Short Cage vs Long Cage Derailleurs

[Chuck Hammer]

When would you use one or the other?
For a 10 speed 6600 Ultegra double set up.
Thanks!

[christian]

Short cage wraps less chain (smaller "capacity), so you would use it for a double. A long cage wraps more chain, so you'd use it when using wider gearing, i.e. a triple.

To calculate required chain-wrap, use the following formula:
(Big Ring - smallest Ring) + (biggest sprocket - smallest sprocket) = wrap.

So a 53-39 combined with an 11-21 has 24 teeth of wrap required, and a 50-40-30 with an 12-34 has 42 teeth of wrap required. The "capacity" of the derailleur is usually listed in the materials which accompany it.

You can use a long-cage derailleur at all times, but a short-cage derailleur will shift (marginally) faster.

[Chuck Hammer]

The bike (Fierte steel) has an Ultegra Triple set up on it we are converting to a Double and have the double shifters and double FD and Crank. So I could use the existing Derailleur?

[weiwentg]

The bike (Fierte steel) has an Ultegra Triple set up on it we are converting to a Double and have the double shifters and double FD and Crank. So I could use the existing Derailleur?

sounds like you've got an Ultegra long cage on right now, and if so, yes. I've used a long cage on a double setup before, worked fine.

[Ralph]

RD's come in short, med, and long. What some call long is really medium. So it's important to be clear about what you call "long".

[christian]

Yes, definitely.

The only downsides are (extremely minor) additional weight from the longer cage, and (I believe wholly theoretical, but at the minimum unnoticeably) slower shifting than a short cage derailleur might offer.

I sort of can't believe I would even list those downsides, as they are so minor, and, in the case of the latter, maybe not even real, but if I didn't, I figured someone else would.

But in short, yes, rock on with your current rear derailleur.

[christian]

RD's come in short, med, and long. What some call long is really medium. So it's important to be clear about what you call "long".Not in this case. Either a long or medium cage will have more than enough wrap for the proposed double drivetrain.

[Chuck Hammer]

Thanks everyone.... just saved a couple of bucks which can go towards some other items needed for this bike