crank length for my gf?

[Shinomaster]

She has a 33" inseam from the you know where to the floor. One formula I came across recommended a pair of 180mm cranks! Does this seem about right??? She is currently using my 172.5 record cranks with no problems. It is very hilly in Portland so a bit of added length may not be a bad thing. I realize there is no one correct answer.

[swoop]

leave her on 172.5's.

[Ken Robb]

Peter Jon White has an interesting article on choosing crank length on his site in which he discusses why Pubic Bone Height isn't as important as femur length. He goes on writing that both measurements just give a good guess as a starting point in any event. There's no absolute substitute for riding experience with different lengths.

My PBH (To me inseam is the second number on the size tag when I buy pants) is 89cm and 170mm cranks are a bit short, 172.5 and 175 feel "right" and 180 was too long. Though I could feel the extra leverage when muscling up short hills I couldn't spin them well and tey also gave me a little discomfort under my patellas because they caused too much flexion I think. ATMO it's better to have cranks a little shorter rather than longer than one's ideal length and that's not even talking about cornering clearance should a rider care about pedaling through corners.

[Too Tall]

Shinosan, "depends" on a bunch of things. What is her peddaling style (toes down etc. etc.) and if she has upper / lower leg lengths which are fairly proportionate matters.

(here is a formula for what that's worth)
20.8% of inseam, +5mm for long femurs, -5mm for short femurs.

Bill Boston is a good read on this. You might gain some insight:

http://www.billbostoncycles.com/crank_length.htm

[EnginCycles]

Shinosan, "depends" on a bunch of things. What is her peddaling style (toes down etc. etc.) and if she has upper / lower leg lengths which are fairly proportionate matters.

The formulas are for situations that are not black or white. you have the rider, the bike and info on her like how she rides plus any body issues that might exist. No formulas needed, just experience and an understanding of how the body and bike work together. I have many clients that are that height and size that prefer and are better off with 170mm cranks. The biggest question is if she can spin or mash. the spinner gets the 170's and the masher gets the 172.5. If they are looking to get better at spinning shorten the cranks.

My $.02

Cheers,
Drew

[SteveP]

shino,
slap yrself in the face for reading stupid shit and leave her alone
s

[AntLockyer]

That formula puts me at 193mm!

I'm more comfortable on the 170s on my fixed than 175s on my geared bike. Weird.

[flick]

I have a 33" inseam and all my bikes have 180mm cranks, just because when the opportunity came along I bought the longer cranks cause longer cranks made sense to ME, I wouldn't switch, I have no problem spinning them, that being said, If I had 175's that were on a bike I doubt I could really tell the difference. In the back of my mind I simply think the added toque from the slightly longer moment arm provides a modicum of advantage without... oh heck no downside to me.

[Roman]

shino,
slap yrself in the face for reading stupid shit and leave her alone
s

this is the clearest and most helpful answer you'll need. really.

[twowheels]

i've seen her legs. 172.5 is perfect.

[rphetteplace]

i've seen her legs. 172.5 is perfect.

we need pics of her legs to really be able to make this call. :)

[giordana93]

in other words, leverage, shmeverage. nothing magic happens when you put a longer crank on, you apply the same amount of force to the pedal. What does happen is that you have effectively lowered the gear (another way of changing leverage on a geared bike, duh). If she has no pain with 172.5s, don't change them unless she absolutely does not know how to spin, in which case a long crank will go with the masher style, but don't expect her to start flying up hills.
the main reason for longer cranks for longer legged folks is they have a greater range of motion that the crank will accomodate. the rest is all formulaic bs, down to the third decimal point.


see Sheldon for this:
http://www.sheldonbrown.com/cranks.html

[Shawn G]

I just gotta say, the thread title is disturbing at best.

Shawn G

[Chance Legstrong]

this thread is useless without proper visual aids...please post pics of said legs.

[mschol17]

I think questions about the crank length she needs vs the crank length available are personal and should be addressed in private between you and her.

[jerk]

it doesn't matter. she should use what ever she is used to.

jerk

[weirdo]

Don't rule out black cranks.

[rphetteplace]

she should try out a whole bunch of different crank sizes and see what works best for her

[swoop]

i'm shutting this one off. its just shino's 'innocent troll' schtick. the guy has been riding for years and years and on forums for years and years and always dances on the edge of troll and plays the innocent beginner and we have already indulged it enough.

assuming your g/f is an adult... she'll figure it out or you two can save your pennies and have one of the well informed locals, amazing shops or your experienced team mates talk to her.