Originally Posted by Machka

Seems to me that's not actually true, according to a study a few years ago.

Originally Posted by Wikipedia

The primary cause of rolling resistance is hysteresis:

A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance and is attributed to the viscoelastic characteristics of the rubber.

-- National Academy of Sciences[3]

Thus materials that flex more and bounce back slowly, such as rubber, exhibit more rolling resistance than materials that flex less, such as steel, or that bounce back more quickly, such as silica. Low rolling resistance tires typically incorporate silica in place of carbon black in their tread compounds to reduce low-frequency hysteresis without compromising traction.[4]