Hey everyone, Im new to bikes, Im looking at purchasing a trek 3700 or 3900, I was just browsing through bikes and Im wondering what the crankset numbers mean.....for example on the Trek 3900 Crank: SR 42/34/24 ..... I cant find any solid answer to what these numbers are, Im thinking it could be the diameter in mm of the 3 chain gears on the crank?