Join Date: Nov 2008
Location: Tampa, FL
Bikes: Norco CCX1, GF HiFi Plus, Dawes SST AL
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Originally Posted by Mudu93
The simple and most economical fix is to get a road front derailure. They are cheap and easy to find. If you must have the XT fd then scrap the brifters and go with barcons like you said.
I already tried a road derailleur that was meant for 50-42-30 rings. Using that part fixes the indexing issue but then the chain drags across the bottom of the derailleur cage when I'm in my smallest ring, a 22, and in the middle of the rear cogs. Doing the math (napkin math so I'm ignoring the seat tube angle to make it simpler) the difference in diameter between my largest (42t) and smallest (22t) ring is 3.503 inches. The difference on the road rings would be 3.184 in. That means the mountain derailleur needs a cage that is .318 inches taller than the one designed for the road rings; though in reality the road cage is taller than it strictly needs to be and an additional .2 would probably be enough to get by here. I guess I could probably get away with using the road derailleur if I used a 24t bottom ring as then the diameter difference would be the same, though the curve of the derailleur cage still wouldn't match the curve of the big ring (but that could be dremel adjusted).
Still even if it worked without extra persuading I don't see how that's cheaper than my proposed method. I can find the ratio and turn myself an adapter pulley on the lathe. I'm not billing my time since this is a personal project so my only cost is a small piece of scrap aluminum, a bolt, and two nylon washers. Hell if I'd stop writing this I probably could have just gone and borrowed a MTB, measured the cable pull and been half way to done in the time I've been responding so far.
Any opinions on whether It would be alright to drill and tap the underside of the downtube about 2-3 inches in front of the bottom bracket? I'm guessing I'd have to helicoil it if I want the threads to be sturdy. This'll be on a 2005 Specialized Hardrock which has a pretty beefy feeling Aluminum frame so I'm thinking it might be ok so long as the pulley is well supported to minimize side-loads since I don't have any metric heli-coils. I really wanted to get it tucked up out of the way but upon further inspection placing it in my first choice location, the back of the seat tube right below the derailleur clamp, won't work very well, there's just not enough space and the angles aren't very good. Underside of the downtube seems a bit more damage prone but the geometry works better.