your bike will not shift as smoothly with 32 tooth cog, as it will with a 28, or smaller. In fact an 11-32 is beyond spec for a regular cage rear derailleur.

More importantly, the 11-32 gives you big gaps between gears. If you need the 32 for the low gear that's ok. But if you don't need the low gear, most people prefer smaller jumps between gears.






Depends. If you need a gear lower than 39/28 to easily spin up your toughest climb, then yes. If 39/28 is a low enough gear for you, going to a compact crank is not going to change anything with regard to your knees.

Here's a tool, that may help you wrap your head around some of this:


http://www.gear-calculator.com/#