Good info here. I've only been seriously biking since last fall and had been wondering how to get my speed up. I do a lot of 50-75 mile rides, but my speed is generally only right around 13.5 mph. I then realized that I'm never really pushing myself to go fast, so I started doing interval training. I've really only been working at it for about a week, but I've already managed a 30 mile ride averaging 16 mph and I've definitely been spending more time at much higher speeds. That's still not great, even considering my clunky hybrid, but I know I'll get better.