I live at about 180 ft. above sea-level, and was wondering about the same thing until I went to Colorado last week. Crossed three passes at 12,000 ft., and did a lot of riding at 10,000. The bike ran perfectly, and by looking at the exhaust, it looked like it was running more lean than at home. Almost like it slightly overcompensated for the altitude. Power was definitley down at 12,000 ft., (no first gear power wheelies)!