Originally Posted by
prathmann
Yes, when you're riding you do slightly accelerate the bike with each downstroke and there's a slight deceleration in between. The extra weight of a heavy tire makes it a bit harder to do the acceleration. But the energy you put into it isn't lost since the spinning tire now acts as a flywheel and helps keep the speed up in between the downstrokes. So with light wheels/tires you'll get more speed variation during the course of a full pedal cycle while the flywheel effect of heavy wheels/tires will keep the speed more even. On level ground and assuming both air and rolling resistance are unchanged the average speed will be essentially unchanged. But, as mentioned, heavy tires tend to have more rolling resistance due to thicker tread and stiffer sidewalls that lose energy when the tire is compressed near the contact patch.
Aside from the fact that a heavy tire connected to the drivetrain via a freewheel cannot return energy to the drivetrain, is by definition (unlike a fixed gear) NOT a flywheel, I can understand what you're saying in terms of angular momentum (and the propensity of heavy tires to conserve it). I'm not looking for a thermodynamic free lunch, though, so I'm content to conserve energy in my much more frequent acceleration needs, and am therefore far more enamored of lightness than I am of weighty wheels that coast longer (and require more force to slow). I just don't consider that a benefit in any case, and especially in light of the penalties. When I ride, I rarely coast, and apparently that colors my tire preferences.