Derailleur help please: SS or GS

MattC59

Right then, this may well be a dumb question, but here we go, feet first..............

I'm building a new bike, on the front there will be a 50-34 compact and on the back (probably) an 11-28 cassette, as I want to keep roughly the same spread of gears that I have with the 52-39-30 / 12-27 triple that is on my current bike.

Do I go for the Ultegra 6700 SS rear mech, or the Ultegra 6700 GS rear mech ?

The capacity of the SS is 33T, although I'm not quite sure what this refers to. (That's where the question may have got a little dumb, considering my 30-odd years of riding bikes ! :oops: ).

So, what is does the 33T capacity signify, and will it be ok with the gears mentioned ?

Cheers........... Matt

smidsy

According to United Bicycle Institute:

Determine Maximum Chainring Difference by subracting the number of teeth in the smallest chainring from the number of teeth in the largest chainring

Determine Maximum Cassette Cog Difference by subtracting the number of teeth on the smallest cassette cog from the number of teeth on the largest cassette cog

Determine Total Drivetrain Capacity by adding Maximum Chainring Difference to the Maximum Cassette Cog Difference

Record the Maximum Cassette Cog (the number of teeth on the largest Cassette Cog)

For Shimano:

SS - Short Cage Road Double - Maximum Cassette Cog is 27 and Total Capacity is 29

GS - Medium Cage MTB/Road Triple - Maximum Cassette Cog is 34(MTB)/27(Road) and Total Capacity is 33(MTB)/37(Road)

SGS - Long MTB - Maximum Cassette Cog is 34 and Total Capacity is 45

MattC59

smidsy wrote:

Isn't it the difference between the big ring and the little ring teeth? - defining what cassette combo will work for that mech.

I don't know as it is. The Shimano website states:

Maximum Sprocket 28T
Minimum Sprocket 11T
Maximum Front Difference 16T
Total Capacity 33T

Back in the mists of time, I knew this sort of thing, but can't for the life of me remember what it is (turns out that's what happens when you turn 40 !! :roll: )

smidsy

Ive now edited my post with some technobable which confirms (sort of) my original stance.

So 50-34 =16 and 28-11=17 giving a total of 33 which is exactly what you need

MattC59

WooHoo............ excellent
(the SS looks better than the GS :roll: )

Cleat Eastwood

i have exactly that set up 50-34 and 11-28 with an ultegra GS rear mech - i thought i'd play safe even though I came across this when researching it- from wiggle

"You need the RD-6700-SS. The GS (long cage) is only necessary when running a front triple.

There is advice on here that suggests you must use the long cage for an 11-28. This is incorrect. The RD-6700-SS was specifically engineered to accommodate using a compact crank and an 11-28."

The ss will be fine

MattC59

Cleat Eastwood wrote:

i have exactly that set up 50-34 and 11-28 with an ultegra GS rear mech - i thought i'd play safe even though I came across this when researching it- from wiggle

"You need the RD-6700-SS. The GS (long cage) is only necessary when running a front triple.

There is advice on here that suggests you must use the long cage for an 11-28. This is incorrect. The RD-6700-SS was specifically engineered to accommodate using a compact crank and an 11-28."

The ss will be fine

Thanks Cleat, but that's enough about your sex life !!!

yaya

I run a 50-34 chainset with a 11-28 cassette and a short cage 6700 mech. One thing to be careful with is the chain length. If you are in the big ring and go to the larger 3 cogs, the cage tends to sit almost horizontal which can brake the cage (been there, done that) so add a couple of links to give it a bit more play