Originally Posted by
tarwheel
Just curious ... are there any hills where you ride? Although I would agree that rolling resistance is a big factor, tire weight is also important when going uphill. We have nothing but hills in western and central NC, and I have no doubt that heavier tires are slower and more difficult to ride uphill. I've got 5 road bikes with tires ranging from 23 - 35 mm (all folders), and the bikes with larger, heavier tires are simply slower going uphill. The larger tires roll nice on flat terrain but will give you a workout when you hit the hills.
There are (what I consider) lots of hills where I ride.
When riding up a hill at a constant speed, additional weight of wheels is equivalent to additional weight anywhere on the bike/rider. So I'm not sure how to explain your experiences (except that on flat land, your biggest resistance is probably going to be air resistance and when your climbing hills, you're now in a regime where rolling resistance becomes more important).