bobby c

Hi - I been using a 12-25 rear cassette the last couple of years but for a couple of hilly centuries, I purchased a 12-27 to use when needed. I have an extra rear wheel so I've two wheels I can use as needed. Currently, my chain (new) is setup (per Sheldon's method) for the 12-25. I used the 12-27 for the first time this weekend without adding any links - I can cross chain big-big (though I don't ride that combo) but it is a stretch. In my ideal world, I'd love to use 1 chain for either wheel setup. So my question - is this advisable? As I see it, I have 3 choices:

1. One chain - set ideally for the 12-25. When using the 12-27, the chain gets tight on the big-big combo that I don't use.

2. One chain - set ideally for the 12-27. In this case, the chain would probably have a lot of slack in the little-little combo, again, not something I would use (though it could happen).

3. Forgetaboutit. Different chain for for different cassettes.

What's your suggestion on what to do?

Thanks,
Bob

edzo

well, easy. get a new rear derailleur with a longer cage, and run a chain that fits the 12-27 big-big

it should suck up the slack if there is any when running the 27-big big chain on your small small

bfromcolo

This is the one. Since both cassettes have a 12 small cog the amount of slack if any is the same running small-small. If there is slack you would need a rear derailler with a higher capacity, but I think most deraillers would handle either fine.

urbanknight

There should be enough to accommodate both with a standard derailleur, but if it came down to it I'd say #2

Adohrn

1. One chain - set ideally for the 12-25. When using the 12-27, the chain gets tight on the big-big combo that I don't use.

This one is a definite no. Go big-big and step on the gas, and watch the derailler crash into the spokes. Possible outcome toasted frame, derailler, wheel or you. Running with to tight a chain leaves the possibility of costly mistakes.

tsl

This is the combo I've been using on two different bikes for quite some time now. I've had no chain slack issues either, since all cassettes in use are within the capacity of their respective RDs.

A issue I have had is making sure the cassettes are in the same position on each wheel. A little off and shifting problems result. Nothing major, but not as smooth. I've had to tinker a bit and discovered it was brand related. As long as I use the same brand of cassette on the wheels for each bike, I can switch wheels with impunity. If I mix brands (say, Shimano and Nashbar) I have to adjust the RD's "L" screw and mess with cable tension.

DMF 

Either 2 or 3, depending on the condition of the cassettes and chain(s).

But really 4. There's not much difference between a 12-25 and a 12-27. I frequently swap between a 11-23, 12-25, as 12-27 with the same chain with a long-cage RD. And between 12-25 and 12-27 on a short cage (not that the 11-23 won't work as well, rather that I haven't tried it).

Bill Kapaun

I'd set the chain for the 27T cog. Mistakes sometimes happen!
The fact you don't intend to use the big:big combo is compensated by the fact you shouldn't be using small:small either. That pretty much eliminates at least 1/2 of the potential chain "sag" issue.

Al1943

There should not be any problem with this at all. There is not a one link difference between the two setups. I alternate between 12-23 and 13-27 on various wheels with no problems and no adjustments (D-A road derailleurs).
What do you mean the derailleur gets tight on the big to big combination. It is very important that the derailleur does not reach it's forward limit of travel in the big to big combination. If it does then the chain is too short, add one full link (1 inch).

Al