Bicycle Mechanics - longer crank arms what will i notice diferrently

i have had 170 cranks thats what came on my bike. if i put on some 172.5 what will i need to do? maybe lower the saddle a bit? or is it not that huge of a jump.

It's 1/8 of an inch. That's not very much. You might not even notice.

You probably will not need to move the saddle, but the longer cranks will feel different. Maybe better, ask your knees after riding on it for a while.

Read this whole thread (especially pages 3 and 4) for a truly exhaustive analysis of all the implications of different crank lengths. :)

http://www.bikeforums.net/showthread.php?t=128549

My guess is you will notice the difference for, maybe, 10 minutes. After that they will feel just like your 170's. I have an MTB refitted for the road that has 175 mm cranks and all of my road bikes have 170's. I barely notice the transition even when riding them back-to-back.

I am height challenged at 66" and experimented in the '70s with 175mm TA cranks and
it was noticeable and annoying compared to 170mm, mainly the slightly larger crank
circle threw me off. The torque variances are small, but larger pedaling circle lead me
rapidly back to 170mm. Altho my ATB is 175, pedaling over wildly varying terrain rather
than smooth asphalt swamps out the difference there, never noticed. A significant
variance is your height, if you are 68-72" especially, you will likely never notice the
change.

I didn't notice the difference between my mtb, roadie, and track bike until someone told me they had different lengths (180, 172.5, and 167.5 respectively). The I felt the difference :D

I had 175s briefly (because they were on hand) and it made my knees hurt. I have bikes with 165s (e.g. the fixie) and 170s, those are both fine.

You will probably have to adjust your seat (if you are picky like me). I upsized from 172.5 to 175 and had to lower my seat a few mills.

I had 172.5 on my road bike and when I went to build up my TT bike, I bought some used 175's on ebay. I liked them so much I decided to get 175's when I upgraded my group.

But really the difference is miniscule. The percentage change between crank arm length is so small compared to other measurements. I was told to try to keep all your cranks the same length between bikes so they all feel the same. But obviously it doesnt apply to track bikes since your crank length is pretty much determined by how steep the banking is.

I have short legs (ride a Small Giant and never taller than a 51 cm frame) and I ride 175's. I used to ride 170's all around - mtb, road, track. Now I have 175's mtb, road, tandem (haven't touched the track bike in a while). I tend to spin till I'm suffering then I push (doesn't everyone?). My strength is sprinting, I can't climb or TT to save my life.

My thoughts on cranks:
http://sprinterdellacasa.blogspot.com/2007/03/how-to-crankarm-lengths.html

Basically I would save significant ergonomic changes for the off season. Significant = crank length, perhaps shoe or pedal swaps if they are radically different. Anything to do with your hips down. bar, stem, seat, etc are not as significant and easy to change back.

hope this helps
cdr