I was thinking about this on my ride today. We headed out for a "slow" ride, as it was 88 and the humidity is climbing. And, it was close to noon. I just wanted to get in 15 miles, as I am sorely behind on my mileage for the year. The slow went out the window when a guy riding a mountain bike on the road, latched on behind me, after we passed him. I told DH to kick it up. Finally, we pulled off, at an ice cream place (no, not to eat), to get him off of my rear, as I couldn't maintain a 20 mph pace in the heat, for more than 2-3 miles.
After dousing myself with water and drinking copious amounts, we continued on, and by that time, on the easier side of the loop. All of a sudden, we had picked up the pace again, so that when we got back to my neighborhood, before the hill climb, my average was just under 16 . Now, I know that's not much for some, but for me, on any day it is. When I got home, my face was so red, I thought I had forgotten to put sunblock on. I felt fine, but it took a cool shower and 1.5 hours to go away.