crank arm length

Somewhere in this book (I read it years ago and so forget details) there is info that says (in a nutshell) that long crank arms are better.
http://www.bikequarterly.com/books_bicycling_science.html

What about your shoe stack height? Having a thicker sole would make your cranks shorter in effect wouldn't it and vice-versa if your shoes had less then it would make your crank longer??

I'm selling brand new 6800 ultegra 172.5's if you want just crank arms (no rings) you can use your existing rings. See classifieds for pics!

Matt

175mm hurts my knees; 172.5mm doesn't.

It's not unusual (cue burst of Tom Jones) for the cranks on recumbents/HPVs to be around the 150 mark, advantages seem to be reduced knee strain/pain and requiring/aiding a faster cadence. AFAIA there's no great argument to say what the length should be, much like the knee-over-pedal-spindle myth, but the powercranks link is interesting. Train with them and you get used to them, allegedly. One proponent of short cranks is Mike Burrows , who can also shorten them for you if the crank allows it.

I'm tempted to try 'em on the next recumbent, in 30-32 on one local 18%-er on a 36+lb 'bent is bloody hard work winching yerself up when you can't stand up for more leverage - dropping to a 26 inner with a short crank might make the difference if it can keep just enough cadence, with the downside of some loss of leverage.

I went from 170 to 175 and noticed no difference at all. And going on the calculations, my teeny legs (length, not girth, haha) should be pedalling 165's!

There's some experimental data that shows shorter cranks are better for power output... because we 'should' be spinning at a high cadence I guess. Here it is:

https://www.powercranks.com/cld.html

The research quoted there - about 3/4 of the way down the page - shows that cyclists produced the most power with quite short cranks. Very odd.

Also if you have sore knees then go shorter, others say.

I think the principle is, whatever works for you.

I quite like shorter cranks as I used to hit the inner pedal on the ground when pedalling through corners. Your experience may be different.

Did I misread this? All the "modern" groupsets I've built have a one-piece driveside crank/spider/BB axle. So while I suppose you could find a chainset minus the rings, it would be unlikely. And as mentioned, buying entire assemblies is almost always must more cost-effective than trying to find parts. (Example - best I could do for a Campy crown race was £16 + postage when I can order an entire headset for £40 with free shipping).

The differences between a standard 170mm crank and the usual "large" 175mm are minimal. Sure, if you are a princess looking for a pea, you might notice. Sheldon had this to say

"I think people really obsess too much about crank length. After all, we all use the same staircases, whether we have long or short legs. Short legged people acclimate their knees to a greater angle of flex to climb stairways, and can also handle proportionally longer cranks than taller people normally use."

http://sheldonbrown.com/cranks.html

I have very long legs (saddle top to BB spindle 84cm) so I buy 175mm cranks and have one touring bike (with an MTB crankset) with 180mm cranks. Both are fine. But if you want the choice of "non-standard" lengths, you need to go to TA Carmina or Middleburn. Bring your bank manager and a data-mining specialist, because neither make it particularly easy to get a set of parts you can actually bolt onto your frame and ride.

Caad 9 - 170mm Campy - saddle crown to pedal axle height is 78cm
Super Six Evo 175 mm ultegra - 73cm
Trek hack 172.5mm 105 - 75.5cm

Can I tell any difference? Can I fuc......

there is a rough guide on:

http://bikedynamics.co.uk/FitGuidecranks.htm

the longer your crank, the manlier you are, fact!

What is your inside leg measurement and what size crank do you use/want to use?

Which cranks do you have? Generally you can replace the arms alone, but it's not always cost-effective to do so. Sometimes you can find a complete set for less.