I just got a Salsa 42 inner chainring. There is less chain rub than with the 39. With the 39, the chain would rub the large chainring with the 1,2, and 3 smallest cogs. Now, with the 42, it only rubs with the 1 and 2 smallest cogs. I also got some chainring spacers (.6mm) which I haven't used yet. They are female spacers. Now the question is: Should I move the inner ring in, or the outer ring out? It is possible to do either.