Originally Posted by genejockey

Yesterday's ride was weird. I felt like I was working fairly hard, and my HR confirms it, but my average speed was really slow - 15.9 mph, the very slowest I'd ever ridden this route. I was riding Mrs. Peel, on which I had just mounted the clincher wheels with Michelin Dynamic Classic tires, instead of the tubular wheels with Conti Giros. I went back and checked the last time I'd ridden this route on Mrs. Peel, and with much the same HR average and max, but with an average speed of 16.7 mph. AND that ride I describes as "Z2 recovery", whereas this one I felt like I was working hard a lot of the time.

So, I swapped the tubular wheels back on for today's ride. We'll see how it goes. I find it hard to believe the tires could make THAT much difference without being flat.