Derailleur capacity question?

Seaneh

Hey lads.

I currently have a 105 rear mech with a 11-25 cassette + a 50/39/30 triple chain set.

Even with the 25/30 I'm finding the hills hard going while the panniers are loaded (probably because I'm a big lad, and I know that's pitiful) and I was thinking of bringing the bike back to something like it's original set up (11-32 cassette and a Dore LX rear mech).

But before I go to the bother of buying a new mech, I want to figure out what is the maximum capacity rear cassette I can use with my current set up?

I know that with a double/compact on the front I can use up to 30t cassettes on the back with my current 105 mech but I *think* that the triple chain set changes this and means that my cassette options are limited, from what I can figure out to, at the most, a 12-27 on the back.

So can any of your bike gods tell me how I figure out what setup I can potentially use without changing my derailleur?


Also, I'm pretty sure the 105 is medium cage, but not 100%.

smacl

This may be helpful;

http://bicycles.stackexchange.com/questions/7264/how-to-calculate-the-capacity-of-a-rear-derailleur

I run 53/42/30 with 13-28 cassette, but it is a long cage RD. Looking at the 5700 specs, it lists a capacity of 39 teeth or less and largest sprocket of 28t, which suggests you'd be fine on 28t sprocket, might be lucky with 30t, but unlikely to get away with 32t. That said, Canyon ship their AL with a default configuration of 50/34 cranks and 11/32 cassette.

Seaneh

I'm not sure which series my mech is (its older than 5700) but im guessing the capacity should be the same?

If so, 11-30 and 50-30 gives me a total capacity of 39t which is bang on the money?


edit:
I actually think it's old enough to be from when Shimano actually did 3 sizes in road derailluers because it looks longer than the new SS but shorter than the new GS road derailleurs, I might have to just bite the bullet and buy a mtb derailleur.

Poo.

cdaly_

I'm running 52/42/30 with 13-32t cassette. 105 medium cage mech. Sounds like you have the same mech. You'll need a slightly longer chain though.

Seaneh

Hmmm.... going by that I should be able to run an 11-32 (same total capacity as yours) with a medium so long as the chain is long enough?


This ish is confusing.