Hmm, with a fat seat tube (sounds like an aluminum frame) I would play safe and go for 113. The front mech otherwise not be able to shift onto the inner chain ring.
It is actually a steel frame, but I think I will go for the 113 anyway as just seems to me like the safer option. Thanks for your responses though, it's much appreciated.
Specialized Crossroads Comp Hybrid 2005 (being butchered for parts)
Trek Y3 1998, Trek 930 Single Track XC 1997
Saracen Rufftrax 1996
Giant Box Two 1998
Marin Bear Valley 1988
Parkpre Team 925 1994, Parkpre Comp Limited 1994