Originally Posted by
Road Fan
Assuming the route is a loop, I would discount wind and altitude, at least as gross factors.
Yesterday I rode a route I do quite often. My average on this course, in general, is about 13.5-14.5 mph as a portion of it is in the City where I am constantly slowing for traffic, signs and lights. Yesterday was windy, more than usual, and there were some pretty high gusts at the start. From the start I was into the headwind and the gust and It was brutal at times. By the time I reached the turn around point the winds started to diminish and shortly after they subsided.
So for the 1st half I was into a headwind with strong gusts and for the 2nd half I didn't get the benefit of a tailwind. Bummer for me but at the end my average speed was quite a bit lower and I came in at 11.6 mph..
I don't think you can completely discount wind based on my experience as the wind strength and direction can change, sometimes drastically, on the ride as this was my experience yesterday.