It varies widely depending on the road conditions, my physical condition at the time, and who I am riding with. On flat roads with no headwind and a group of three we sometimes managed 18-22 mph for an hour or two of pace line riding when we were on the Trans America. In the Sierras last year there were sections of steep climbing where I wasn't much faster than a walking pace. It is hard to pin it down to an average, but generally I am somewhere in between those extremes.