I recently switched to 165 crankarms (from 172.5); stayed with the standard 53/39 chainring up front; and using a 12-25 cassette. I'm on the shorter side (5' 6"), and from what I had read and researched, that sounded like it might be a good move to make (slight improvement to aero, combined with little more breathing space to stay in aero, etc.). Pretty happy with the change so far, although I admit to being a little surprised at just how much difference that 7mm makes to my effort in the same gears. Haven't run out of gears going uphill yet, but definitely have to use the bigger (size) gears in the back more often.

I'm going to be doing IM Chattanooga in September, and thinking I may get an 11-28 cassette to provide a full range of options, wanted to get some thoughts on that; as well as the possibility of switching the chainrings to a 52/36 or 50/34. I've searched the forum and read through a number of threads, as well as the related links. The whole thing is making my head spin a bit, to be honest. Assuming that I want to stick with 165 crankarms, trying to figure out how that matches up with the chainring and cassette selections to provide the optimal combination.

One quick example to provide a real-world scenario; we have a couple local hills where the elevation increases a little over 150 ft in just under a mile. At the end of my long (80-90+) mile rides; I'm now going to the 39/25 combo to get up the hill at a nice steady pace. Makes me slightly nervous that the same setup at the end of IM Choo would have me struggling more than I want, leaving me too fatigued to have a good run.