I just got a Surly Cross Check with the stock Shimano Deore LX (#BB-UN54, 68x113mm) BB, and i want to replace the 175mm triple cranks with something in the 172.5 range. any recommendations? or better yet--teach me how i can search on my own--do i use the 68x113mm measurement to match with the new cranks? how would i phrase the search? never had to do this before....

and under $100 would be nice! thx!

Does the LX come in a shorter version? More to the point, will you notice the 2.5mm? I know of no way (sadly) to search for a crank based on BB spindle length. Would be a nice thing to figure out.

There should be plenty of MTN cranks in 170mm length although I'm not sure if they make MTN specific cranks in the 172.5mm length. I'm not familiar with those specific cranks although the first question is what interface do they use? Are they Octalink, square taper or outboard bearing?

What measurements have you used to decide that you need just a 2.5mm shorter crank? 170mm or even shorter may be better. What's your actual inseam?

Anthony

68mm x 113mm BB, that's what's normally used for triples on road style, which is only part of the equation and has absolutely no correlation with crank length.

UN54 is a shimano cartridge JIS square taper BB, so you can use sugino, older shimano or there abouts.

https://www.sheldonbrown.com/bbsize.html

I'd just take it to the shop you bought it from and ask them if they will swap out the cranks for shorter ones for you.

you need a spindle length that will clear the chainwheel (the front sprocket) from hitting the frame and give you a a straight chainline (cross check a singlespeed??) and no, you most likely won't feel the difference of 2.5mm, if it's a fixed gear and you ride aggressively you might want to find some nice 165mm cranks but you wouldn't need to replace your bb, be careful messin with your drivetrain if you dont work on bikes that often..

thanks to all for the replies. i looked at sheldon's page but really couldn't make much sense out of it tonight, i'l try another time when my mind isn't reeling from work.

I got the bike on ebay, so the shop swap isn't really an option, but i'd prolly just bring it to my LBS anyhow.

BTW i should have mentioned that i want shorter cranks partly because i have knee issues. i've read more than once that cranks too long can exacerbate knee issues, particularly anterior ones.

still happy for any help and specific recommendations!

cheers, m

Let us know what your actual inseam is, crotch to floor standing is socks and we can give you a better opinion on what a good crank length for you is rather than guessing. Nominally I would say that 2.5mm isn't going to make that much difference and I would be going down to at least 170mm but then again if your only around 5' 6" or less then even shorter cranks may be in order.

Anthony

when *i* measure i get 34" -- i'm just shoving the zero end of a tape into my crotchal area and reading where the tape hits the floor. sock feet.

my reasearch on the subject led me HERE regarding a good starting point for crank length choice. and that linked to THIS article suggesting that folks with patellar problems might want to go even 2.5mm shorter. so i'm considering 170mm ranks. i have an older shimano 105 set, a double, but i really have to check the chainline issues.

i'm hoping to find a triple in 170 to replace the 175 triple on my Surly Cross Check. if anyone has a specific suggestion, let me know! (BB info is in the OP!)

OK, your a long legged guy so ANY standard crank length is reasonable for you. I just didn't want to reccomend a crank length of say 170mm and find that you have only a 28" inseam in which case it would still be FAR too long. I recommend cranks to be from 19% to 20.5% of inseam. Now for your inseam, 175mm is still in my recommended range but that doesn't mean that you should stick with them. Everyone is different and my recommendation is based on a range to cover many factors and preferences.

Anyway you probably couldn't go wrong with many lengths but try some 170mm cranks in order to increase the difference. The 105 cranks should work fine. You just have to put them on and see how they work. You will then be able to find out for yourself how the length is and if you like the length but the chainline is wrong you can then get another BB with a shorter spindle.

Another thing I always recommend is that when you go to shorter cranks you usually need to move the saddle rearwards as well as up to compensate. This is assuming that you were positioned near KOPS (knee over pedal spindle) in the first place.

Anthony

I've always liked Sugino cranks.

thanks, anthony, i appreciate it! great advice. Maybe i'll give the 105's a try.

yeah--i have a set on another bike of mine, its a triple, come to think of it! (no granny ring on it at the mo) maybe i should try those if they're the right length...anyway i like them quite alot.