Since I live and ride in NYC, I don't give any value to average speed. When I commute 10 miles to work it takes an hour on my MTB/Commuter, and it takes 59 minutes on my carbon road bike. It really doesn't make a difference that I can pound the road bike up the bridges and hills and hit 23mph on the flats, because these are all just quick bursts. Most of the time I'm approaching a red light, waiting at a red light, or accelerating from a red light. The time spent at red lights exceeds by far the time spent at green ones and moving.

Now, I also have a park loop that I can do where I never have to apply the brakes (also part of my commute). In the park, I've been able to maintain a 20mph AVERAGE speed based on my Cateye over 3 laps of 3.4 miles each. That's a pretty good speed and I always use this speed as a comparison to "internet" speed. I can hit 25 on the flat, 34 on the downhill, but the uphill of course slows me down. I've done the uphill at 21, but after doing that I may as well stop pedaling and call an ambulance. Usually a fast uphill is at 16-17, or a modest 14 if I'm just doing a casual run. When I see internet speeds of 20+ on the commute I know that's nonsense.

The fastest I ever rode though is during the Seattle to Portland double century. I did the first 100 miles in 4 hours 15 minutes. That's 23.5 mph average, no stopping. I was in a non-stop paceline where I never managed to find the front. I completed the entire ride in just over 10 hours.