# What determines 172.5mm vs 175mm crank use?



## duffin (Jun 11, 2012)

I suspect it is height? What are the guidelines?

Are there any other variables to consider?


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## tihsepa (Nov 27, 2008)

Nope, center to center.

Spindle to pedal spindle.


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## duffin (Jun 11, 2012)

I found this article.

https://www.stevehoggbikefitting.com/blog/2011/06/crank-length-which-one/


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## tihsepa (Nov 27, 2008)

Sorry, i didnt read the word "use".


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## foto (Feb 7, 2005)

taintal thickness


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## MR_GRUMPY (Aug 21, 2002)

If you are under 5 feet tall, use a 172.5.
.
.
.


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## y2kota (Feb 25, 2013)

duffin said:


> I found this article.
> 
> https://www.stevehoggbikefitting.com/blog/2011/06/crank-length-which-one/


Read though most of it. Good information to take in to consideration. 

Or maybe rename this thread "Having fun with math."


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## ohiorick (May 29, 2010)

its a little less than 1/10 of an inch, so I would say "you" determine which one you want to use. I have bikes with 170, 172.5 and 175 and I can't tell the difference.


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## My Own Private Idaho (Aug 14, 2007)

I doubt you will be able to tell the difference. I've ridden everything from 165's to 180's, and I can't tell the difference between any of them.


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## Kerry Irons (Feb 25, 2002)

duffin said:


> I suspect it is height? What are the guidelines?
> 
> Are there any other variables to consider?


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. 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 tend to 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.

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.

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.

A 2008 study by Jim Martin, Ph.D., from the University of Utah shows zero correlation between crank length and any performance factors.
=============================
Fred Matheny Summary: There have been studies of crankarm length, but the results aren't consistent. Some show that longer cranks provide greater leverage for turning big gears. Some show that shorter cranks foster greater speed via a faster cadence. And some show that crank length is completely individual.

So, longer crankarms aren't a panacea for time trialing. In fact, there are dangers associated with them. The added length makes your knees bend more at the top of pedal strokes and extend more at the bottom -- both of which can lead to biomechanical injuries if you jump from 170 mm to, say, 180 mm.

Also, longer cranks reduce cadence -- and a brisk cadence is the key to good time trialing.


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## mann2 (Oct 16, 2012)

What determines 172.5mm vs 175mm crank use?

leg length


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## SystemShock (Jun 14, 2008)

For me, it was feel. I *could* feel the difference, and that's not too odd when you consider that while there's only a 2.5mm difference in crank arm length between 172.5s and 175s, the pedaling circles those cranks create are 16mm different in size.

175s just felt a little slow and cumbersome to me, while 172.5s were 'ahhh, just right'. But it's a very individual choice, aka YMMV.


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## bolo yeung (Jul 14, 2008)

I swapped to 175 from a 172.5mm crank length (5' 11" with 34.75" inseam). I found a noticeable increase in leverage, but as others have said, my average cadence decreased. At first my knees were hurting a little at the end of each ride but I figured my body was just adapting. After around 8 months or the problem was getting worse so ended up going back to 172.5 which fixed the problem. 

I think the increased height and tighter angle created at the top of the pedal stroke were to blame.


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## PlatyPius (Feb 1, 2009)

What determines the crank length for me is which one is on sale. People who say they can tell the difference (2.5mm) are either smoking crack or experiencing a placebo effect.


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## pmf (Feb 23, 2004)

PlatyPius said:


> What determines the crank length for me is which one is on sale. People who say they can tell the difference (2.5mm) are either smoking crack or experiencing a placebo effect.


Bingo. I went from 172.5 to 175 and could never tell a difference. Why switch? The cranks I wanted were on sale and all they had in stock was 175. The guy selling them said "you'll never notice the difference". He was right. How could you? 2.5 mm is .25 cm, or around 0.1 inches. Hell, cleats and shoe sole thickness probably differ by several times that.


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## SystemShock (Jun 14, 2008)

PlatyPius said:


> What determines the crank length for me is which one is on sale. People who say they can tell the difference (2.5mm) are either smoking crack or experiencing a placebo effect.


What if you've tried 172.5 and 175 side-by-side, did not expect to feel a difference, and, to your surprise, DID feel a difference? 

That was my experience.

– signed, a non-crack-smoker :wink5:


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## hipo_p51 (Jul 6, 2012)

On my newer ride, I switched to 172.5's (175's on the older bike). Per my garmin the RPM's went up a little. Other than that, no noticable difference.


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## cda 455 (Aug 9, 2010)

duffin said:


> I suspect it is height? What are the guidelines?
> 
> Are there any other variables to consider?


I suggest experimenting with crank lengths.


From the time I started riding bikes back in 1970 all the way up until 2010 I used/rode with 175mm cranks. 

Then I started experimenting by using a 170mm crankset for about 6 months. It sucked when I was out of the saddle; felt like a kids tricycle cranks.

Then I bought a 180mm BMX crankset and have been using that for the last year or so. It's awesome when I'm out of the saddle! But when I did my first metric century last Summer I discovered at hour 3.25 of the 4.75 hour ride that those cranks now felt like 200mm! I felt _every revolution_ for the rest of the ride. 

So my next experiment will be using 172.5mm cranks during a metric century and see if my legs will like that length during 3+ hour rides. I'll also do the same with the 170mm cranks.

I want to be able to do centuries and double centuries so finding out that the crank length I like for rides at or less than 3 hours *are not* the crank length I like during the 4th hour and onward! 


For reference, my legs are 33.5" from floor to sit-bones and I have a 32.5" inseam. YMMV


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## foto (Feb 7, 2005)

PlatyPius said:


> What determines the crank length for me is which one is on sale. People who say they can tell the difference (2.5mm) are either smoking crack or experiencing a placebo effect.


lulz. I love your posts.


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## grandsalmon (Jan 18, 2009)

SystemShock said:


> For me, it was feel. I *could* feel the difference, and that's not too odd when you consider that while there's only a 2.5mm difference in crank arm length between 172.5s and 175s, the pedaling circles those cranks create are 16mm different in size.
> 
> 175s just felt a little slow and cumbersome to me, while 172.5s were 'ahhh, just right'. But it's a very individual choice, aka YMMV.


That's the same unassisted-by-drug experience I had. I was strictly 175 coming from a heavy MTB period so goddam many years ago. My road machines started the same, then I took a couple over to 172.5 and my cadence went up and it so felt much better.
Why not the reverse? Simply not.


.


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## camping biker (Dec 22, 2011)

It makes a difference because it changes the angles your knees and foot joints move through on each pedal stroke. 

It also has an effect on your gear ratio just like chainrings and cogs. The difference between a 170mm crank and a 180mm crank arm is 1 cm, but that's 2 cm difference across, and almost 7 cm difference in circumference. At a cadence of 100rpm, thats 700cm a minute more that your foot travels in its circular path. 

I'm new to "gain ratios", but you can calculate the difference with your personal gear set or a model gera set and 2 different size cranks. 

It matters because repetitive stress injuries can be debilitating, and because cranks that are too small can tend to cause riders to "mash" harder than with a "proper" size crank. 

I like 170s on lazy-day bikes, touring bikes, fixed gear bikes. I like 175 on mtn bikes, and 180 on road racing bikes. 

I had 165s on a hardtail mountain bike once and was impressed how fast I could spin them, but dissappointed in what leverage I got. It seemed I had to change gears a lot more often, so I didn't like them. 



pmf said:


> Bingo. I went from 172.5 to 175 and could never tell a difference. Why switch? The cranks I wanted were on sale and all they had in stock was 175. The guy selling them said "you'll never notice the difference". He was right. How could you? 2.5 mm is .25 cm, or around 0.1 inches. Hell, cleats and shoe sole thickness probably differ by several times that.


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## Kerry Irons (Feb 25, 2002)

mann2 said:


> What determines 172.5mm vs 175mm crank use?
> 
> leg length


So, you replied to my post but you obviously did not read it. Makes sense to me.


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## camping biker (Dec 22, 2011)

(sorry for duplicate)


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## camping biker (Dec 22, 2011)

fitting/sizing bike












Kerry Irons said:


> So, you replied to my post but you obviously did not read it. Makes sense to me.


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## DaveW88 (Sep 3, 2006)

camping biker said:


> ...It also has an effect on your gear ratio just like chainrings and cogs. The difference between a 170mm crank and a 180mm crank arm is 1 cm, but that's 2 cm difference across, and almost 7 cm difference in circumference. At a cadence of 100rpm, thats 700cm a minute more that your foot travels in its circular path.


No it does not affect gear ratios. One revolution of the crank is one revolution and for any particular combination of chain wheel and cog the rear wheel will travel the same distance regardless of crank length. The amount of torque applied will be slightly more with a longer crank arm.


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## camping biker (Dec 22, 2011)

True. Excuse me, I meant a difference on your gain ratio. 

For the people who "can't tell any difference", they should get some 155s. They feel more like footpegs than pedals, and you get more ground clearance. LOLolol

Here are some Suntour 160mm triple cranks, for mtn bikes, $60
Sales Promotion!! SR SUNTOUR XCT JR MTB Crankset Bicycle crankset /bicycle crank / bicycle parts/bike parts 160mm 880g-in Bicycle Crank & Chainwheel from Sports & Entertainment on Aliexpress.com 

Variety is the spice of life, so I have a few different bikes, and some have 180, some have 170, one has 175.


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## Mr. Versatile (Nov 24, 2005)

PlatyPius said:


> What determines the crank length for me is which one is on sale. People who say they can tell the difference (2.5mm) are either smoking crack or experiencing a placebo effect.


Yeah, but can you smoke placebos? I rest my case. End of dicussion. Game over.


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## Mr. Versatile (Nov 24, 2005)

What determines 172.5mm vs 175mm crank use? 

Rumors, innuendos & lies. Damnable lies!


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## Mr. Versatile (Nov 24, 2005)

y2kota said:


> Read though most of it. Good information to take in to consideration.
> 
> Or maybe rename this thread "Having fun with math."


*Excuse me!!! *There IS no fun with math. None whatever. You have to remember there are only 3 kinds of people in the world: Those who are good at math & those who aren't.


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## camping biker (Dec 22, 2011)

Oh well. Cranks are sort of a matter of preference, unless you're paying some big deal sports coach to suit you up from helmet to bottom bracket. Try a few sizes and see what works best. If you like 170 or 175 you are in luck, as they're really common sizes. 180s are hard to find for multi-ring cranks, and above 180, it gets expensive! Best of luck.


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## xxl (Mar 19, 2002)

Mr. Versatile said:


> *Excuse me!!! *There IS no fun with math. None whatever. You have to remember there are only 3 kinds of people in the world: Those who are good at math & those who aren't.


Updated for the Digital Age: There are 10 kinds of people in the world; those who understand binary code....


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## skyuen9 (Mar 18, 2013)

I have just ordered my 170mm replacing my 172.5mm. I am hoping it will improve my ride comfort base on theory. 
I am short and has short legs, the current seat set up has the height limited by the down stretch of my legs. i.e. 172.5 from the centre of the crank. The seat is pretty low.
This means when my knees come up, they are higher up and they feel like the thighs are pointing upward over horizontal. Which makes it hard to go on the drop. The whole posture feels cramped.
I am hoping, with the 170mm, my seat height can be 2.5mm higher while keeping the same down stretch, and the angle of the knee is lower during the upstroke. This should improve my comfort in riding on the drop.
Although 2.5mm seems a little. But over all it has 5mm benefits. And whats more, try lifting you knee up another 2.5mm when they are already tight against your body.

I think it is more beneficial for people with shorter legs to go to 170mm. For those who are taller, it is more a matter of taste rather than a restriction.


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## wim (Feb 28, 2005)

skyuen9 said:


> I am hoping, with the 170mm, my seat height can be 2.5mm higher while keeping the same down stretch, and the angle of the knee is lower during the upstroke.


Well, it's more than just hope: if you raise your seat 2.5 mm to accommodate your crank length change, your knee _will be_ 5 mm further away from your upper body and your knee angle _will be_ less at top dead center of the crank circle. 

On the other hand, if you're at the edge of your comfort zone at top dead center with 172.5 mm cranks, these changes aren't going to produce a dramatic improvement. Perhaps you need to raise your seat and handlebar along with it a bit more after you've put some miles on the 170 mm cranks.


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## PlatyPius (Feb 1, 2009)

xxl said:


> Updated for the Digital Age: There are 10 kinds of people in the world; those who understand binary code....


...and those who don't.


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## pmf (Feb 23, 2004)

skyuen9 said:


> I have just ordered my 170mm replacing my 172.5mm. I am hoping it will improve my ride comfort base on theory.
> I am short and has short legs, the current seat set up has the height limited by the down stretch of my legs. i.e. 172.5 from the centre of the crank. The seat is pretty low.
> This means when my knees come up, they are higher up and they feel like the thighs are pointing upward over horizontal. Which makes it hard to go on the drop. The whole posture feels cramped.
> I am hoping, with the 170mm, my seat height can be 2.5mm higher while keeping the same down stretch, and the angle of the knee is lower during the upstroke. This should improve my comfort in riding on the drop.
> ...


You bought a new set of cranks that were a whole 2.5 mm shorter than what you have now. Seriously? You'll never be able to tell the difference. It's 2.5 mm. That's like 0.1 inches. I'd return them and save your money. Try wearing thinner socks.


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## SystemShock (Jun 14, 2008)

pmf said:


> You bought a new set of cranks that were a whole 2.5 mm shorter than what you have now. Seriously? You'll never be able to tell the difference. It's 2.5 mm. That's like 0.1 inches. I'd return them and save your money. Try wearing thinner socks.


Some ppl do notice the difference, though. And while it's only a 2.5mm difference in crankarm length, it's a 16mm difference in the size of the pedaling circle.

The weird part is that I've had this exact same convo with a friend of mine, and it goes about like this:

Him: No one can tell the difference between 172.5s and 175s. It's only 2.5mm. There's no way.
Me: Well, I notice you fiddling around with your seat height, trying to get it perfect. You seem to adjust it almost to the millimeter, so it seems like you can feel small differences there.
Him: But... but... it's not the same thing!
Me: *facepalm*


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## pmf (Feb 23, 2004)

SystemShock said:


> Some ppl do notice the difference, though. And while it's only a 2.5mm difference in crankarm length, it's a 16mm difference in the size of the pedaling circle.
> 
> The weird part is that I've had this exact same convo with a friend of mine, and it goes about like this:
> 
> ...


He's imagining things if he thinks he can even accurately adjust a seat post by one mm. There's not way anyong could tell a difference. The padding in shorts probably differs by several mm. 

There's also those guys extolling the comforts of carbon fiber seat posts ...


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## wim (Feb 28, 2005)

pmf said:


> You'll never be able to tell the difference. It's 2.5 mm. That's like 0.1 inches. I'd return them and save your money. Try wearing thinner socks.


It might be that you can't tell the difference, but there are others who can. It might just be a difference in feel and not performance, but it's a difference.

Also as explained above, the OP's planned 2.5 mm crank length change with a corresponding 2.5 mm change in his saddle height would produce a 5 mm change in effective saddle height at the top of his stroke. Most people who have ridden a bicycle for some time and are attuned to their body will definitely feel that.


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## foto (Feb 7, 2005)

wim said:


> It might be that you can't tell the difference, but there are others who can. It might just be a difference in feel and not performance, but it's a difference.
> 
> Also as explained above, the OP's planned 2.5 mm crank length change with a corresponding 2.5 mm change in his saddle height would produce a 5 mm change in effective saddle height at the top of his stroke. Most people who have ridden a bicycle for some time and are attuned to their body will definitely feel that.


I can tell the difference. But I am also one of these brainwashed suckers who feels like my 23c tires at 90 psi are faster than 28s at 70 psi.


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## foto (Feb 7, 2005)

pmf said:


> He's imagining things if he thinks he can even accurately adjust a seat post by one mm. There's not way anyong could tell a difference. The padding in shorts probably differs by several mm.
> 
> There's also those guys extolling the comforts of carbon fiber seat posts ...


I take it you don't ride much...


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## aclinjury (Sep 12, 2011)

I have knee issues. I use 165mm (at 5'7"). I wish Shimano would make Dura Ace cranks in 160mm.

I'm a strong believer in shorter cranks, especially if you have knee issues or are up there in age. Using short cranks to me feels more natural, like you're walking on your crank arms rather than trying to stomp on them.

For a recreational and even weekend racer, don't worry about the power and torque. Short and long cranks don't make that much of a difference in term of performance. However, a shorter crank CAN make your knee a lot happier in the long run.

Sadly, most of the 160mm cranks I see are for BMX bikes.


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## xjbaylor (Dec 28, 2006)

pmf said:


> There's also those guys extolling the comforts of carbon fiber seat posts ...


Yeah, what idiots.


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## pmf (Feb 23, 2004)

foto said:


> I take it you don't ride much...


I started commuting from Northern VA to DC 21 years ago. Last year I rode a tad under 5000 miles. Most of it was commuting like it has been for the last 9 years since my wife and I had kids and weekends are out for riding. I used to do 7000-8000 miles a week before kids. A week less than 200 miles was wimpy. 

I was riding a monocoque carbon bike (Kestrel 200 Sci) back in the early 1990's when "steel was real". I got a lot of crap back then for riding a "plastic" bike. What were you riding back in 1992? A tricycle?

I've gone through numerous bikes, pedal systems, components, clothes, etc. Remember Bio Pace chain rings? I do. I've seen enough "innovations" in the bike industry to know that most of them are hype. Most of it from personal experience. I've ridden three different crank sizes and could never tell the difference. Same with carbon seat posts. If you really feel a difference, you are certianly a sensitive fellow. 

Take a dollar bill and fold in in half. Now fold it in half three more times. You're looking at 0.375 inches. Now fold that in half if you even can, and you're approximately halfway to 0.1 inches. You're seriously telling me that you can really feel a change in your crank arm length that is that minute? Seriously?

A pair of shoes will differ by more than 2.5mm in sole thickness. Anyone who is spending money replacing cranks to get them 2.5 mm shorter -- stictly for that reason and no cool factor -- is wasting his or her money.


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## foto (Feb 7, 2005)

pmf said:


> I started commuting from Northern VA to DC 21 years ago. Last year I rode a tad under 5000 miles. Most of it was commuting like it has been for the last 9 years since my wife and I had kids and weekends are out for riding. I used to do 7000-8000 miles a week before kids. A week less than 200 miles was wimpy.
> 
> I was riding a monocoque carbon bike (Kestrel 200 Sci) back in the early 1990's when "steel was real". I got a lot of crap back then for riding a "plastic" bike. What were you riding back in 1992? A tricycle?
> 
> ...


yup. Going from a bike with 170 to 172.5 to 175, I feel the difference. Do I care after a while? Not really. And also, I can feel a difference in 1mm of seat post exposure and that really _does_ make a difference to me as rides get longer. I measure my riding in hours, not miles, but I guess riding a lot doesn't necessarily improve your sensitivity to bike fit.

let me guess, you also didn't notice biopace feeling any different either...

Back in 1992 I was riding mountain bikes, but if being older than me makes you feel good, fine you're older than me.


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## foto (Feb 7, 2005)

pmf said:


> I started commuting from Northern VA to DC 21 years ago. Last year I rode a tad under 5000 miles. Most of it was commuting like it has been for the last 9 years since my wife and I had kids and weekends are out for riding. I used to do 7000-8000 miles a week before kids. A week less than 200 miles was wimpy.
> 
> I was riding a monocoque carbon bike (Kestrel 200 Sci) back in the early 1990's when "steel was real". I got a lot of crap back then for riding a "plastic" bike. What were you riding back in 1992? A tricycle?
> 
> ...


Oh, and 8000 miles a week? Wow!, even if you can sustain 20mph over 8000 miles that's 400 hours a week on the bike. And as part of a _commute to an actual job!_ You're right, you do ride a lot!


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## pmf (Feb 23, 2004)

Just because a machine can measure something doesn't mean you can feel it.


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## foto (Feb 7, 2005)

pmf said:


> Just because a machine can measure something doesn't mean you can feel it.


whaa??? Is that what your proctologist told you?


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## pmf (Feb 23, 2004)

foto said:


> Oh, and 8000 miles a week? Wow!, even if you can sustain 20mph over 8000 miles that's 400 hours a week on the bike. And as part of a _commute to an actual job!_ You're right, you do ride a lot!


Sorry, that was meant to be 7k-8k per year. My typo. The next sentence kind of makes that clear. Guess you got me good on that one!

Its kind of jerky to tell someone they don't ride much if they claim they can't tell changes in their seat post or crank length that are the width of a toothpick. 

OK, fine, you're just a really sensitive guy. You should try latex tubes ...


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## cda 455 (Aug 9, 2010)

Mr. Versatile said:


> *Excuse me!!! *There IS no fun with math. None whatever. You have to remember there are only 3 kinds of people in the world: Those who are good at math & those who aren't.



:lol: :lol:


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## Cyclingfan1960 (Apr 5, 2012)

I was once told that it was determined by the type of terrain where you ride... If you ride on a flat area then you don't need as much leverage and you will be fine with a 170, on the other hand if you ride on a hilly terrain then more leverage is needed and a 175 plus will be optimal. Please correct me if I have the wrong idea.

Thanks,


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## foto (Feb 7, 2005)

pmf said:


> Sorry, that was meant to be 7k-8k per year. My typo. The next sentence kind of makes that clear. Guess you got me good on that one!
> 
> Its kind of jerky to tell someone they don't ride much if they claim they can't tell changes in their seat post or crank length that are the width of a toothpick.
> 
> OK, fine, you're just a really sensitive guy. You should try latex tubes ...


Only as jerky as saying someone who notices changes in seatpost height or crank length are imagining things because you have so many miles under your belt and you don't notice.

By the way, crank length is not analogous to the thickness of your soles. That would actually be more like changing bottom bracket height.

That is, unless your shoes are thicker at the top of your pedal stroke, and thinner at the bottom or vice versa.


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## carlislegeorge (Mar 28, 2004)

I love the testiness, and the occasional self-righteousness, that permeates this forum. And this is like the tamest place around.

One of the wrenchs at my LBS, whose judgment I trust most of the time suggested this WRT my 172.5 vs 175 question: Either one will work of course. Like to spin - get the 172.5; like to mash - get the 175.


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## SystemShock (Jun 14, 2008)

carlislegeorge said:


> I love the testiness, and the occasional self-righteousness, that permeates this forum. And this is like the tamest place around.


You should see bikeforums.net – it's much, much worse. It's like where the hardcore poseurs go to post.


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## carlislegeorge (Mar 28, 2004)

I resemble that remark....those folks are pretty tame as well, compared to some...check out velocipedesalon if you haven't already had the pleasure...


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## foto (Feb 7, 2005)

SystemShock said:


> You should see bikeforums.net – it's much, much worse. It's like where the hardcore poseurs go to post.


By "worse" you mean "better", right?


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## SystemShock (Jun 14, 2008)

pmf said:


> He's imagining things if he thinks he can even accurately adjust a seat post by one mm. There's not way anyong could tell a difference. The padding in shorts probably differs by several mm.


Then I guess pro riders are full o' imagination too, since their saddles get carefully adjusted to the millimeter. Far as shorts go, many ppl have a favorite model of one and/or thickness of one, and wear it mostly or exclusively, thus eliminating that as a variable. 

Also consider that it's geometry, too... bend your leg 17 degrees (which is a lot) and you reduce your overall saddle height by only 4 percent when compared to having your leg completely straight. So a few mm in saddle height can change your leg angles significantly, i.e. doesn't take much. 

And I'd probably drop the whole 'you must be imagining it!' line of thinking, really. It's very hard for someone to accurately know what someone else is or isn't thinking, or is or isn't feeling... at least without telepathy or a masters in psychology plus a lot of experience.

Is probably fairer to say, "Well, *I* don't feel or notice it, but some others might." That's kinda cycling in a nutshell, for so many things.


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## cda 455 (Aug 9, 2010)

pmf said:


> He's imagining things if he thinks he can even accurately adjust a seat post by one mm. There's not way anyong could tell a difference. The padding in shorts probably differs by several mm.



Eddy Merckx would disagree with you.


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## foto (Feb 7, 2005)

cda 455 said:


> Eddy Merckx would disagree with you.


That's right, I do.

SURPRISE!!! That's right, I, foto, am the online avatar for cycling legend Eddie Merckx!


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## SystemShock (Jun 14, 2008)

foto said:


> By "worse" you mean "better", right?


LOL. Well, yeah... if one reads cycling forums ironically, I guess.


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## SystemShock (Jun 14, 2008)

carlislegeorge said:


> I resemble that remark....those folks are pretty tame as well, compared to some...


Eh, sorry, but bikeforums.net is a cesspool of poseurdom, pomposity, and abject silliness. RBR has all of these things too, but in diluted form by comparison at least.

The following thread would be a typical example of BF.net 'awesomeness'... 7 pages of name-calling and beating a dead horse into the ground. And not even an interesting horse at that  :

Specialized going mid-compact for 2012


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## xxl (Mar 19, 2002)

SystemShock said:


> Eh, sorry, but bikeforums.net is a cesspool of poseurdom, pomposity, and abject silliness. RBR has all of these things too, but in diluted form by comparison at least.
> 
> The following thread would be a typical example of BF.net 'awesomeness'... 7 pages of name-calling and beating a dead horse into the ground. And not even an interesting horse at that  :
> 
> Specialized going mid-compact for 2012



Yeah, and during all that, not one person bothers to quote the inestimable Cap'n Pissgums:

"Bite my crank, matey!"


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## SystemShock (Jun 14, 2008)

foto said:


> That's right, I do.
> 
> SURPRISE!!! That's right, I, foto, am the online avatar for cycling legend Eddie Merckx!


And I always thought you were way better than Lance, Eddy, even before the whole doping thing blew up in Lance's poop-chute. :thumbsup:


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## Peanya (Jun 12, 2008)

aclinjury said:


> I have knee issues. I use 165mm (at 5'7"). I wish Shimano would make Dura Ace cranks in 160mm.
> 
> I'm a strong believer in shorter cranks, especially if you have knee issues or are up there in age. Using short cranks to me feels more natural, like you're walking on your crank arms rather than trying to stomp on them.
> 
> ...


I'm with you on crank length. Longer cranks for me = knee pain. Although I don't have data to verify my hypothesis, I feel flexibility is also a factor that should be taken into consideration.


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## foto (Feb 7, 2005)

SystemShock said:


> And I always thought you were way better than Lance, Eddy, even before the whole doping thing blew up in Lance's poop-chute. :thumbsup:


As one of his personal friends, I feel its ok for me to say that we have always thought Lance was wound too tight. Even tried to loosen him up by taking him to some Flandarian strip clubs, but both times we went, he got way too drunk and didn't bring any money.


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## nhluhr (Sep 9, 2010)

Kerry Irons said:


> So, you replied to my post but you obviously did not read it. Makes sense to me.


Did YOU read it before you hit the Post button? This post reads like you are a foreign call center cutting and pasting snippets from a script without actually addressing the topic at hand. You're attacking the logic of a crank length formula but the OP didn't ask for a formula. He asked what factors effect crank length changes.



Kerry Irons said:


> 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. 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 tend to 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.
> 
> 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.*
> 
> ...


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## perpetuum_mobile (Nov 30, 2012)

duffin said:


> I suspect it is height? What are the guidelines?
> 
> Are there any other variables to consider?



I am 6'4''. I have ridden 172.5, 175 and 177.5.

With 177.5 I get terrible back and knee pain. It takes me very long to recover from hard efforts.

I can tolerate 175 but it is not optimal.

172.5 feels the best for me. I can do several 100+ mile days in a row and I don't get stiff or sore. I can also tolerate much more aggressive position on the bike with 172.5 rather than with 175 or with 177.5. My cadence also went up after switching to 172.5, now I naturally feel better spinning not mashing. I would even be curious to try out 170 but it would probably be a bit too extreme for me. Right now I am not willing to invest in a new crankset that might not work.

Crank length is not an exact science. Try out several sizes and see which works the best. Longer is not better or more efficient.


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## nhluhr (Sep 9, 2010)

perpetuum_mobile said:


> I am 6'4''. I have ridden 172.5, 175 and 177.5.
> 
> With 177.5 I get terrible back and knee pain. It takes me very long to recover from hard efforts.
> 
> ...


Although I'm nearly the same height, I seem to react opposite to you. I find on my 175 crank bike I tend to self-select a cadence around 100rpm which makes standard gear ratios difficult on climbs. However on my 180 crank bike, I tend to pedal in the 90rpm range and have no trouble using standard ratios. I get more lower back pain from the 175 bike with hard efforts and I tend to stay in the drops for an entire race on the 180 bike. The bikes have identical fits and handlebar dimensions. I have disproportionately long legs/femurs for my height (like, on the extreme end of the bell curve) and I think that probably plays a role but I'd never guess as to what kind of formula one should/could use. FWIW, I've looked at online formulas that attempt to proportion the crank length to your height or femur length and those would have me on something much longer so I don't feel like 180 is an extreme choice by any means and I needed a new crank anyway.

I feel like there's no harm trying other lengths because you may or may not determine it matters for your usage case.


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## ultimobici (Jul 16, 2005)

PlatyPius said:


> What determines the crank length for me is which one is on sale. People who say they can tell the difference (2.5mm) are either smoking crack or experiencing a placebo effect.


I disagree. I started on 170's and was fine. I then went up to 172.5 for several years until a pair of Dura Ace 7410 175 cranks "called" me. Rode em for a few months but couldn't settle on them. Nothing major just sore muscles no matter how easy a ride, just a tad too long. Went back to 172's and everything was fine.


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