General Discussion Triathlon Talk » Crank length Rss Feed  
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2014-04-30 10:47 AM

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Subject: Crank length
I am trying to figure out what length I need. I have searched around and seem to come up with the same formula, Inseam in inches X 5.48 = crank length in mm. This puts me at 172.62 which I would assume I need a 172.5mm crank. Here is the problem though. I read some other articles about my height and inseam and they put me on a 170. I'm 5'10 with a 31.5" inseam.


2014-04-30 10:58 AM
in reply to: Burd

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Regular
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Subject: RE: Crank length
I'm same height and inseam and had mine changed to 145mm. Yep 145. Absolutely love them!!! No dead spot over the top which is really noticed during climbing. Loss of leverage? Nope just go down a gear. Best thing since sliced bread.
2014-04-30 11:06 AM
in reply to: Burd

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Subject: RE: Crank length
the "now" thinking is that you should look at crank length as a fit variable less than a "necessity" for it to be the exact right #.

I've got everything from 175 to 160's and can't tell the difference from one bike to the other.
2014-04-30 11:12 AM
in reply to: Leegoocrap

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over a barrier
Subject: RE: Crank length
where are you guys sourcing shorter cranks? tia.
2014-04-30 11:31 AM
in reply to: tamason

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Subject: RE: Crank length
Originally posted by tamason

I'm same height and inseam and had mine changed to 145mm. Yep 145. Absolutely love them!!! No dead spot over the top which is really noticed during climbing. Loss of leverage? Nope just go down a gear. Best thing since sliced bread.


I have read just about everything I could find on crank lengths, and it seems to be all over the place. Some of the studies that seemed to be better suggest that there is no power loss from 145mm cranks up to 185mm. However you can spin faster with the shorter cranks.

Manufacturers are using 165mm(sometime on smallest bikes in their line) but mostly 170mm, 172.5mm, and 175mm cranks.

All of my bikes (and bike that fit me) have the 172.5mm crank yet all the calculators I have seen put me between 160mm- and 170mm. Under 165mm seems to be difficult to find, so I was thinking to go with 165 but don't know if it's enough for me to feel the difference.

With the shorter cranks you also have to adjust your seat up which would put most people in a more aero position.

Anyone have good sources for reasonably priced cranks at 160mm?
2014-04-30 11:49 AM
in reply to: running2far

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Subject: RE: Crank length
Originally posted by running2far

where are you guys sourcing shorter cranks? tia.


cobb cycling will get you anything down to a 145. Below that you'd probably need to get creative...


2014-04-30 12:07 PM
in reply to: Leegoocrap

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Subject: RE: Crank length

I used to have 170s on all my bikes. Now my tri bike has 150s and I have a 145 crank in a box waiting to be put on that or another bike.

Tri bike shorter cranks can allow more aggressive fit.  Google and read as you will see wide variety of opinions. The difference between the standard 170, 172.5 and 175 is not much but that is what bike part companies think is ideal. Consider that those are supposed to fit people from 4'10" to men well over 6'6", does that make any sense crank length only changes so small.

 

2014-04-30 12:18 PM
in reply to: KathyG

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Subject: RE: Crank length

I ended up calling my friendly LBS after being totally overwhelmed trying to find my own cranks.

Between gearing, bottom brackets, spindle lengths.. I got frustrated and let him pick out a new crank for me.

Ended up with 165mm Shimano 105, after a 172.5mm FSA Gossamer. 

Much better hip angle after the swap and some small adjustments.

2014-04-30 12:36 PM
in reply to: ratherbeswimming

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Subject: RE: Crank length
Interesting info. Funny talking about the much shorter cranks since I saw one calc that put me at a 165mm. So I have data that shows anything from a 165 up to a 172.5. I notice on the SRAM cranks, the smallest they have is a 170. Would it be silly to just fall into the middle of the recommendations and go with the 170mm?
2014-05-02 9:02 AM
in reply to: Burd

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Subject: RE: Crank length
I just had a really lengthy and interesting discussion with my fitter about this issue, since I was swapping to a compact.

My inseam is 870mm, so using the 0.216 factor, that would spit out a monster 187.92mm. 10% of my height would yield 188mm as well. Using the various formulas, which are pretty archaic and probably out-dated, I should be running 185+mm cranks, which is silly.

My 2013 58cm Felt came with 175mm arms. The new Felts run 172.5mm in 58cm frame size. I'm 6'2" with 31.5 inseam (as measured by the fitter - not my pants). I've had no problems with the 175mm cranks, and my fit feels great.

Reading over Dan Empfield's articles on the issue on Slowtwitch, talking to my fitter, and a bunch of other research, I decided to go to the 172.5 for the new crankset. It either won't make a difference, or it may open my hip a bit to let me drop a bit deeper in aero. Either way, seemed like a small issue.

2014-05-02 9:52 AM
in reply to: mirthfuldragon

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Member
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Subject: RE: Crank length
Originally posted by mirthfuldragon

I just had a really lengthy and interesting discussion with my fitter about this issue, since I was swapping to a compact.

My inseam is 870mm, so using the 0.216 factor, that would spit out a monster 187.92mm. 10% of my height would yield 188mm as well. Using the various formulas, which are pretty archaic and probably out-dated, I should be running 185+mm cranks, which is silly.

My 2013 58cm Felt came with 175mm arms. The new Felts run 172.5mm in 58cm frame size. I'm 6'2" with 31.5 inseam (as measured by the fitter - not my pants). I've had no problems with the 175mm cranks, and my fit feels great.

Reading over Dan Empfield's articles on the issue on Slowtwitch, talking to my fitter, and a bunch of other research, I decided to go to the 172.5 for the new crankset. It either won't make a difference, or it may open my hip a bit to let me drop a bit deeper in aero. Either way, seemed like a small issue.




One formula I've seen says you should be using 172.5mm cranks based on your inseam. That same formula says I should be at a 167mm(round up or down?) When I talked to Cob cycling they suggested I go with a 165mm crank, they may have said 160mm except I ride in a hilly area so they kept in up a little.


2014-05-02 10:04 AM
in reply to: Burd

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Subject: RE: Crank length

I don't understand when people say they can't feel the difference in crank length. Either that or I'm a real princess and just don't put a pea under my mattress or I'll get even LESS sleep than I do now... Anyway, I digress. I can definitely feel the difference in crank length, even a 2.5mm difference.

I've got 175's on my MTB, 172.5's on my roadies and TT, and 170's on my track/single speed. I tried 165's on a road bike for about a week -- HATED them. Yeah, I felt like I could turn the pedals over at a slightly higher cadence (more like I HAD to with a slightly lower gear), but felt like I bogged down on hills too quickly.

I used to road race on 175's, counter to what most people thought was best at the time (170's were the most common size). I dropped down to 172.5's first on my TT bike, giving me a little more of an open hip angle at the top of the pedal stroke. Helped a lot with the low front end. I changed over the road bikes soon after for commonality.

Okay, with all that said, whatever you choose, likely the feel of the difference will go away quickly -- within a mile or two. Unless it just isn't for you, in which case it will likely always feel foreign.

2014-05-02 10:50 AM
in reply to: Burd

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Master
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Subject: RE: Crank length

My tri bike came stock with 175s and I rode it that way for several years, then experimented, first going up to 180, then back to 175, then 172.5, and now run 170mm cranks. 

I really LOVE the 170mm cranks. I can easily maintain a 90+ cadence while in aero with NO PAIN in the tendons in the front of my hips, which is what always happened if I tried 90+ with 175 or larger.  At 180mm even 80rpm rides would cause me pain in aero.  That was totally the wrong size for me, and 170 is totally the right size.

I am 6' and 32" inseam, btw.  YMMV.

2014-05-02 10:50 AM
in reply to: briderdt

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Subject: RE: Crank length

Are the formulas you are using to calculate crank length designed for Tri position or road position which are quite different in goals of fit and position.

I can feel differences in crank lengths even of small amount and can adjust but the difference is there.

2014-05-02 12:09 PM
in reply to: briderdt

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Subject: RE: Crank length
Originally posted by briderdt

I don't understand when people say they can't feel the difference in crank length.



Just went from my 170mm road bike with round rings yesterday to my 155 tri bike with Osymetrics today... can't feel a difference there either.
2014-05-02 12:10 PM
in reply to: running2far

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Subject: RE: Crank length

Originally posted by running2far where are you guys sourcing shorter cranks? tia.

I get all mine on eBay.  A simple "dura ace 165" type search finds many.



2014-05-02 3:55 PM
in reply to: brucemorgan

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Elite
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Subject: RE: Crank length

i switched last year to a shorter length as well and am loving it bigtime.  not only on the bike but also on the run, legs just feel much better from the get go out of T2.

2014-05-02 6:47 PM
in reply to: running2far

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Subject: RE: Crank length
Originally posted by running2far

where are you guys sourcing shorter cranks? tia.


I've used 145,155,165,170,172.5. The least expensive and easiest way to do this is switch over to a square taper BB. You can then run bmx Cranks, they are cheap, around $50 a set if I remember correctly in any size you want. You will have to run a 110 bcd ring.

With that said I'm back on 172.5 since I'm using a quarq now and a bike that fits me better.
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