Bicycle Mechanics - Top swing bottom swing front derailleurs
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09-10-11, 03:43 PM
The last time I searched for this, I got a trojan horse from socalriders.org. Anyway, I would like to know, if you have a Nashbar touring frame and Shimano STX-RC MC41 rapidfire shifters, would it take either a top swing or bottom swing front derailleur? I can't even understand the explanation on the sheldon brown website.
And what in the world is a Shimano FD-MC17? I looked at this site: http://datenbanken.freepage.de/traut/SHIMANO.html and can't even find it. Well, I looked but didn't see it. Is it really Deore? Does anyone know if it's compatible with an 8 speed setup?
FDs can be either top pull or bottom pull, which relates to the direction they expect to receive the cable from. Traditionally, road bikes use bottom pull(cable rounding BB shell before hooking on to the FD) while MTB's use top pull,to get the cable away from dirt and crud.
Also used to be that the seat tube clamp always was above the cage - top swing I'd presume. But there's also a design where the clamp is lower - almost mid-cage. But this is mainly an aesthetic issue, and some compatibility issues if you want to run water bottles on the seat tube. Pull direction and shifter compatibility is more important.
09-10-11, 06:15 PM
Cool, I just found a link with info...
"I'm convinced that the simple, dated, ugly bottom swing design is superior in that it puts up with more abuse. It seems that top swing derailleurs are here out of necessity, to address the needs of crowded full suspension frames."
That's something I wanted to read.
EDIT: Well, this is silly. I just found a contradicting message:
"As with so many things, you can theorize one way or the other as to which design should be better etc. The reality is that there is no substitute for real world testing. In close to 20 years of biking, including 2 years as a shop mechanic, I can say that low clamp derailleurs almost unequivocally shift better than the high clap versions."
09-10-11, 10:03 PM
FD's don't wear out that often and they are usually dirt cheap. The more important things to consider are top pull/bottom pull (where the cable comes from), clamp size (or braze on), throw and cage shape (triple or double), mtb or road cable pull (Shimano mtb FD's pull a different amount of cable per shift than their road FD's). I've built a bunch of Frankenbike's over the years and the FD is surprisingly hard to get right. There are lots of variations that can't be fudged and have to be right. IMO, the only difference between top swing and bottom swing is whether or not it will fit above the BB shell and whether or not it will interfere with a bottle cage on the seat tube.
09-10-11, 10:58 PM
Yeah, thanks for the above comments. Does anyone think I made a bit of a risk by getting a FD designed for 26/36/46 and use it with a 24/34/42 crankset instead? I figured 46 maybe is the closest I could get to 42 if I couldn't find a 42 of a same quality level.
I do know however that it's a triple, made for a mountain bike shifter (cable pull), 31.8mm for my Nashbar frame and is bottom pull.
Also, does anyone think that if I bought a FD intended for a 7 speed cassette that there would be any chance of an 8 speed chain rubbing against the sides with an 8 speed cassette. My thinking is that an 8 speed cassette would make the chain go at wider angles hence the possibility the chain might rub against the front derailleur. I took the chance partly because I know a 7 and 8 speed chain are the same width.
Does anyone think I made a bit of a risk by getting a FD designed for 26/36/46 and use it with a 24/34/42 crankset instead?
No. I've run a sestup like that for a year now w/o issues
...Also, does anyone think that if I bought a FD intended for a 7 speed cassette that there would be any chance of an 8 speed chain rubbing against the sides with an 8 speed cassette.
I've never measured the inside cage width of different FDs, but my gut reaction is that if it's aproblem, it'll occur at cross-chaining, which you shouldn't be doing in the first place.
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