Swapping a road for a mountain cassette?

[redrhodie]

erm...

no changing derailleurs? No issues going from 10- to 9-speed? Do tell me about the technical details (I can climb over 10 percenters with an 11-27 but I'm still interested)

I had a triple front derailleur (which I had put on in case I decided to do that tour of your 'hood some day ), so I didn't need to change anything but the cassette. If you have a double up front, I think you need to change the rear to a mtb derailleur for it to work. My IRD cassette is 10 speed, so there were no issues there. I'm not technically savvy, so check with a pro before you give it a try.

It shifts great. There may have been some minor adjustments at first, I don't even remember now, it's been a while.