Joe Gilmore asked:
>
>>My LBS installed a "double" (short, not long cage) rear deraileur on a bike with a triple
>>crankset. They said it doesn't matter,
>>I've asked them to replace with a "triple" rear deraileur but I don't want to be "hardnosed" if it
>>really doesn't matter. Does it matter?
Someone who wanted to be helpful overstated:
> Of course it matters. No way will that double derailleur have enough capacity for a triple. In the
> granny ring, most cogs will be unusable,
"Most cogs" _shouldn't_ be used with the granny ring, so if you have good shifting habits, it
won't matter.
> and you are likely to throw a chain.
I don't believe ther's any greater risk of throwing the chain. Worst case is that if he accidentally
shifts into one of the smaller rear cogs while on the granny ring, the chain will droop.
> Or, even worse, if the chain is so short that that doesn't happen, you will not be able to shift
> into the largest cogs in the big ring. Mistakes happen, and you will eventually shift where you
> are not supposed to, and break something.
Certainly nobody should ride with a chain that is too short, but that has nothing to do with
derailer choice.
I would say, as a general rule, that if you _need_ a new derailer, you might as well get a
long-cage one if you have a triple chainring, but I commonly do upgrades where I convert doubles to
triples, and leave the original short cage derailer, if the customer isn't going to a seriously low
gear in back.
Indeed, my Hetchins is running a current-model Dura-Ace rear derailer with a 12-28 cassette and a
50-28 chainset, works fine for me. (I don't use the 28 in front with any of the smaller rear
sprockets, though.)
Sheldon "It Works" Brown +-----------------------------------------------------------+
| Always listen to the experts. | They'll tell you what can't be done, and why. | Then do it.
| --Robert A. Heinlein |
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Massachusetts Phone 617-244-9772 FAX 617-244-1041
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