When I moved to Colorado from Illinois my bike had a low gear of 30/25 (triple with 14~25 cassette). What works a 700ft on flat terrain is torture out here. I went on an 82 mile ride with three passes, one at 11.3kft and two at ~10.5kft, 6000ft of vertical climbing. I was running a 28/28 and it wasn't low enough for me. I've since upgraded to a 24 front ring and it's ok now. The last pass, Vail in the afternoon is a killer, you can actually see the trail next to I-70 on the south side as you climb from the west.