crankset FAQ help

[extra-vert]

Okay, I need some schooling, (again). Anyone know how to decipher all of the 170, 172, 175, compact vrs regular, isis vrs whatever etc?? I have an ultegra crankset. Thinking about switching to an FSA Carbon Pro Elite Compact Isis (something like that). Thoughts, suggestions, help

[KnottedYet]

I guess this might be a good place to start: http://forums.teamestrogen.com/showthread.php?t=9187

I'm about to replace a double with a compact double. LBS guy said I could probably use 175 cranks. Tried a bike with 'em, just to test it. Can't say I noticed any difference. Decided to stick with 170 (like I already have) even though 175 would have given me more power for hills.

[7rider]

I recently switched from an ULtegra triple to a FSA SLK MegaExo compact double. My LBS said MegaExo was replacing the ISIS bottom bracket set up and was "the way to go." Something about being more stiff, better power transfer, yada, yada, yada, and a whole bunch of engineering gobbledy-gook I don't understand. I know that ISIS is a 3-pc. set up vs. 2-pc for MegaExo, which does give me some concern if the bottom bracket needs to be replaced...would I need to replace that whole crankset? I haven't ventured there yet.
I also opted for middle of the road 172.5 crankarms. I thought that's what I had on the Ultegra, but I actually had 175. Other than some slight saddle height adjustments after the rebuild I didn't notice any difference with crankarm length or anything. My bike did lose 2.5 pounds in the process and that helps with hill climbing (now, to shed those 10 lbs off me! That's the harder part!).

[extra-vert]

Wow Regina, a 2.5lb loss??!! That's way more of a difference than I even imagined. Thanks for thw input.

[7rider]

Well, replacing the crank alone didn't account for the 2.5 pounds.
I also replaced the fork and went from all 5 y.o. Ultegra components to full Dura Ace (except for that FSA crank). It was a near total rebuild (wheels remained the same).