I have an old 2004 Trek 5200T with a full Ultegra 6500 9 speed drivetrain. Triple 52/42/30 chainring and a 12-25 cassette.
I'd like to do a de facto mullet conversion by swapping in a 9 speed Deore XT rear derailleur (such as the pictured RD-M750-SGS) and 11-34 cassette. I say "de facto" because I don't actually plan to change the triple. My understanding is the 22T difference on the triple would exceed the derailleur's capacity of 43T, but is there any concern if I simply don't use the large chainring?
Any gotchas I'm missing here?
by Wooden-Tree-5160
5 Comments
Size the chain to work in big-big, dont set it up to rip the mech off the frame if you shift into the wrong gear. Much better to have a little slack in small-small
it will work. you can choose to block off either the big chainring or the little one, depending on your use case. just tighten the high or low limit screw to make sure you can’t accidentally shift into an incompatible combination.
Size big-big, avoid cross chaining, worst case scenario if you were to shift small-small, the chain would go slack. Common touring setup, although it’s more common to swap out the 30t granny for a 24t granny, rather than changing the cassette..
I’m running Dura Ace 7700 9s downtube shifters paired to a XTR M952 9s rear derailleur and a 11-34 XT 9s cassette. I have a 46/30 crankset and I run big-big all the time with no issues. Just lock out the 52 with limits like the other commenter said and you’ll be fine.
Mountain and road derailleurs of this era use the same cable pull ratio for shifting. You should be able to slap this on, set the B screw and limit screws, and have good shifting. Avoid cross shifting in big/big and little/little.
Tandems and touring bikes used mtb rear derailleurs for years before mullets were anything other than haircuts.