I currently have an older trek road bike with indexed downtube shifters. I've been doing some touring on this bike and now want to put a triple crank on it. I've got a new long cage rear derailluer, the correct bottom bracket, and a sugino triple crank, my question is do I need a new front derailluer as well? the current set-up on the bike is a double crankset.
hm...i'm might get this wrong, but i'll take a shot at it. since it's indexed, all you'll need is a new shifter. I THINK. it's possble that the front derailleur was just made for two chainrings, but i'm willing to bet it can be made to work with a triple. if not, i think you could go friction shifting and definitly make it work.
Originally Posted by caloso
I learned this the hard way. They say that experience is the best teacher, but I would have been preferred to just read about it on the internet.
1986 Bridgestone 500, 1981 Motobecane Super Mirage
You will likely need a new front derailleur as well, to handle the larger difference between the front cranks. This would depend on the model of your existing front derailleur.
Depending on the cranks, you could keep the double and swap the chainrings to a smaller size. Moving from say, a 42/52 to a 34/48 would offer a much lower gear for climbing. Unfortunately this option is probably no cheaper than a larger capacity front derailleur.
You would also want a triple FD for the profile. You could probably shift a triple crank with a double FD, but it wouldn't work so well. Triple FDs have extra room where they need it and lumps and bumps to push your chain in the right places.
You will probably need a new front derailleur, of course you could try the old one.
I doubt that you need a new front shifter, all you really need is a friction shifter for the front. Does the old shifter actually have clickstops? If so, how many?
I would try it. You will need to lower the FD on the seat tube. If you have a problem it will likely be that the chain drops when shifting to the small ring. Triples have a deeper inside plate so if you get a new one be sure it will clear your middle ring when going to the big ring. For example, a 10 sp Ultegra made for a 39 tooth middle ring will not work well with a 9sp Ultegra crank with 42t middle ring. Don't ask....
a double fd doesn't have enough capacity to clear the chain on the small ring. it's just not long enough even if you lower it as far as you can. it also isn't designed to travel far enough in and out. just get a new fd. they're cheap anyway.
I would try it first since you've got nothing to lose. The profile of the triple vs double is only important if using indexed shifters. Capacity is the most likely problem, but there may be enough room, depending on the bike's geometry.