Crank length...how do you know?

I'd stick with what you have.  Shorter cranks are a recent fad (I use them [165], and like them, but I'm 5'9"), but I think your 172.5s are probably just fine for you. 

Predominant conventional wisdom (depending who you ask, lol) recommends running shorter cranks on your tri/TT bike compared to your road bike setup (for instance, 170 or 172.5 on your tri vs 175 on road) in order to encourage a higher cadence, among other things...  Shorter cranks can also help you be more comfortable in aero.   

However, if it ain't broke, don't fix it.

Cheers, Chris

EDIT: Most online crank calculators are designed for a road-bike setup.  That may or may not be ideal for your tri bike.  As the next poster says, Google will yield an overload of info if you search.  But if you want some super geeky info about tri-bike crank length options, search "crank length" over on Slowtwitch...



Edited by Hydro 2010-07-29 3:48 PM

From the Competitive Cyclist fit calculator:


Cranklength
Few topics can fire up a debate quicker than "What's my ideal cranklength?" We aren't shattering any paradigms with our recommendations here. Rather, we're sticking with the traditional criteria for suggested cranklength. Generally speaking, cranklength is a function of femur length. The longer your femurs, the longer your crankarms should be. Long-legged people, the conventional wisdom states, should take advantage of their inherent leverage by choosing longer arms. Conversely, short-legged people are traditionally steered towards maximizing pedaling efficiency through high RPM's and relatively short crankarms. Googling this topic will possibly provide nearly as many results as "Does God Exist?"


ETA - their tool recommended a 172.5 for me. I am 5'6" but maybe I have a long femur.

Edited by mrbbrad 2010-07-29 3:44 PM

I'll check that out.  I was only thinking a longer crank, not shorter.  I guess I should have worded my post a little better- I wasn't looking for you guys to determine proper length for me, but give me some ideas as to how best to determine the proper length crank.  This link is probably a good start.

Thanks for the info.

Edited by SpeedAgent 2010-07-29 3:50 PM

I"m 6'5" and have the 175 on my road bike. On my tandem i have the 175 and got my wife, who is a beginner cyclist, very short cranks (maybe 165) so she wouldn't feel like she was getting whipped around.

I never switched out to shorter cranks so i can't say if i'd do better or worse with slightly shorter. Do they even make longer? I havent' looked in so long.

I'm 6'1, and relatively long legged.  i've always ridden 175 because that's what came on the frame sizes I'd fit.  With my last bike, paid for by someone else's insurance, I made sure to ask about the crank length.  My fitter thought that considering my size, and that I average a mid-upper 90's cadence when racing, 175 was the best choice and he didn't recommend going shorter.  That's just me though, perhaps if your cadence is lower and you want to get it up the shorter is better.  maybe if your cadence is plenty high, the added leverage of 175 would help.  I'm by no means an expert, just passing on what he told me.

If you have a mountain bike (which usually come with 175's), swap the cranks for a few rides and see how it feels. Or if you don't, maybe a friend would allow you to borrow them for a while?

Yes.  There is 180 in Dura Ace...

ZINN Cylcles (he designs for TALL people) has a calculator and he put me in 185's.  Those would have to be custom and guess who makes custom cranks....  Zinn....

Sadly, you pretty much nailed it down in that statement.
When it comes to things that are hard to "pinpoint" as "X > Y" (Crank length... aerobar bend... drop bar ergonomics... shoes... to a lesser extent saddles) you somewhat are left in the boat of
a.) buying it and hoping for the best
b.) borrowing it from somebody

most bike shops aren't going to let you test ride a different crank for a week or two just to see if you notice a difference :/

Sorry, not the answer you are looking for I'm sure

Just go ask Frank Day (inventor or Power Cranks) over on SlowTwitch.  You'll get more feedback than you can handle.  :-)