@OP: so, which is it -- 47c or 37c? If the latter is correct, then for a 170lb load (thanks, Sheldon Brown) simply try 60 rear/50 front -- could even go slightly lower given your weight if riding the bike unloaded. I've used SB's suggested pressures for years/never had a problem, and never found an advantage in going above or below. Just sayin'; it's easy to over-think this stuff.