what size rear mech

radiation man

if i have a 50- 34 compact chainset and a 34 - 11 or 32-11 rear mech what size shimano ultegra rear mech will i need.

freezing77

radiation man wrote:

if i have a 50- 34 compact chainset and a 34 - 11 or 32-11 rear mech what size shimano ultegra rear mech will i need.

Depends on the rear triangle and derailleur hanger geometry.
Wide gear ratio compatible up to 28T (SS)
Wide gear ratio compatible up to 32T (GS)

GS Medium 32T Max , but depends as above.

rafletcher

Look at the tech docs (just google shimano tech doc 6700 rear, I did).

http://techdocs.shimano.com/media/techd ... 702204.PDF

You'll see that BOTH 6700 SS and GS mechs have a max sprocket of 28T. You could probably run a 30T, but 34T I would worry about jamming the top jockey wheel into the cassette.

The difference is in the total capacity - 33 for SS vs 39 for GS. The GS is meant to be used for triple chainsets so you can have 22T difference between largest and smallest chainrings (30 to 52)

So if you run 50/34 at the front that's 16T, and the SS is fine - BUT you can't run the 34T sprocket on yr cassette with either.

For that you'll need a touring mech I'd guess - maybe a Tourney.

bendertherobot

radiation man wrote:

if i have a 50- 34 compact chainset and a 34 - 11 or 32-11 rear mech what size shimano ultegra rear mech will i need.

I take it you mean cassette. If you mean rear mech the answer is, the same one.

Not sure about long cage shimano. For this sort of thing, and I appreciate you won't want to change, SRAM is the way to go.

bendertherobot

I should also add that 30T really is a good enough gear. Enough to make a difference on a 28. It would be "nice" to have more for those really rare nasty hills, but it could be overkill.