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Rear Derailleurs(5 posts)

Rear Derailleurspawistik
Feb 21, 2003 12:57 PM
It seems that most of the cyclocross bikes use road components (except brakes) but some use mtb rear derailleurs or some other mix of road and mtb stuff. Example, the '02 model of Cannondale's cyclocross. What's the difference between an XTR and 105 rear der.?

re: Rear Derailleursatpjunkie
Feb 21, 2003 1:11 PM
MTB derailleurs (rear) use longer cages and allow bigger cassettes. Most Shimano road der. max at 27 teeth. If you plan to use bigger cassettes you have to use a MTB rear der. The downside is the longer cage is more prone to slap and chain drop in a race.
re: Rear Derailleursfeathers mcgraw
Feb 21, 2003 8:16 PM
I have a mtb with a 1x8 drivetrain. It has an ultegra derailer and a 12-32 cassette. I know it's not supposed to, but it works just fine. No problem climbing up to the 32. The short cage keeps things nice and tight.
good to know that it works with single ring, butjiggs
Feb 23, 2003 8:33 AM
do you suspect that it could be a problem with 2 or more rings. I'm thinking large ring/cog combo and chain is too short, or small ring/cog too much chain hanging. I know we shouldn't end up in these combos, but it has happened to me.
may not work for everyone thoughGlowBoy
Feb 24, 2003 4:12 PM
The largest cog a derailleur can clear is dependent partly on how far back the upper pulley can rotate, and it can vary a bit depending on the length of your B-tension screw and the little "outdent" on the derailleur hanger that it pushes off of.

You might find that your Ultegra clears a 32 cog on your current frame, but on a different frame (with the outdent positioned slightly differently) it might not. Then again, installing a longer B-screw could make it work again.

But as mentioned, a "double-chainring" (short cage) road derailleur may not be able to take up enough slack if you used an MTB cassette with double chainrings. Might have to go with the "triple" road derailleur to make it work.