I could really use some advice or clarification on this particular issue I am having concerning the purchase of a new crankset and bottom bracket.

I have been riding almost 10 years and in that time ( I am a little ashamed to admit) I choose not to learn anything about general bicycle mechanics other than how to change a tire.

Over the last year I have made some big steps to become more familiar with my bicycle, mainly out of necessity but the bottom bracket and all the different types, interfaces, sizes, shells, threading and such remain a mystery.

I have a Cannondale CAAD 5, I believe the year is 2003 or 2004 I can't remember which one. I am running Shimano 105 cranks (triple) with Octalink type BB interface. I am assuming the BB type would be a three piece and the threading English.

I have decided that this season I am going to replace all my components and give SRAM a try. I want to now run a compact double chain set with GXP type bottom bracket and ISIS interface.

With that said does anyone see a mechanical problem with this? Have I left out or missed some key information?

Another thing I got confused about was in reading something it appears that Cannondale has designed the BB30 system and been using this on selected bikes since 2001. If I understand correctly BB30 is designed to fit a "thicker" or wider bottom bracket and this also requires a BB30 specific crank or chain set. My Cannondale has a pretty beefy down tube and the BB shell looks doesn't look particularly small. Could it be BB30? I was thinking not due to the Octalink interface.

Okay now I will leave it to you. Anything you might be able to tell would be appreciated.