Crank Arms from 175 to 170 on Ultegra
 

I'm running an Ultegra triple on a 2001 Trek 5200. I would like to change the crank arm length from 175 to 170. What do I have to buy? Can I make the change myself, or should I have my LBS do it?

ThanX!!!!

just buy new crankarms, you can easily do it yourself with just the correct size allen wrench. Just make sure the octalkink lines up correctly before you tighten up the nut. i believe the 2001 is octalink, correct me if i am wrong. Why are you changing size.

I would reccomend taking it to the shop you bought them at and have them do it. it is easy to mis allign the spines causing damage to the arms. if you have more than 1 bike be sure the crank lengths are the same on all of them. 175 is easier to keep the same as most bikes come that way. if you are taller than 5'9 you should be on 175 anyway.

If the bike shop won´t do it for you included in the price , ie they want to charge labour , then look elsewhere because for them , with the tools , it´s a five minute job and those cranks cost real money so they shouldn´t be greedy .

I have an issue with my right knee. I'm hoping that shorter cranks on my road bike will help, as I hit and maintain a higher cadence relative to my other bikes. My other bikes (mountain bikes - one converted into a commuter) all have 175 crank arms. I don't spin @ the same rate with these, so I'm hoping that I can get away with 175 crank arms on those.

I know that some recommend using the same crank length on all one's bikes, while some do not. I'd like to feel the 170's. FYI, I'm 5' 8" with a relatively long lower body compared to the top. :)

I am 5' 8" too. You will like 170. You might need to do other things as well to deal with that knee. Two possible ideas, adjust your cleats so that your foot is a little further away from the crank on the right side. Leather saddles like the B17 accomodate small differences in leg length by stretching. Oh, got a thrid one. Try raising the saddle a tiny little bit.

Lennard Zinn would disagree with you. He rides all different crank lengths and types. My bikes all have either 172.5 or 170 and I'm 5'10.5". Depends on your cadence and spin as well as the state of your knees.

-s

I am 5'8" tall and wear trousers with a 30-inch inseam. I use 170mm cranks almost exclusively, except for 165s on my UO-8, partly because of toe-to-tyre overlap. If you have knee problems, you should use lower gears, particularly with shorter cranks. You may also want to read "Save Your Knees," by James Fox, M.D. (knee specialist and official orthopedic surgeon of the 1984 Olympics).

i am 5'9'' using 175mm is this bad?

No,
I have used 175, gyms seem to use mostly 180 cranks. I think for road bikes with guys about our height, 170 is ideal. But I had 175 on my Mtn bike and never gave it a thought. You could prob spin a little faster with 170's; but if you're happy, we're happy.

It also depends on riding style.

If you like to sprint in the packs then shorter cranks give you higher cadence and more "kick" to keep with the pack.

I like long rides and mountain climbing so I prefer the longer cranks. I still run a high cadence for a brevet type of rider at around 95-100rpm but when I get tired my cadence can drop below 90rpms so the 175s help. They also help with long 1-2hour mountain climbs (a bit more leverage)...

I tend to run the same cranks on all of my bikes but only because things ended up that way.

I have spent a great deal of time agonizong over crank arm length. I wound up coming to the conclusion that it really doesn't matter all that much is you are agonizing over a 2.5mm diffference. A 5mm difference may be more of a stretch, but even then I wonder. I run 175mm mainly because a bike I once bought had them and now I am used to them. I have bikes now with all three of the most popular sizes and the only thing I really notice is what prestonjb points out. A little more leverage with the longer cranks and a bit more sprinting ability with the shorter. In the end though they all seem to get me the same distance in the same time and my overall cadance doesn't fluctuate much (about 2 rpms from 170 to 175 or one rpm per 2.5mm)

There is a website out there where a guy has done a ton of research on crank length. I think you can go to google and put in "proper crank length" and you can find it. His little study says that to notice any differences you have to make considerable jumps in crankarm length.

To answer the actual question that was asked - and I think it has already been answered, yes, you can do it yourself. Just buy the crankarms.

172.5 to 175 i am guessing is not a big deal.

I didn't think so either. But once you go over 100 miles solo I can feel the difference... But for most people and for me most of the time (shorter rides) it is not noticable.

ThanX for all the great replies, folks!!! I'm going to go for the 170mm crank arms. I'll let the group know my impressions after several rides.

ThanX again!!!! :D