I find that true as well. Before riding I did running and its the same there too. Our cross country coach would have us do a two mile warm up followed by 110 yard sprints. Then after a while, that became too easy and the body wanted to warm up even more before the race. I also notice that in running, you reach a higher heart rate faster than the same time on a bike. So if you want to warm up, just run for 10-15 minutes before the ride. This will save you time off that 40 minutes.

It would be interesting to find out how many bike riders used to run and how many have never run at all. I'm talking about the running that takes you 10 miles or so each time. I think distance running complements road riding.