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Discussion Starter #1
I recently had knee troubles to the point that I've been off the bike for 6 weeks.
So I got my bike re-fitted along with new shoes, reduced the Q factor to align better with my hips and got custom insoles to correct my feet pronation that could have been the main culprit.
I want to cover all my bases and don't want to be sidelined again so after doing some research online I came along two formulas to figuring out the crank length w/ my inseam being 73cm (28.5 inches)

1. inseam(in cm) x 2.16 = 157 crank
2. (inseam x 1.25) + 65 = 156 crank

That's a big jump from my 170s that came on my bike that I've been riding for years but perhaps having a bad fit for all those years finally caused my injury?
So I just wanted to know if there's anyone out there that has used these formulas and whether they are a good idea. There's some 165mm that I found online for cheap which will be shorter than what i have but going to the 155 or even 160 from Specialites-TA will be a significant investment. Is it worth it? I'll take any feedback! Thanks! :thumbsup:
 

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You're Not the Boss of Me
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Are you sure that's a cycling inseam, not a pants inseam? I'm not that tall and that's three full inches shorter than my cycling inseam. I've also known a lot of small riders, including folks (women, mostly) on 43 cm frames, etc. and no of 'em had cranks under 165. I'm not saying that means anything but...

What size frame are you on (just curious?). What method did you use to arrive at that inseam figure?
 

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Discussion Starter #3
I'm 5'4 3/4'', with a longer torso and short legs. I just remeasured and yes that's my inseam standing with no shoes against the wall up to my crotch (73cm or 28.5 inches)
I now ride a S compact frame but I used to ride a 47 Lemond frame that fit like a glove.
 

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FWIW..
http://www.myra-simon.com/bike/cranks.html
http://www.cptips.com/crnklth.htm
http://www.nettally.com/palmk/Crankset.html
Based on your dimensions, I'd say that you're making a good move by shortening your present crank length..the 'Industry' assumes that most road bikes need a 170mm crank and 39/53t rings and MTB's: a 175mm crank...unless your ability is in the CAT4 or CAT3 category, have you considered dropping the 53t to a 50t???....if you want to consult someone who will not give you any 'BS', contact Peter White; he'll give you expert advice (as well as cranks in stock): http://www.peterwhitecycles.com/
ps: you'll have a few laughs reading his site too.....that's a 'plus' for visiting.
 

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If you want to try smaller cranks, Dotek makes cranks in shorter lengths.You might want to double check but I think they will accept 2 rings. I had a bike with them and they are for double rings. They come in sizes as small as 140mm. The best part is they only cost $29.99
They use 110BCD(mountain) rings.

http://www.danscomp.com/452006.php?cat=PARTS
 

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You're Not the Boss of Me
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The measurement should be not just to your crotch, but up to your sit bones (like you're giving yourself a wedgie). Getting the snugness can add another 3/4 in. I can't find a geometry chart for an old Lemond, but if your cycling inseam were really 28.5, I'd be surprised that you were able to stand over a 47 cm bike w/a horizontal TT.

So, I'm probably hyperanalyzing the measurement because you're proposing a relatively dramatic change based exclusively on the measurement you have.

Sounds like you've been working with a thorough fitter. Does he/she have an opinion?

Ok, I guess I'm not helping much.
 

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Discussion Starter #7
******* said:
FWIW..
Based on your dimensions, I'd say that you're making a good move by shortening your present crank length..the 'Industry' assumes that most road bikes need a 170mm crank and 39/53t rings and MTB's: a 175mm crank...unless your ability is in the CAT4 or CAT3 category, have you considered dropping the 53t to a 50t???....if you want to consult someone who will not give you any 'BS', contact Peter White; he'll give you expert advice (as well as cranks in stock): http://www.peterwhitecycles.com/
ps: you'll have a few laughs reading his site too.....that's a 'plus' for visiting.

*******, thanks for the info. I'll try to give him a call tomorrow. I did check out his website and some of the links you sent where in fact some of the ones too that I found online to define my crank length. I hear what you're talking about re his website, good stuff ;)
I just came back from my local bike shop on my way from work and they said to "do not go under 165" since nobody uses them and because I couldn't get any leverage if they're any shorter. They shrugged my internet research as secondary...they always do.
I haven't tried 50t on the front for road racing. I did have a 46t on my cyclocross bike that I turn into my rainy day/foul weather road bike and I tend to be fine on it but then again I obviously never race with it so I don't know how under geared that could be, I could give that a try too. Thanks for the info!
 

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Discussion Starter #8
Dave Hickey said:
If you want to try smaller cranks, Dotek makes cranks in shorter lengths.You might want to double check but I think they will accept 2 rings. I had a bike with them and they are for double rings. They come in sizes as small as 140mm. The best part is they only cost $29.99
They use 110BCD(mountain) rings.

http://www.danscomp.com/452006.php?cat=PARTS

Wow! $29 bucks! It's worth the try. Were they heavy? This could be the best kept secret in replacement cranks. I think you could have just saved me $300 Nice!
 

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Discussion Starter #9
jtolleson said:
The measurement should be not just to your crotch, but up to your sit bones (like you're giving yourself a wedgie). Getting the snugness can add another 3/4 in. I can't find a geometry chart for an old Lemond, but if your cycling inseam were really 28.5, I'd be surprised that you were able to stand over a 47 cm bike w/a horizontal TT.
Sounds like you've been working with a thorough fitter. Does he/she have an opinion?
Good catch! My old Lemond did in fact have a sloping down tube.
I also did give myself an uncorfortable wedgie w/ a book when taking my inseam measurements so I think it's as close as it's going to get.
The guy that did my bike fit is a reputable one, he's also fitted some guys that are currently in the Tour so I'm taking his bike fit siriously. That said, he didn't measure my inseam and didn't have a solid opinion on getting smaller cranks but advised me on how to change my bike fit if I were to get them. He also said that he wouldn't go smaller than 165 since I tend to do crits and would need the extra leverage.
That's why I'm I needed to hear from other people who have been in the same scenario to see if they have found significant differences between the crank lengths before I made an investment.
Oh and my seat height is 64.5mm to give you an idea. (center of crank to top of seat)
Thanks for you input!
 

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cranks

I am 5'10", 31.5" inseam. I have used 155 cranks for the past 10,000 miles. Your spin will be faster by 5 or 10 rpm's. You have much less stress on your knees because the angle is not so great. I am currently running Rotors, in 155 with 53-39-26 chainrings.
I have made up several Dotek cranks with FSA chainrings. Really easy to make a compact crankset this way since the Doteks are 110 BCD. Doteks are also sold under the name Bulletproof and Redline.
Here is a link to a fellow who sells the complete setup online.
http://bikesmithdesign.com/
You won't regret going to shorter cranks.
Bruce
 

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You're Not the Boss of Me
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You've been very thoughtful and thorough in your process! Sounds like you definitely want/need the shorter cranks, so the only question remains "how much shorter."

Doesn't sound like there's much risk (other than a few bucks) in experimenting with the shorter cranks, so go for it.
 

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Discussion Starter #13
*******,
I talked to Peter White today and talked to him for a few minutes and he has convinced me. He explained to me why it makes sense to go smaller, due to the physical aspect of it and went into the gear ratio differences. I'm convinced too that I should go shorter and he did recommend to try the 155. I just have to figure out the what gears to go with now. I'll look into the links you sent.

Bruce in Texas,
Thanks for the recommendation. I called danscomp.com that Dave Hickey recommended (thanks Dave) and they're out of those for a month. I'm surprised at the price difference. Makes the testing for the right equipment a lot easier on the wallet. I'll try Bikesmith tomorrow to see what they have.

As soon as I get the equipment I'll post back and let you all know! Thanks for all your help!
 

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I have similar stubby measurements so this discussion is of interest to me, I'm sure the real physicists that lurk here will correct me but my theory is shorter cranks in effect increases the gearing so that you can use a smaller chainring to go the same distance which might be a good thing especially since you don't want to end up buzz-sawing your chainstay in half with a big chainring!!

I recall reading MBA magazine several years ago was advertising 180mm cranks for downhillers for "increased leverage" and i was thinking why would you need extra leverage going downhill for- going downhill is leverage enough.
 

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Discussion Starter #15
paper warrior said:
I have similar stubby measurements so this discussion is of interest to me, I'm sure the real physicists that lurk here will correct me but my theory is shorter cranks in effect increases the gearing so that you can use a smaller chainring to go the same distance which might be a good thing especially since you don't want to end up buzz-sawing your chainstay in half with a big chainring!!

I recall reading MBA magazine several years ago was advertising 180mm cranks for downhillers for "increased leverage" and i was thinking why would you need extra leverage going downhill for- going downhill is leverage enough.

paper warrior,
Peter White explained it me too and now it makes sense in my head, in theory, which I've yet to test. He said that a 53t can be brought down to a 50t chainring to get near the same ratio having shortened the crank from 170 to 155. Basically a standard compact crank will do to match the 53/39 . I'm taking his word for it for now and setting it up probably with a 50/36 but increasing the rear cassette to include an 11t as the smallest as opposed to a 12t for sprinting (just in case). That's not a scientific answer but I guess I'm just being a messenger. Cheers.
 

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The funny thing is I posted my other theory couple months ago that 11t cogs wear out real fast. But since I have a problem with math can't really back that up either- how about e=mc2 i guess!!!!!!
 

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Going down 15mm is pretty extreme.

First, if you go down to 155, there is no point in going to a 50x11. It's a bigger gear than a 53x12 -- going to a compact ratio does have it's own merits but it really has nothing to do with crank length.

Second, in the saddle a 155 may allow you to turn a slightly BIGGER gear and possibly generate a little more power. However, going down 15mm when out of the saddle will be a pretty big disadvantage due to the decrease in leverage. You'll probably fatigue a lot faster when climbing out of the saddle or sprinting.

165 is a good compromise for shorter riders. I haven't looked at the formulas you used, but they often also conclude that 6'3" riders use cranks in excess of 200mm. Extreme cranklengths are probably okay for some individuals on the ends of the spectrum, but most (even short or tall riders) can be accomodated by 165-180 cranks.
 

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The "conventional wisdom" holds that 155mm is extreme otherwise they be a lot easier to find and cost a lot more than $30.

But if you think that's extreme hold on to your hat I got a 140mm Sinz crank from some little kid on ebay- a little on the hefty side though who knows that might confer more leverage though I'm having drivetrain alignment problems- gotta check out the empirical evidence!
 

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A thought on leverage.

"Leverage" or lack thereof is often mentioned in crank length discussions as function of the crank alone, probably because it's the most visible and obvious lever. But powering a bicycle involves a number of lever dimensions, all of which are a factor in calculating force at the rear wheel: crank length, chainring radius, rear cog radius, and rear wheel radius.

What complicates all this more is the fact that leverage only figures if the force vector is at right angles to the lever. At the crank, this only happens for a very short segment of the entire pedal stroke, if at all, and depends almost entirely on the pedaling style of the rider.

The point is that optimum crank length is much more complicated than gaining or losing "leverage" at the crank arm. Crank length performance test results vary widely from test to test, leaving it up to the rider to choose crank length by feel and race results.

Two findings about crank length are believed to be true: it takes a long time for the body to adapt to a change in crank length, and casual riders pushing extremely low cadences on flat ground benefit from longer cranks.
 

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Discussion Starter #20
paper warrior said:
The "conventional wisdom" holds that 155mm is extreme otherwise they be a lot easier to find and cost a lot more than $30.

But if you think that's extreme hold on to your hat I got a 140mm Sinz crank from some little kid on ebay- a little on the hefty side though who knows that might confer more leverage though I'm having drivetrain alignment problems- gotta check out the empirical evidence!
warrior,
What kind of alignment issues are you having? Is it FD related?
I was pointed towards the Sinz as a possible solution since the Dotek seem to be out of stock from all the sites that I can find in 155mm and I was told for the Bulletproof that I can't return them if the index shifting doesn't work quite right as quoted below but I wonder if the same applies to the Sinz or the Dotek for that matter.

Bruce in Texas,
Have you experienced any of this with your Doteks? And I quote:
"There may be a problem if you are using Shimano indexed front
shifting. The web between the chainrings on the Doteks and
Bulletproofs is 4.2mm thick. On 9 speed Ultegra or 105 this web is
3.5mm thick.
FSA makes 2 versions of the 110mm bcd 50t road ring. One is
specified as being for 10 speeds. Combined with the wider web it MAY
give approximately 9 speed spacing. I've no way of knowing, and
can't return them if it doesn't"

Currently my setup has an Ultegra 6500 w/ a 68x109.5 bb and I wonder how going with any of these cranks will affect the Q factor if I need to go with longer axel bb for spacing or alignment issues. Did you both have to increase the bb length?
 
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