, and I was still relatively fresh.
Remember you can still do hill work, in big gears, and 60rpm up hills to keep up the strength, (relatively, not like weight eh... ) but when racing, and of course you have to practice, learn to spin...with that natural or developed strength, and the spinning you will be able to put out some power, that is if spinning suits you...
But you have to try, and do it for some time, devote some time to learning to keep it up in a high cadence. If like me, you may learn that it suits you, then yes you will last longer. Cadence computer is a good tool before getting HR monitor, then ulitmately a power meter.
Happy cycling


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## old weightlifter (Apr 21, 2011)

Awesome! your success gives me motivation! although for now I am riding soley for fun I know my competitive spirit will eventially lead me back into competition, I guess a cadence computer is my next purchase! foget about crank length for now, too many other factors much more important!


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## heathb (Nov 1, 2008)

looigi said:


> See this:
> 
> http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf


Yup that's the article that I read a few months back on this forum. It's all the info you need on this matter.


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## heathb (Nov 1, 2008)

I'm 6'2" with a 34" inseam and I ride 170 and 175 cranks. 

I prefer the 170 cranks as I find my pedaling is smoother and faster.


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## gtino195 (Jun 4, 2013)

I'm 5'9", I'm on a fixed gear with the ratio 15/44 and my cranks are 165 mm . I'm planning to get new crank set and move up to a 46T, I want to get more power and speed when I ride and I'll be hitting the track soon, should I get 165 mm or higher?


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## Sun Rider (Jul 8, 2012)

Here's one approach to determining crank length. How to Fit a Bicycle


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## AvantDale (Dec 26, 2008)

I went from 172.5 to 170 on my road bike and from 175 to 170 on my MTB. I can't tell the difference. :skep:


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## Kerry Irons (Feb 25, 2002)

Sun Rider said:


> Here's one approach to determining crank length. How to Fit a Bicycle


And everyone here wants to thank you for reviving this thread, started 8 years ago with the last comment only 4 years ago.


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## satanas (Nov 8, 2002)

gtino195 said:


> ...should I get 165 mm or higher?


Yes. You don't say what sort of track riding you'll be doing. If sprinting, most people use 165mm for clearance on the banking, otherwise whatever suits. The only way to figure this out is to try different crank lengths yourself(!) - whatever anyone else says isn't necessarily going to work for you.


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## SFTifoso (Aug 17, 2011)

I'm 5'11" and ride 175. I rode 172.5 for a long time, but my legs always felt constricted. Switched to 175 and it was a perfect. A lot of times you just have to listen to your body while you're on the bike. All these formulas people come with are garbage IMO. I know a lot of pro riders would laugh if you tell them they're cranks or seatpost height doesn't fit the "formula".


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## c_h_i_n_a_m_a_n (Mar 3, 2012)

I am using 175 on my MTB and 172.5 on my road bike. It was a conscious decision to go with 172.5 based on a table I saw somewhere. Can I tell the difference? No. It was not my decision for my MTB as I bought my whole first bike from a LBS and they came in that length for that size. And subsequently when I built my own from scratch, I just used what I have been using before.

I am 5'10". 32.5" inseam.


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## wim (Feb 28, 2005)

satanas said:


> If sprinting, most people use 165mm for clearance on the banking, otherwise whatever suits.


Small point, but this would only be true for match sprints during which it's possible to ride at extremely slow speeds or even come to a stop. During sprints in points races, the speeds are always pretty high. So there's never a clearance problem.


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## SkiRacer55 (Apr 29, 2005)

Ditto. I bought a 2008 54 cm Specialized Roubaix, all Apex, 175 mm cranks. I liked the bike but wanted lighter and more performance, so I got a 2012 Specialized Roubaix SL3 Pro and built it up with SRAM Force. I did a BG fit and they tried had me pedal on 3 different 54 cm. frames with 170, 172.5, and 175 cranks. My pedal stroke was choppy on 175, less so on 172.5, very smooth on 170, so that's what I went with...



fiddledoc said:


> Here's a rhetorical question: From where did you pull these figures?
> 
> I'm 5''7", and after using a 170 crank, put on a 172.5. After 9 months, I can still feel the difference, and they feel too large to me. If I buy a new crank, I'll go back to 170. It's not math--it's feel. Either it's comfortable or it's not.


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## satanas (Nov 8, 2002)

wim said:


> Small point, but this would only be true for match sprints during which it's possible to ride at extremely slow speeds or even come to a stop.


Which is what I was referring to, and which is commonly referred to as "sprinting" - as opposed to points races, madisons, etc.

Note to OP: Pay little or no attention to any crank length recommendations based on what has worked for others. The only way to figure out what suits *you* is to try a number of crank lengths, and you need to try a wide enough range that it has included cranks which are definitely too long and too short (for your preference), otherwise you will never be sure that something shorter or longer might not have suited better. Sadly, this takes time, effort and very possibly $.


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## wim (Feb 28, 2005)

satanas said:


> Which is what I was referring to, and which is commonly referred to as "sprinting" - as opposed to points races, madisons, etc.


Well, I've never been able to do much good in a points race without sprinting towards the line every so often. But I know what you're saying.

Good point about things taking time. The body needs to adapt to a change before you can pass judgement on whether something works or not. Sometimes that means weeks or even months.


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## satanas (Nov 8, 2002)

I think that we're basically in agreement about everything except perhaps nomenclature; I wasn't trying to suggest that there is no sprinting in other events, just that clearance on the banking is primarily critical for what you have called "match sprinting" - here in Oz it's usually just called "sprinting" or "track sprinting."


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## wim (Feb 28, 2005)

satanas said:


> I think that we're basically in agreement about everything except perhaps nomenclature


Yes, it's just word meanings we're talking about.

Not sure if you could say something similar about Oz and America, but there's the old saying about this: "England and America are two countries separated by a common language."


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## satanas (Nov 8, 2002)

wim said:


> "England and America are two countries separated by a common language."


That's it - the language is the same, but the idioms do not necessarily match up.


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## Tunnelrat81 (Mar 18, 2007)

Something important that I'm not sure anyone has mentioned yet is range of motion/flexibility. Just last year I (finally) spent some money on a proper fit. I'd had basic fits before, but never from someone with this kind of experience. I was experiencing lower back pain on one size, and it had gotten worse over the last year (incidentally since around the time I'd bought and started riding a mtn. bike.). 

Not long into the fit, and after discussing the problem, the fitter checked out a few things (angles and lengths etc.) and sent me away to purchase 170 crank arms. The one's I'd been riding on my road bike (for 4-5 years) were 172.5. I went off and found some on CL and installed them, and went back for the "all needed parts installed" fitting. Very little else was changed on my overall fit. Stem stayed the same, saddle went up a bit, and not much else. Immediately I could feel the difference and I wasn't getting nearly the back pain I'd been used to. I've been riding that fit since, and the improvement is real.

After my road fit, I went back to the Mtn. bike to transfer my new measurments over (as a starting point) and immediately noticed that the cranks on the Mtn. bike were 175's. That's when I put it together. I had been floating along 'tolerating' the slightly long 172.5 cranks on the road bike for years. As my riding strength/fitness increased, that was slowly causing problems in muscle tightness etc.. But when I started mtn. biking I was thrown even further out of my proper range of motion, and the 'injury' progressed far more quickly.

I now run 170's on both bikes, and the fits feel good, and discomfort is minimal.

My point : For some people, crank length is purely preference. For others, however, our anatomy dictates our allowable arm length.

It just happens that I like a high cadence, so my riding performance, if anything, has improved with the shorter cranks.

-Jeremy


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