I just bought a new bike and thought it had a 39T small chainring instead of the 42T that it really has (Ultegra SG). I want to put a 39T on since I'm always climbing hills but when I've searched for a 39 it says match it to a 52 or 53B and my large ring is stamped "A-53" (the small ring is stamped "A-42").

Does anyone know if a standard Ultegra SG 39T ring (130mm spacing) will fit with the "A-53" ring?

Also, for climbing, I'm thinking of getting a 12-27 cassette. Is the gear ratio difference between a 42T and 39T more or less than the difference between a 23 and 27 (in the rear)? It could be that I'll be fine with the 23 in the rear if the 39T ring makes a significant difference.

Thanks for any help.

:confused: