I never even look at my computer's mph. The average it shows is much lower than my usual cruising speed. Given that I live in NYC, with all the traffic and lights, average speed is pretty meaningless. When I was training about 5 years ago now, I was able to average, by my computer, over 20mph doing non-stop loops of Prospect Park, over about 15 miles. This was with resetting the computer when I arrived in the park and already rolling. This was also solo riding. That is a VERY difficult pace to maintain for an average rider. A fit rider like myself at the time could do it, but NEVER on the streets. That's suicide. I can no longer maintain that pace even though I continue to ride (I'm 56 now, so not so young anymore).