Long cage, short cage.

[Billy Wizz]

Can someone explain the difference, advantages of this option on Shimano rear derailliers, ?

 

[raleighnut]

Long cage simply has a bigger tooth capacity allowing a wider range of gearing (needed with a triple up front)

 

[screenman]

A long cage will cope with wider ratio's. Or in simple terms take up more slack.

 

[Ajax Bay]

Rear derailleurs (RD) usually have both a largest sprocket (which is generally hard to exceed although some people have 'work-arounds') and a capacity listed. Both these limits are expressed in 'teeth'.
Capacity = (biggest chainring - smallest chainring) + (biggest sprocket - smallest sprocket)

eg:
Shimano Sora 9 Speed Rear Derailleur
37 tooth total capacity, rear sprocket size range 11-32T (Short Cage)
41 tooth total capacity, rear sprocket size range 11-32T (Long Cage)
Look at an example with, say, a 9-speed cassette of 12-13-14-15-17-19-21-24-27 and using a compact 50-34 chainset. Normal calculation requires a cage where the capacity = (50-34) + (27-12) . . . = 16+15=31 teeth - SS is fine. But if you use a triple eg 52-42-30 and a 11-28 cassette then the capacity you need is 22+17 and you'd need a GS RD as the capacity required is 39.

So with a compact unless you have a huge (ie bigger than 32) largest sprocket, the SS short cage is 'always' ok (and there is no benefit getting a GS, just in case).

 

[Billy Wizz]

Rear derailleurs (RD) usually have both a largest sprocket (which is generally hard to exceed although some people have 'work-arounds') and a capacity listed. Both these limits are expressed in 'teeth'.
Capacity = (biggest chainring - smallest chainring) + (biggest sprocket - smallest sprocket)

eg:
Shimano Sora 9 Speed Rear Derailleur
37 tooth total capacity, rear sprocket size range 11-32T (Short Cage)
41 tooth total capacity, rear sprocket size range 11-32T (Long Cage)
Look at an example with, say, a 9-speed cassette of 12-13-14-15-17-19-21-24-27 and using a compact 50-34 chainset. Normal calculation requires a cage where the capacity = (50-34) + (27-12) . . . = 16+15=31 teeth - SS is fine. But if you use a triple eg 52-42-30 and a 11-28 cassette then the capacity you need is 22+17 and you'd need a GS RD as the capacity required is 39.

So with a compact unless you have a huge (ie bigger than 32) largest sprocket, the SS short cage is 'always' ok (and there is no benefit getting a GS, just in case).

Thanks for the detailed information, Ajax Bay, I have the GS, I have never been one for looking into the ins and outs of the engineering of these things, always just rode the hell out of them and when there broke take them back to the shop.

But as I get older the tinkering has started again, I used to build and race motorcycles but much prefer the, I won't say safer option, the hills in Wales are still a buzz.
Thanks.