Depends on what you have on your bike.
I've been looking into changing the 12 - 25 I have on my Cervelo for an 11 - 32. I can manage a 6 mile 5% average grade with it, as is. But on a longer ride, with multiple climbs and anything more than 5%... my knees scream at me. I need to change my derailleur and my chain to switch my cassette. Currently I have SRAM Force on my bike. I need to move to a mid size derailleur to have room for the larger cassette. So, I'll be putting a mid size SRAM Apex derailleur on.
Veronica
You'd have to check your cranks, but i think probably you can just change the 1 chain ring.
If you change out your cassette, you're supposed to get a new chain. Your rear derailleur can probably handle the 11-28 no problem, because my short cage ultegra one did on mine - but there's a slight chance you'll have to get a long cage rear derailleur.
Last edited by Cataboo; 07-26-2010 at 03:55 PM.
No, I think you have to change the whole cassette but others might know more about that. I was just referring to the fact that what you will really notice is the new 28 teeth cog because the rest of the gearing on the 11x28 will be very similar to your current cassette.
For example, your 12x25 cassette is probably 12-13-14-15-16-17-19-21-23-25.
Those numbers represent the teeth on each cog.
When you switch to the 11x28 you might get, lets say:
11-13-15-16-17-19-21-22-25-28
I don't know for sure which 10 cogs you will get (I just guessed at those above) but you as you can see, much of the gearing will be identical to what you already have, what you will really notice is the 28.
Also, looking at Sheldon Brown's site and the gain ratios that different front chain rings and different rear cassettes would produce will show you that all these set ups will have lots of overlaying gears. You just need to figure out which hard gears you need for speed and which light gears you need for climbing based on your experience with hills and your current gearing.
I'm not sure if you would have to change derailleur or chain. I'm not knowledgeable enough.