The bikes don't make much difference. I wish they did. When I was in my mid thirty's my average speed on a fast solo ride was about 19 or 20. But now, thirty years later, with a twenty year gap in my riding, I'm pretty sure I'll never average those speeds again. So now I mostly ride touring bikes on 1-1/4" tires, for comfort, with no cycle computer to track speed and remind me how much slower I am. I do try to keep track of my time, though, and sometimes calculate my average speed when I get home. I've tried hard this spring & summer to improve my speed/ time for my typical 28 mile ride, but I've seemed to sort of level off at about 15 or 16 mph average, roughly.