All of my bikes currently have a 170 crank on them. I ordered a new compact crank, but inadvertently received a 172.5. Awhile ago, I was thinking of switching to a longer crank, but stayed with the 170. Should I send it back & get a 170 or will the 172.5 be okay. Note I am short at 5’6" but I have a long inseam for my size 30". What are the advantages/disadvantages? Thanks.
2.5mm one way or the other will make very little difference.
but this might be some interesting reading …
http://bicyclecranklength.blogspot.com/
More road/TT focused, but here’s an article I wrote a few years ago
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everyone’s different but here’s my experience. i’m 5’7 32" inseam. i normally ride 170s and i got a set of 172.5mm compacts to use. Adjusted the saddle down of course, but i had bad knee pain for all the rides after the first 40 miles or so. Eventually i just gave up and went back to 170mm and the pain went away.
Since you have the 172.5s and were curious anyway, I would suggest you try them and see how they work. If you don’t like them, sell them or trade them on the classifieds. Since 172.5 is probably the most common size, you should be able to find a buyer. 2.5mm is a pretty small difference and any potential advantages/disadvantages will be purely theoretical and whether theory correlates with practice depends on the individual.
My personal anecdotes is that for many years I lived in the flat midwest and owned bikes with both 172.5 and 175 cranks and didn’t feel much if any difference. Now that I live in a very hilly area, I think that I can feel a slightly better leverage advantage with 175s when climbing and now use 175s on most of my bikes. This is purely subjective though, as I have not done power or time comparisons between crank sizes.
This is funny as I was recently asked why I (I am 5’ 2") have 172.5s on my tri bike - - I have 170s on my cross and road bikes. I don’t have crazy long femurs. I’m pretty proportional for a short person. I guess this might be one of those instances where you are unfortunately going to sink some money down the drain in order to figure out what is best for you.
Back to this person asking me about why I had 172.5s: I had no answer as I’m not smart enough to notice these things on my own - - I consulted with 4 people: three of whom are telling me to get 170s on the tri bike - - one of whom was the fitter who put me on the bike and didn’t realize it had been assembled with the wrong crank arm length. One is my coach (a top age grouper), the third is the former pro cyclist turned fitter who noticed the fact that I had the 172.5s on my bike. The fourth person I consulted is also very knowlegable and a top age grouper and also a coach who said it wasn’t a big deal and that it is actually common to go up slightly in crank arm length for a TT bike - - now a TT not a Tri bike, right, so if you have to run after, maybe that little extra leverage you get in the TT position with a longer crank, is not for triathletes…???
Initially, with this new bike, I had a great deal of knee pain - - don’t know which variable I could attribute that to (new pedal system as well), but at any rate, since the bike was supposed to have 170s and 3 out of 4 experts is telling me to go that way, I’m going to give it a shot…
you probably shouldn’t have 172.5s or 170s on your cross, road, or tri bikes. my guess is that you should be on 165s, or maybe shorter.
put your inseam into kirby palm’s formula, and you may be quite surprised. link to it on top right of this page:
http://bicyclecranklength.blogspot.com/
Wouldn’t knee pain come from not moving the seat fore/aft to adjust for the extra length and keeping the cleat under the knee?
That is interesting, and I do arrive at the 165 crank arm length with that formula…That said, I’ve always been much faster and completely pain free on my road bike with the 170s…and 165 would be yet another suggestion with 3 of the now 5 suggestions pointing to 170…