mobey1

Hi,

I have recently bought a Shimano Ultegra 6700 Chainset (Double chainring) 53/39t. In addition I have also managed to get a 6700 cassette off a mate which is 11/28... BUT i have no idea what size rear derailleur to go for. short, medium .... if someone could help me out here it would be much appreciated!

George

Steev

28 tooth is the maximum for a road short cage, so that will work as long as you don't for a still larger cog in the rear. Medium and long cages will also work.

mobey1

Great thanks for the quick reply!!!!

Panthers007

This is a true bargain for a real Ultegra rear-derailleur:

https://www.cambriabike.com/shopexd.a...EAR+DERAILLEUR

And it will easily work with a 11 - 28T cassette - despite Shimano's claim no larger than a 27T. Shimano tends to be very conservative for no good reason. These run fine on up to 30T. Some are using these on 32T - but that's pushing it IMHO.

Anywho, that's a $80 to $110 rear derailleur.

wrk101

+1 I bought one of those Cambria bike deals myself. And even if a short derailleur works, I don't see an advantage going with a short one. There is a lot more flexibility with medium or long cage derailleurs (who know next time you might want to go with a 11-28 cassette).

I bought the Cambria unit so I could make the swap to a 11/28 cassette myself. I just haven't gotten around to it yet.

+1 To comment below. Longer cage does not give you a larger rear cog, but it does allow for more chain wrap. So it give you more flexibility in managing front chain ring tooth differential and rear cassette differential.

well biked

Just to clarify.........all Shimano road derailleurs have an official largest cog compatibilty of 27t, as published by Shimano. This is for either cage length, it doesn't matter. The reason is that the cage length has nothing to do with the largest cog compatibilty (in regard to the upper pulley bumping into the largest cog on the cassette). In most cases, Shimano road derailleurs will actually work fine with largest cogs as large as 30t, as already stated.

In regard to the OP's specific drivetrain, the maximum chainwrap requirement (53 minus 39 plus 28 minus 11 equals 31) does exceed the official Shimano chainwrap capacity for their short cage road derailleurs (29t). In reality, a short cage Shimano road derailleur should work fine, as will the longer cage models.

Just keep in mind that largest cog compatibility and chain wrap capacity are two different things.

DaveSSS 

The specs for the new 6700 RD are a bit different than earlier models.

https://bike.shimano.com/publish/cont...SS.-type-.html

Panthers007

So is the price. If a 6500-series RD won't work on a 6700-series, I'm calling for a boycott of Shimano. That would be the same sort of stunt they used to pull. Until they were pelted with chairs, bottles, and tables when they took the stage at a trade convention in Los Angeles in 1982.

operator

You people need to understand how shimano comes up with their largest cog rating instead of blindly stating that it "usually" handles larger. The 27t figure you see bandied about here is a result of accomodating most derailleur hanger lengths. So people don't go omgwtfbbq when their derailleur at full max b-tension hits the larger cogs. If the bike has a shorter hanger than what shimano wrote that 27t rating for then it is possible for it NOT to work on a 27t or even a smaller sprocket. Reverse is true for longer.

Go read barnetts chapter 32 for the full on explanation.

well biked

Get over yourself, young man.

Panthers007

Good way to explain it. Thanks! Barnetts chapter 32? I have the full book on my HD. Perhaps I'll Copy & Paste job it. Shhh!

As an aside - I also have an Ultegra 6500-series RD on my road-bike. It has a 12 - 25T Miche cassette and 42 - 52T Campy Super Record (1982) crankset. Smooth and silent.

DaveSSS 

There are more polite ways to educate readers of the forum. Suffice it to say that a longer hanger permits the use of a larger cog.

Quite often, a manufacturer will simply list the maximum cog size and wrap capacity to match the range of product they sell. Campy has done that in the past. The wrap capacity of their short cage RD magically increased when compacts came out and the 50/34 added 2T of wrap, even though the cage length was not increased. Campy includes a drawing of the hanger dimensions suggested for their RDs. The length ranges from 24 to 28mm. See page 12 of the PDF:

https://www.campagnolo.com/repository...leur-11-09.pdf

FWIW, the hangers on my LOOK frames are all of 28mm in length, maybe 29.

Campy also introduced a 12-29 11 speed cassette for 2010. 2009 RD might work with the 12-29, but only if the hanger is over 28mm in length. Otherwise, a revised "B" screw mechanism must be installed. All 2010 RD have the change to handle the 12-29.

The wrap capacity is also affected by the chainstay length. The perfect length that requires close to an exact 52, 53 ,54.... inch chain will have 2T more wrap capacity than a length that requires a length ending in a .5 inch increment. Derailleur chains can only be sized in full inch increments.