I'm interested in how I would choose a chainring configuration, supposing I was either replacing mine or building a new bike for a similar usage.
I have a 50/39/30 triple chainring (& 10-speed cassette) on my Bianchi Volpe. Rivendell sells a 46/36/24, with the argument that 50 is overkill, and if you're going to have a granny gear it should be smaller.
I buy that argument, but I spend 90% of my time riding 39 in the front and 15/17 in the back. If I downgraded my middle to 36, then I'd have to ride smaller cogs in the back, which means it'll wear faster (I do ~2500 miles per year of city riding). If I use the 46 then I'd be almost cross-chaining to get the same ratio.
So it sounds like this configuration would be bad for me.
However, I think a 46/30 double might be perfect. That would pull the big ring in closer so when I'm riding on the bigger cogs in the back I hopefully wouldn't be cross-chaining. It would wear slower because I'd be on more teeth. I do a moderate bike tour about once a year and the 30 has worked fine for me so far (haven't done any mountains, but have done some steepish hills).
Does my rationale make sense?