I live at sea level, but sometimes ride in the mountains up to 12,000 above sea level....riding is ok, you lose about 25% of your power at 12,000, so bring low enough gears and keep track of your pulse and hydration. Sleeping above 5000 feet is hard for me, i wake up with mild AMS....just a little low on O2 in the blood. Mt Lemmon is a nice climb, I did it 25 years ago just after they had torn up the road....miles of dirt and gravel....pretty up on top