mtnbud, Before I simplified my cycling life to just three bikes I had several road bikes with crank arms ranging from 165 mm to 175 mm. For me just a few minutes riding was all that I needed to be comfortable. My favorite size is 172.5 simply because it bridges the torque/cadence issues between the 170 mm and the 175 mm crank arms. At this time my road and touring bikes have 170 mm crankarms and the mountain bike has 175 mm crankarms, FWIW.

Brad