Triple RD compatible w/ compact
 

Hello

I inadvertantly bought a Shimano 6600 RD triple for a very good price. I overlooked the triple part.

I'm putting it on a cross bike with a compact double and 12-27 cassette.

Will it work or should I resell it?

Thanks much

It'll work fine.

Thanks Kevin (and I do like buying from Harris website)

What size chainrings are you using? If you're using 50/34T (vs. 50/36T), then the triple (GS) RD you have has the chain wrap capacity (37T) to allow you to run every gear combo (max 31T).

Assuming the chain length is set to be the shortest possible while still allowing the big-big combo, then the SS RD's chain wrap capacity (29T) falls short and wouldn't allow the use of the 34/12, 34/13, and possible 34/14 combinations. If you did go into these combos, then the RD wouldn't be able to tension the chain and the RD would fold into itself.

Some people will say you shouldn't use the above combos anyway, but they can be useful.

Thanks Jive, but now I'm confused. I have an FSA 50-34 chainring. Are you saying it will or will not work with that. The Shimano Ultegraa RD is a mid size cage

Sorry for the confusion. The GS (medium/long-cage) RD you have will work perfectly.

The length of the cage determines its chain wrap capacity. Basically, when you're in the big chainring/big cog combo, the chain is just long enough to handle that. But, when you're in the small/small combo, there's way more chain than is needed, so the RD has to take up all that slack. The longer the cage, the greater amount of slack it can take up; therefore, the greater difference in number of teeth between your big/big and small/small combos that the RD can handle.

Chainwrap = ([big chainring - big cog] + [small chainring - small cog])
Your chainwrap = ([50 - 34] + [27-12]) = 31

The SS RD can handle up to only 29, whereas the GS (your) RD can handle up to 37.

Thanks for the great info