Cyclocross - mountain derailleur

I have a bianchi axis an older model and i have xt in the back, whats are the advantages of road derailleurs is it just the lighter weight and the lighter cassette, should i consider switching everything works great so i have a hard time wanting to change anything, I like high cadences and with a 110mm bcp crankset i think i'd have a harder time finding chainrings to keep my high gear ratios

I have an 03 Axis with an XT rear/ultegra front der. I have a friend with a Cross Veloce, and I have ridden his bike quite often---he has the Campy parts. I didn't notice a huge improvement. Besides they look similar with an inch of mud on them! :)

I have an XT (will replace with a Durace) RD on my cross bike. The advantage to a road der. is chain slack. With a short cage RD, you can run less chain links, reducing the chance of chain suck.

The mountain derailleur allows for a wider gear range in back, or so I'm told. I also suspect (but have not looked up numbers to prove it) that the mountain parts are cheaper, as I've most frequently seen that setup on lower-priced CX bikes (ie Axis, TriCross Sport).

Not that there's anything wrong with it, though. One of the best (and fastest) bikes I've ever ridden was had an XTR in back, Dura-Ace in front. And Sora STI brifters. :P But it worked, and well. (and, no, it wasn't mine)

What trick said. Don't get hung up on mtn vs road derailleurs. A lot of it will depend upon what gear range you want to run and whether you have a double or a triple crank.

Somebody correct me if I'm wrong but a believe a short cage RD has a 27t limit...

im pretty sure you're right on flipped, i've got a short cage w/ a 25 and it wont take much more - so i think 27 is its biggest allowable.

the reason that people go to mtn rears from long cage road rears is capacity, so it can take up the chain slack from a huge drop in chainring size or if they are running like a 11-32 or something cassette

"Somebody correct me if I'm wrong but a believe a short cage RD has a 27t limit.."

Pretty close. A 27 is the largest "road" cassette that Shimano makes but a short cage derailleur will handle a 28 for sure and I've heard that you can run a 30 if you're careful about shifting (no big - big combo).

I used to run a 28 tooth sprocket on my MTB with an Ultegra shortcage rear mech without any problems. Also I have no problems running a 28 sprocket on my cross bikes with Campag Veloce or mirage rear mechs