which cage ?

[snoged]

just looking for advice please
my setup is 53/39 front and 11/27 rear and a shimano 105 rear mech with a short cage(I think) and this is the problem which rear mech will cope with that gearing ?
many many thanks for advice regarding this

 

[Smurfy]

This is a bit old, but I think it's still correct.

In selecting a rear dérailleur, the first consideration is how wide of a gear range it will be required to shift. Most 10-speeds have the same high gear (52 teeth on the front with 14 on the rear). The major difference between types of gearing is in how low the lowest gear is and what kind of spacing is used in between.
Dérailleurs usually are rated in terms of "tooth-difference capacity," a number that represents the dérailleur's capacity to take up slack in the chain. To find the minimum tooth-difference capacity needed for the gearing you have selected, subtract the number of teeth on your smallest rear sprocket from the number of teeth on the largest. Do the same for the front sprockets, and add the two numbers. For example, if your rear sprockets run from 14 to 26 teeth, the rear difference is 12. If your chainwheels are 36-52, the front difference is 16. Adding the figures for front and rear, we get a total difference of 28 teeth. If you get a dérailleur with a 28-tooth capacity or more, it should handle the range. If you use a dérailleur with insufficient tooth difference capacity, the chain will be too slack in some gears or too tight in others and you probably will not be able to get it to shift properly.

You will be able to find the maximum tooth difference for your rear mech model by checking the technical sheet on the Shimano website. The model number will be stamped on the back of the parallelogram mechanism, it will be a format something like RD-XXXX, where XXXX are four numbers. When you've got that, go to the Shimano website link above, click on 'road bike', then '105', then click on the document for your model of rear mech, which will be a link starting with SI-5.

 

[Smurfy]

Here's an example for you:

The RD-5500 and RD-5501 rear mechs can cope with a total tooth capacity of 29T in the SS cage version, or 37T in the GS cage version. In the specifications it also states the maximum and minimum permissible sprocket sizes.

 

[snoged]

that's great info many many thanks for youre help !