Crank Arm Lengths

[Wilkinson4]

All, contemplating going to a larger crank but these is so much conflicting info out there. Anybody read this?

http://www.nettally.com/palmk/crderiva.html

Anyway, I am 5'-6 3/4" with a 31.4" inseam. I have ridden 170mm mostly, but I ride 165mm on my fixed gear bike and have 175mm on my mtb's.

I am thinking about going up to 172.5's on a bike being built and I am wondering how it will affect my riding style, especially climbing. Anybody have any insight they want to share or maybe post your inseam and crank arm length here.

Inseam - 79.8mm
Crank - 170mm


mIKE

[Pete Serotta]

Mountain bike has been 175.

Based on your leg length a 170 or 172.5 is what I would recommend.


You being a spinner or a slower RPM would influence it. Spinner would probably prefer 170. I do not think your general performance would be affected so it gets down to your feel of it. Pete

[gone]

Based on your inseam, I'd say 170 is about right. Mine is 34" and I ride 170 on my fixed gear, 175 on road bikes, 180 on my 29'er.

[wasfast]

This gets debated on slowtwitch regularly. There have been links to studies that show almost no different in power due to crank length. One of the studies used a range from 150mm to 200mm.

There has been a trend lately on TT bikes to going shorter. It helps because your leg doesn't come quite as far up at the top of the stroke when you're in the aero position. A couple of guys are using 125mm BMX cranks at the extreme short end of the scale, most 165mm.

I'm 5' 9" and have generally used 170's all my life. I have 172.5's on the TT bike and last year got a pair of 175mm Fulcrum's for the road bike. I can feel a very slight difference on the 175's but mostly the up stroke. Powerwise, undetectable to me.

In your case, 170mm max, shorter if you like

[Ralph]

This is my opinion from 40 years of regular riding.

Ride what's comfortable for you. If you make changes to size of circle your legs make, make sure you know what the changes do (saddle up, down, fore, aft, etc), and how to adjust for them.

At my old age, I have a sensitive butt, and I have less saddle problems with 170's than I do with longer cranks. I'm 5 10". And I use a 52 (or 50 sometimes) in place of a 53, to make up for any leverage I lose with shorter crank....but am aware that with 10 cogs in back to choose from, that makes no difference either.

Sheldon Brown talked about crank arm length and "Gain" ratio. That made sense to me.
http://www.sheldonbrown.com/gain.html

[norcalbiker]

Try them all and then use what you're comfortable with.

I have a 31 inseam and I was told to go for 170 and I did for few years. Until I decided to try a 172.5 and never look back. I also did try a 175 for few rides and did not like it at all.

[RPS]

Anybody have any insight they want to share or maybe post your inseam and crank arm length here.

Mike, I’ve mentioned this before but will repeat it because I think it’s funny and applies directly to this discussion.

A few years back I built a bike on a very temporary basis so I could test it. That included letting a few people, most of whom were very experienced cyclists, ride the bike to get their feedback. As it turned out one of the cranks I used was 170 and the other 172.5 because they came from separate bikes. I didn’t notice anything that different about it for the limited amount of riding I did which surprised me, so I concluded that maybe it was due to leg-length discrepancy (after all 2.5 mm isn’t much). However, after letting each person ride the bike for a significant distance, I asked them if they noticed anything “else” strange beyond what we were testing, and not one mentioned the cranks. I had to tell them afterwards, and they all admitted it had been a non-issue.

I’m not suggesting that 170 and 172.5 are equal, but in my limited blind tests – even on the same bike at the same time – I concluded that it’s not as noticeable as we probably think or expect.



P.S. – Regarding proportional sizing in the article, riders with long inseams and therefore long cranks would likely risk hitting pavement with pedal unless the bike was made with much higher bottom bracket. Bike frames for the most part are not designed “proportionally” and hence if cranks are sized that way it may create some new problems for tall riders. At your height it shouldn’t be an issue. I’d ride what feels good. My inseam is about the same and I mostly ride 170 or 172.5, with 175 on one tandem. On new bikes I buy 172.5.

[bigreen505]

Ride what is comfortable, but don't be afraid to experiment. At the moment I have settled on a 180 because that is the longest crank that is commonly available and I worry that a longer crank would mess up my position. All the calculators say I should use a 185-190. I can spin a 180 crank faster and more steady than a 172.5. Everyone is different.