Altitude was a factor for me, but I live at sea level, so standing on a chair is elevation to me. Markleeville (Where the DR starts and finishes) is about 5500 feet. We rode three passes, Monitor Pass is 8,314', Ebbetts Pass is 8,730' and Carson Pass is 8,652. Not particularly high, but for me it was an issue. Some guys I know arrive as much as a week early to ride and acclimate, I have to work so I went up Friday, day before the ride, and rode just a bit. Biking up to 14,000 would be impossible for me...