# Crank length question - 170mm vs 172.5mm



## dd74 (Aug 2, 2007)

What would I gain if I went with a shorter crank? It's been recommended that I use 170mm as opposed to what I now have, which is 172.5mm length cranks. Would I notice a difference? More or less power? Better spin? 2.5mm seems like such a small amount.

Thanks for the advice.


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## Peanya (Jun 12, 2008)

dd74 said:


> 2.5mm seems like such a small amount.


It sounds as if you've answered your question, and suspect right. You could raise your seatpost by that much, and spin better. However, you probably wouldn't be able to feel it. If a pro fitter recommended this, it might be a good idea. If someone just heard your crank length and suggested different, then pay no heed.


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## MR_GRUMPY (Aug 21, 2002)

Are you 5 ft 1" ?????

"What would I gain?"

You might gain the derision of your peers.


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## Squidward (Dec 18, 2005)

You'll probably gain about 10-20 RPM at your maximum cadence. At one point I had cadence sensors on bikes with 170mm, 172.5mm, and 175mm cranks. I noticed that my maximum smooth cadence on each of the bikes went down about 10-20 RPM per 2.5mm increase in crank arm length.


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## waldo425 (Sep 22, 2008)

Slightly higher cadence with a smaller crank.

I put a 165 on my bike to kind of force myself into a higher cadence and have better endurance. I havent noticed any difference with power.


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## cwg_at_opc (Oct 20, 2005)

i primarily ride a tri bike now, so i switched from 172.5 to 170 on
the tri-bike for faster cadence and easier transition to running. i
do miss the extra leverage, especially when climbing, but my cruising
speed is up about 3-5mph. my peak cadence has gone from 105-115
to up around 125, and average cadence has gone up from 75-80 to
about 85 to low 90s.

now when i ride my regular road bike with 172.5's, i notice that my
hip flexors are tighter sooner and the discomfort lasts longer.


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## Kerry Irons (Feb 25, 2002)

*?????????*



cwg_at_opc said:


> i primarily ride a tri bike now, so i switched from 172.5 to 170 on the tri-bike for faster cadence and easier transition to running. i do miss the extra leverage, especially when climbing, but my cruising speed is up about 3-5mph. my peak cadence has gone from 105-115 to up around 125, and average cadence has gone up from 75-80 to about 85 to low 90s.





Squidward said:


> You'll probably gain about 10-20 RPM at your maximum cadence. At one point I had cadence sensors on bikes with 170mm, 172.5mm, and 175mm cranks. I noticed that my maximum smooth cadence on each of the bikes went down about 10-20 RPM per 2.5mm increase in crank arm length.


I can't tell if these guys are serious or just jerkin' your gherkin. The cadence differnce is pretty much proporational to crank length, so 2.5 mm is worth a couple of RPM. Cruising speed up by 3-5 mph? You must be joking! Crank length does NOT have the ability to generate any more power, let alone 30% more power.


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## cwg_at_opc (Oct 20, 2005)

Kerry Irons said:


> I can't tell if these guys are serious or just jerkin' your gherkin. The cadence differnce is pretty much proporational to crank length, so 2.5 mm is worth a couple of RPM. Cruising speed up by 3-5 mph? You must be joking! Crank length does NOT have the ability to generate any more power, let alone 30% more power.


nobody said anything about generating more power.
however i'm able to spin faster, easier, in a higher gear, thus can go faster, how hard is that to get?

before:
Quintana Roo 2008 Caliente, D/A, FSA Team Issue std crank, 172.5, 130BCD, 53/39, 12-25, FP60/Real Design Supersonic 60
average speed for a relatively flat section of road i ride at least three days/week: 18mph

after:
only change: FSA TeamIssue compact, 170, 110BCD, 50/34
average speed for same section of road: 22-23mph
no changes to position other than raising the seat enough to compensate for new crank length
i can spin one gear higher sustained than previously.

yes i know it's a compact, but i'm thinking in terms of gear inches here...

the side benefit to a smaller crank on a steep tri bike is opening up the thigh-torso angle, reduces
strain on the hamstrings, etc.


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## Squidward (Dec 18, 2005)

Yeah, Kerry, what's up?  I pretty much said that as the crank arm length increases the maximum RPMs drop.


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## wim (Feb 28, 2005)

*Offer.*



cwg_at_opc said:


> nobody said anything about generating more power.
> however i'm able to spin faster, easier, in a higher gear, thus can go faster, how hard is that to get?


If you can go faster without having to generate more power, you just revolutionized classical physics. PM me with your formulas and a notarized test protocol. I'll reward you magnificently.


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## EverydayRide (Sep 12, 2008)

dd74 said:


> What would I gain if I went with a shorter crank? It's been recommended that I use 170mm as opposed to what I now have, which is 172.5mm length cranks. Would I notice a difference? More or less power? Better spin? 2.5mm seems like such a small amount.
> 
> Thanks for the advice.


2.5m fore/aft and up/down Think of it as a 5m adjustment that you'll have to compensate over during 70-130 revs a minute


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## MR_GRUMPY (Aug 21, 2002)

When I first went 175, it took me a month to regain my spin. After that month, I was again able to hit 150/160 rpm in spin-outs without bouncing. In the winter months I do MTI's in a huge gear at 55/60 rpm, and my knees haven't fallen off yet.


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## Doctor Who (Feb 22, 2005)

cwg_at_opc said:


> nobody said anything about generating more power.
> however i'm able to spin faster, easier, in a higher gear, thus can go faster, how hard is that to get?


Do you have a powermeter? My guess not. 

I just think you're in better shape now than you were before. Average speed pretty much means squat, unless all testing variables are the same.


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## cwg_at_opc (Oct 20, 2005)

Doctor Who said:


> Do you have a powermeter? My guess not.
> 
> I just think you're in better shape now than you were before. Average speed pretty much means squat, unless all testing variables are the same.



jeez you guys, ease up! (and read my subsequent posts about _my_ variables.)

not a math major, nor physicist, just a recreational rider.
these are my observations from the couple of weeks before the change
and the weeks after. sure, there's probably some improvement in fitness,
but i can't magically improve 30% in the course of three to four weeks either.
as my sig says, i have to work hard just to suck, so when i see/feel
improvements in effort(i.e. easier to pedal faster) - why is that mot a
valid observation?


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## dd74 (Aug 2, 2007)

It's just that I don't want to lose what power I have to climb and sprint. I can always use higher cadence on the flats, though.


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## jmlapoint (Sep 4, 2008)

Crank Length discussions sure gets the blood flowing.


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## brblue (Jan 28, 2003)

Squidward said:


> Yeah, Kerry, what's up?  I pretty much said that as the crank arm length increases the maximum RPMs drop.


It seems that frequency goes up a lot if you drop your saddle a bit. 2-5 mm and.. that's it. I guess that shorter cranks mean also "lower" saddle compared to the cranks' position, besides the smaller circle you're pedalling... however 20 rpm extra seems a lot to me... maybe seat position / cleat position were also modified?


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## Stogaguy (Feb 11, 2006)

*+1*

Your experience parallels mine. Spin is about foot speed and training your muscles to make smooth circles. This is a process that operates somewhat independently of crank arm length. The longer the crank arms the further you must move your foot to complete one revolution of the crank. This is because the crank arm length is the radius of the circle your foot makes with each revolution. A 172.5mm crank is a whopping 1.4% longer than a 170mm crank and therefore should impact your cadence very little.

I moved from 170 to 175 years ago and have never looked back. I did it for increased leverage on the climbs. The difference was noticeable but not large. The impact on my spin as negligible.


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## dd74 (Aug 2, 2007)

Can't lowering the saddle compensate for having "too long" a crankarm?

My newest bike is a traditional frame bike with 170mm cranks. My older bike is a compact frame with a shorter wheelbase and 172.5mm cranks. Both are about equal in weight. But lately, I am able to maintain cadence one gear higher with the older bike than the newer one. I've thought about it and thought about it, and can only come up with the cranks as a potential reason. Am I correct to assume this, or far off base?


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## Puchnuts (Oct 9, 2008)

If your chainrings and cassettes are identical - you could make a good case for the 2.5mm difference in crank-arms being the likely cause for this discrepancy. If not - you're back at square one for a hypothesis.


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## cwg_at_opc (Oct 20, 2005)

i went to Saint Sheldon's and built a table for this discussion:


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## EverydayRide (Sep 12, 2008)

Help me out, I don't understand a single thing on your posted chart.


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## Stogaguy (Feb 11, 2006)

*Sheldon Brown*

The chart is from the late great Sheldon Brown's website. Here is a couple of links.
http://www.sheldonbrown.com/gears/
http://www.sheldonbrown.com/gain.html
Sheldon was a long time bike industry professional. He passed away early last year long before his time. His website is a wealth of information on a wide variety of cycling topics.

The gear chart shows the speed achieved in each gear on the bike at a given rpm at the crank (cadence). Personally, I find this form of reference very helpful when planning/comparing bicycle gearing.


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## cwg_at_opc (Oct 20, 2005)

EverydayRide said:


> Help me out, I don't understand a single thing on your posted chart.


i highlighted(bold and italicized) the key speeds which i was referring to
earlier. the first column is cassette, a 12-25, the next four columns
are two sets: gear inches and [email protected] for a 34/50. the last four
columns are gear inches and [email protected] for a 39/53.

Basically, at 10pedal rpms faster, i can pedal one(or two) gear higher
at the same or less perceived effort, which results in a slightly higher
speed. on Sheldon Brown's website, there is on online gear calculator
which generates these tables. for everybody, i also tried these tables
with the crank length changed to confirm that that has no effect(which
obviously it doesn't, since we're talking about gear inches and [email protected])

(p.s. - stupid excel truncated 172.5 to 173 when i upped the font size)


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## STARNUT (Jun 19, 2005)

dd74 said:


> Can't lowering the saddle compensate for having "too long" a crankarm?



This is how we are taught to set a saddle height, and it's incorrect and assumes a lot about foot size and cleat placement. And your assumption is incorrect. It may be fine and BCD but you knee angle at TDC will be "wonky" and ay more than 110º.

moving on.


as Kerry points out; crank length has jack to do with power. Watts = Force (N m) x Velocity (m/s). Pretty simple if you think about it. It's damn near impossible to buy a crank to short but is possible to buy on to long. The highest ever in-competition recorded wattage was set on a set of 160s and was 2700+ watts. Force _*AND*_ Velocity. People should be buying cranks based on their knee angle at top-dead-center not knee angle at bottom-dead-center. Buy your cranks based on injury prevention not power.

Anyone in doubt, check out Jim Martin's paper.

Starnut (who *gasp* uses a shorter crank on his TT bike than on his road bike)


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## oily666 (Apr 7, 2007)

All the grand numerical and scientific ﻿wazoos aside, I rode 12 years on 175's. This year I'm using 172.5's and everything is better. Better spin, power through a longer part of the pedal stroke, less hip and knee discomfort, better climbing out of the saddle. Average speeds are about what they'd be in early June. Just bought 170's for my touring rig.

Talk amongst yourselves


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## Fredrico (Jun 15, 2002)

Eddy Merckx once said, "If you want to go fast, pedal fast." If you can pedal faster on a 170mm crank, go with it. You're obviously generating more power at the higher cadence on the 170mm crank, because you're going faster.

I'm 5'8" and have a 31" inseam. 175 and 172.5 cranks provide great leverage for my legs, but there's no question for me, 170s are easier to spin. Eddy used 172.5s, Fignon, the guy who lost the TDF by 8 seconds to Greg LeMond in the final TT, rode on 175s. Alot depends on leg length and pedaling style. Trackies use 165s, not only because they're easier to spin on a fixed gear, but also to avoid hitting the track embankment. Forget about leverage. Those guys have the most awesome quads and explosive power, and they're doing above 100 rpm most of the time.

Makes perfect sense spinning a tighter circle at high rpms is more efficient than a with a larger circle. At high rpms, your legs are following the crank around, not taking advantage of the slight leverage advantage of the longer crank arms that would give a slight advantage pushing up a hill at lower cadence.


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## heathb (Nov 1, 2008)

Just get the 170's and go out and ride. You'll have no knee pain, you can hammer just as hard and these types of threads will be a thing of the past. 

You get used to what you ride all the time. I just started back on 170's and I'm loving it for racing. Of course today I had a bad day as I popped three of my chainring bolts off my new DA crank climbing and bent the inner chainring almost in half. So the force is there with these 170 crank arms as I've never done that with my 175 or 177mm DA cranks.


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## dd74 (Aug 2, 2007)

Yeah. I'm going to give 170mm a shot. 

If anyone has a 170mm 53/39 Ultegra or DA crankset for sale, please PM me.


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## EverydayRide (Sep 12, 2008)

cwg_at_opc said:


> i highlighted(bold and italicized) the key speeds which i was referring to
> 
> 
> (p.s. - stupid excel truncated 172.5 to 173 when i upped the font size)


Thanks everyone, that includes Starnut and cwg_at_opc too for the added explanations to the charts.

As what oily666, Fredrico and others have pointed out, crank arm length was a serious topic but seemed to slip through the cracks of bike science this past decade. You buy a frame at X height, you get a crank arm at X length. I've seen the sizing of cranks increase over these past years on road bikes when before it was rare to see anything bigger then 172.5's. You sometimes see 56cm [centre to top seat tube] frames come equipped with 175mm cranks ......I even have a Trek 2100 ZR9000 56cm with 175's as standard. So it's expensive to move around standard features, especially the cost of crank arms now-a-days just to make the fit "FIT."


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## Kerry Irons (Feb 25, 2002)

*Doing the math*



cwg_at_opc said:


> nobody said anything about generating more power. however i'm able to spin faster, easier, in a higher gear, thus can go faster, how hard is that to get?





cwg_at_opc said:


> not a math major, nor physicist


Your second point emphasizes what you don't understand about your first point. If you increase the speed you go on a bicycle, assuming aerodynamic and friction losses don't change, then the ONLY way that can happen is if you are generating more power. So when you say "nobody said anything about generating more power" you are completely incorrect. YOU said you're generating more power when you say you are going faster (given the numbers you state, about 30% more power). There is no reasonable way you can claim that this came from a 2.5 mm change in crank length.

You need to find a time trial course and do a series of TTs in similar weather conditions with the two different cranks. You will find, I am sure, that your time differences are all within normal statistical variation, regardless of which crank length you use.


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## Kerry Irons (Feb 25, 2002)

*Reading backwards*



Squidward said:


> Yeah, Kerry, what's up?  I pretty much said that as the crank arm length increases the maximum RPMs drop.


Sorry, I read the first part of your post thinking you were commenting on an increase in crank length. That said, I can't believe for a minute your statement that "maximum smooth cadence . . . went down about 10-20 RPM per 2.5mm increase in crank arm length."


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## cwg_at_opc (Oct 20, 2005)

Kerry Irons said:


> Your second point emphasizes what you don't understand about your first point. If you increase the speed you go on a bicycle, assuming aerodynamic and friction losses don't change, then the ONLY way that can happen is if you are generating more power. So when you say "nobody said anything about generating more power" you are completely incorrect. YOU said you're generating more power when you say you are going faster (given the numbers you state, about 30% more power). There is no reasonable way you can claim that this came from a 2.5 mm change in crank length.
> 
> You need to find a time trial course and do a series of TTs in similar weather conditions with the two different cranks. You will find, I am sure, that your time differences are all within normal statistical variation, regardless of which crank length you use.



ok. i can agree with that. it's a semantic disconnect here and a lack of clarity
in my verbiage. so i prefer not to call this an argument, because it's not really.

when i think of 'generating' more power i always think in terms of 'quick, easy
weight loss' kind of people who are looking for free no-effort improvements. this is
certainly not the case here, some additional watts are going to the pedals, but
they're spread out over more of the pedal circle, so it seems like less work.

so yeah, i'm pushing a bit harder(not a huge amount), i'm spinning a lot faster
'cause it's easier, and now i'm going faster. this all makes perfect sense to me
even/especially with your correct explanation.

spinning faster is easier with a shorter crank,
it's easier to spin a higher gear at a higher cadence,
higher cadence, higher gears, slightly higher power output, ergo, more speed.

the next argument i expect to hear is: why don't you just spin the 172.5s
at 90rpm and go faster? it's easier for me to spin the 170s in the 90s.

are you happy now?


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## Squidward (Dec 18, 2005)

Kerry Irons said:


> Sorry, I read the first part of your post thinking you were commenting on an increase in crank length. That said, I can't believe for a minute your statement that "maximum smooth cadence . . . went down about 10-20 RPM per 2.5mm increase in crank arm length."


Yeah, I was just joshin' ya.

About the cadence dropping: it's all from memory. Now that I've given it some thought (and the cup of coffee I drank half an hour ago is kicking in) it was a 10 RPM drop per 2.5mm increase. I think my confusion was that between 170mm and 175mm there was a 20 RPM drop so that's where that number came from.


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## Wayne Jacobsen (May 6, 2008)

Sorry for piling on, but the percentage increase in power needed to increase speed from 18 to 22 mph is way more than the percentage difference in speed. If I filled in the boxes correctly on analyticcycling.com, it takes about 103 watts to ride at 18 mph, and about 175 watts to ride at 22mph. With respect, I think this could not have been accomplished by a change in crank length.


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## cwg_at_opc (Oct 20, 2005)

Wayne Jacobsen said:


> Sorry for piling on, but the percentage increase in power needed to increase speed from 18 to 22 mph is way more than the percentage difference in speed. If I filled in the boxes correctly on analyticcycling.com, it takes about 103 watts to ride at 18 mph, and about 175 watts to ride at 22mph. With respect, I think this could not have been accomplished by a change in crank length.


there's no question it will take more watts to go faster, but what would it take
to spin 10rpm faster? it might not feel like a lot more effort since the work is
spread out over more of the rotation.

more question(s):
- is it easier to spin 90rpm(or 100 or faster) on a 170 than a 172.5?
- which is easier to sustain 100rpm for extended periods on a 170 or a 172.5?


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## SystemShock (Jun 14, 2008)

Fredrico said:


> Eddy Merckx once said, "If you want to go fast, pedal fast." If you can pedal faster on a 170mm crank, go with it. You're obviously generating more power at the higher cadence on the 170mm crank, because you're going faster.
> 
> I'm 5'8" and have a 31" inseam. 175 and 172.5 cranks provide great leverage for my legs, but there's no question for me, 170s are easier to spin. * Eddy used 172.5s...*


Not sure about that. If Bernard Hinault's classic book _Road Racing_ is to be believed, Merckx used 175s. Of course, not everyone uses the same crank length throughout their entire career, it's possible he was on 172.5s for awhile.

But with Eddy's long legs (91cm inseam), 175s aren't really a stretch– literally. 
.


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## DM.Aelis (Jun 19, 2007)

cwg_at_opc said:


> there's no question it will take more watts to go faster, but what would it take
> to spin 10rpm faster? it might not feel like a lot more effort since the work is
> spread out over more of the rotation.
> 
> ...


:idea: 

Part of me doesn't even want to join in on this...
but your question(s) make no sense. 

The question you should be asking is

- Is it easier to generate x number of watts at 90rpm or at 50 rpm?

In the example you listed, you preferred shorter cranks because they enabled you to utilize the higher cadence that you found more comfortable. Frankly, watts are watts; but if you like generating the same amount of power at a higher cadence, go for shorter cranks that lend themselves to that faster spin. 

It really doesn't matter at all.


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## Fredrico (Jun 15, 2002)

*Should've looked it up.*



SystemShock said:


> Not sure about that. If Bernard Hinault's classic book _Road Racing_ is to be believed, Merckx used 175s. Of course, not everyone uses the same crank length throughout their entire career, it's possible he was on 172.5s for awhile.
> 
> But with Eddy's long legs (91cm inseam), 175s aren't really a stretch– literally.
> .


I have that book too. The general idea is long leg levers work fine with long cranks, and short legs with short cranks. At a certain point, as some posters have suggested, the circle the legs have to scribe gets too big for an efficient spin, and power starts to drop off.


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## SystemShock (Jun 14, 2008)

*The $64 Dollar Question...*



Fredrico said:


> I have that book too. The general idea is long leg levers work fine with long cranks, and short legs with short cranks. At a certain point, as some posters have suggested, the circle the legs have to scribe gets too big for an efficient spin, and power starts to drop off.


Which brings to mind the 'beeg' fit question: Should crank lengths vary more than they traditionally have?

The 'traditional' thing, after all, was to have almost everybody on 170, 172.5, or 175s... a 3% variation in crankarm lengths. But, ppl's leg lengths obviously vary by much, much more than that.

So, perhaps it's wiser to have a range more like 165mm to 180mm? Even that doesn't match the variation in riders' 'lever' lengths. :idea:

But then I guess we have to 

- ask the really short riders (inseam below 75cm) if 165 feels better than 170 to them
- ask the really big riders (inseam 95cm+) if 180 is better than 175 for them
.


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## Fredrico (Jun 15, 2002)

*Too late!*



DM.Aelis said:


> :idea:
> 
> Part of me doesn't even want to join in on this...
> but your question(s) make no sense.
> ...


Yes it does.

The muscular contractions are shorter on a smaller crank. At high cadences, 95 rpm and above, the legs can't jam on the pedals. There's not enough time. They have no choice but to follow the crank around. This uses the slow twitch muscle fibers. They're the ones that burn oxygen, the aerobic fibers, and can be constantly replenished by the circulatory system.

Jamming purposefully at 50 rpm on long levers, uses, at least a greater proportion of the time, the fast twitch fibers, which fire off of glycogen stored in the fibers. They provide explosive, anaerobic power, but have to ease up and recover at frequent intervals.

So, for reasons of shorter muscular contractions with shorter cranks, and aerobic muscles called into dominance spinning high cadences, it's obvious more sustainable power can be delivered, therefore more speed. That said, it is possible for a long legged rider, like Merckx, to "spin" 175mm cranks, just like a shorter legged rider spins 170.


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## drewmcg (Sep 19, 2005)

*Lots of focused (and some not so focused) thought . . .*

. . . on this topic (by Lennard Zinn) here: http://www.velonews.com/article/5257; This may be better/more current: http://www.zinncycles.com/cranks.php . . .

... and here: http://velonews.com/article/8835.


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## Fredrico (Jun 15, 2002)

*Where's the research?*



SystemShock said:


> Which brings to mind the 'beeg' fit question: Should crank lengths vary more than they traditionally have?
> 
> The 'traditional' thing, after all, was to have almost everybody on 170, 172.5, or 175s... a 3% variation in crankarm lengths. But, ppl's leg lengths obviously vary by much, much more than that.
> 
> ...


Eddy Boresewckxz, the coach with the unspellable name, has some research on crank length in his book, but I can't remember why 170mm became the standard. Other parameters would be bb drop, toe clip overlap, and clearing the chainstays. Entirely logical a longer legged rider could spin a longer crank at high rpms, taking advantage of the slightly increased leverage.

No question, a given rider can train his legs for a given size spinning circle, but there must be a curve of efficient power transfer, that would peak at a given crank length for a given leg length. That could be modified by training, not to mention positioning of the saddle.


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## Fredrico (Jun 15, 2002)

*Thanks!*



drewmcg said:


> . . . on this topic (by Lennard Zinn) here: http://www.velonews.com/article/5257; This may be better/more current: http://www.zinncycles.com/cranks.php . . .
> 
> ... and here: http://velonews.com/article/8835.


Formula, crank length = inseam x .21 (or .216) works for me! I'm 79 cm inseam and have been happiest on 170mm cranks. Zinn makes 200mm cranks for really tall riders, and less than 165mm for really short riders.


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## Mark16q (Oct 19, 2004)

I recently bought a new MTB that came with 170's. I've always ridden 175's. At 5'5" 29" inseam that would seem too long but it's what the old bikes came with and I was comfortable with that length. While I wanted to change the new 170 to 175, I couldn't wait to ride so just gave it a shot.

While I felt like I was getting less power on technical climbs, the higher cadence was nice and I quickly adjusted. But the biggest change was that my previously broken knee no longer ached after long rides. 3 riding days in a row left my knee looking like a melon but now not an issue at all.

Leading to my road bike, which is 172.5. My hip has been bugging me on long road rides lately, and thinking it's time to switch to 170's and compact gearing. My leg strength is there, but my joints are telling me it's time to spin more. If it means going a bit slower but no pain, it's a no brainer.

So now I have to decide what to replace my 10sp DA7800 crank with that doesn't cost a fortune. My new research project  

Mark


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## dd74 (Aug 2, 2007)

Mark16q said:


> I recently bought a new MTB that came with 170's. I've always ridden 175's. At 5'5" 29" inseam that would seem too long but it's what the old bikes came with and I was comfortable with that length. While I wanted to change the new 170 to 175, I couldn't wait to ride so just gave it a shot.
> 
> While I felt like I was getting less power on technical climbs, the higher cadence was nice and I quickly adjusted. But the biggest change was that my previously broken knee no longer ached after long rides. 3 riding days in a row left my knee looking like a melon but now not an issue at all.
> 
> ...


Mark - if you want a compact, you replace your DA7800 with a Shimano R700. Should work right out of the chute.


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## rook (Apr 5, 2009)

*The current thinking on crank length is incredibly flawed*

I really think that the current thinking on crank length is incredibly flawed. That is, many believe that a rider should be on the longest cranks possible that will not lead to a large decrease in ability to spin smoothly. In the 90s, this leverage theory became popularized by Miguel Indurain who had made a switch from 175s to something more fitting his tall frame. I once read that he used 185s, and then even all the way up to 190 and even a custom 192.5 for his hour record attempts. Honestly, I don't think it was the cranks that was making his speed. Cough, cough. If you know what I mean. EPO does many a rider good.

I raced on 175s, got a knee injury playing basketball with some friends and had to have surgery. Came back to cycling and found that I couldn't stay with the best riders on the hills, not because of of lack of fitness mind you. The knee pain was considerable. I switched to 172.5s, and the pain was a little less. Switched again to 170s, the pain was even less. Now, I am on 165s! And no more pain!!!!! I had to adapt my pedaling style on the hills to be more of a spinner instead of more of a big gear masher. However, I can stay with the best and I think that there has been too much theorized in recent years about the so-called leverage advantages of longer cranks.

Even high-level amateurs and pros could use a shift in their thinking on this one. In my opinion now, the shortest crank you can get is the way to go, not the current thinking. I might even experiment further and go with an even shorter crank.


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## drewmcg (Sep 19, 2005)

rook said:


> I really think that the current thinking on crank length is incredibly flawed. That is, many believe that a rider should be on the longest cranks possible that will not lead to a large decrease in ability to spin smoothly. In the 90s, this leverage theory became popularized by Miguel Indurain who had made a switch from 175s to something more fitting his tall frame. I once read that he used 185s, and then even all the way up to 190 and even a custom 192.5 for his hour record attempts. Honestly, I don't think it was the cranks that was making his speed. Cough, cough. If you know what I mean. EPO does many a rider good.
> 
> I raced on 175s, got a knee injury playing basketball with some friends and had to have surgery. Came back to cycling and found that I couldn't stay with the best riders on the hills, not because of of lack of fitness mind you. The knee pain was considerable. I switched to 172.5s, and the pain was a little less. Switched again to 170s, the pain was even less. Now, I am on 165s! And no more pain!!!!! I had to adapt my pedaling style on the hills to be more of a spinner instead of more of a big gear masher. However, I can stay with the best and I think that there has been too much theorized in recent years about the so-called leverage advantages of longer cranks.
> 
> Even high-level amateurs and pros could use a shift in their thinking on this one. In my opinion now, the shortest crank you can get is the way to go, not the current thinking. I might even experiment further and go with an even shorter crank.


How tall are you/ what's your inseam?


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## Mark16q (Oct 19, 2004)

dd74 said:


> Mark - if you want a compact, you replace your DA7800 with a Shimano R700. Should work right out of the chute.


will the DA7800 bb work with the Ultegra compact 6650?

thanks!

Mark


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## rook (Apr 5, 2009)

drewmcg said:


> How tall are you/ what's your inseam?



5" 9 1/2. Can't remember my inseam, but I'm on a fairly standard sized 54.


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## jonm999 (Nov 25, 2021)

dd74 said:


> What would I gain if I went with a shorter crank? It's been recommended that I use 170mm as opposed to what I now have, which is 172.5mm length cranks. Would I notice a difference? More or less power? Better spin? 2.5mm seems like such a small amount.
> 
> Thanks for the advice.


I am 183cm tall with with an 84cm inseam. Using the Height formula 184 x .095 + 65 my crank length should be

I made the small switch from 172.5 to 170 thinking I would gain comfort (nothing about power or speed). Even though some may argue 2.5 is not noticeable I did notice a quicker cadence minutes into my first ride. After 2 months I hated the quicker cadence (purely personal preference) and switched back. I learned that I prefer a slower cadence in one gear harder (longer crank) than a quicker in one gear easier (shorter crank).


dd74 said:


> What would I gain if I went with a shorter crank? It's been recommended that I use 170mm as opposed to what I now have, which is 172.5mm length cranks. Would I notice a difference? More or less power? Better spin? 2.5mm seems like such a small amount.
> 
> Thanks for the advice.


I am 183cm tall with a 84cm inseam and was riding 172.5mm cranks.. Based on the height formula (184 x .095) my crank should be 174.8 (175). However, using the inseam formula (84 x 1.25 + 65) my crank should be 170mm. Thinking I would gain comfort I switched from 172.5 to 170 and, although some might argue this is not noticeable, I noticed a quicker cadence within minutes of my first ride. After 2 months I had to switch back because could not adjust to the quicker cadence, it is just not my riding style. My wife prefers a quicker cadence in an easier gear while i prefer a slower cadence in a harder gear. So. . .If you prefer a quicker cadence go smaller and if you prefer a slower cadence go larger.


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## Lombard (May 8, 2014)

jonm999 said:


> I am 183cm tall with with an 84cm inseam. Using the Height formula 184 x .095 + 65 my crank length should be
> 
> I made the small switch from 172.5 to 170 thinking I would gain comfort (nothing about power or speed). Even though some may argue 2.5 is not noticeable I did notice a quicker cadence minutes into my first ride. After 2 months I hated the quicker cadence (purely personal preference) and switched back. I learned that I prefer a slower cadence in one gear harder (longer crank) than a quicker in one gear easier (shorter crank).
> 
> I am 183cm tall with a 84cm inseam and was riding 172.5mm cranks.. Based on the height formula (184 x .095) my crank should be 174.8 (175). However, using the inseam formula (84 x 1.25 + 65) my crank should be 170mm. Thinking I would gain comfort I switched from 172.5 to 170 and, although some might argue this is not noticeable, I noticed a quicker cadence within minutes of my first ride. After 2 months I had to switch back because could not adjust to the quicker cadence, it is just not my riding style. My wife prefers a quicker cadence in an easier gear while i prefer a slower cadence in a harder gear. So. . .If you prefer a quicker cadence go smaller and if you prefer a slower cadence go larger.


Changing crank lengths will not change your cadence. It will only change the travel distance per revolution which may give you the perception of a faster cadence.


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