If you’ve been shopping for new tires in the past decade–or even perused the window sticker of a new car–you’ve likely come across the term “low rolling resistance.” Maybe the tires in question carry “green” or “eco-friendly” labels. That’s because these special tires require less effort to roll down the road than regular tires. This means your gasoline engine or electric motor work less and thus your vehicle delivers better fuel economy or your electric car has greater range.
How much of an improvement are we talking about? A 2016 study published by the University of Michigan compared 49 tire models in a common size. It found that tires with the highest rolling resistance led to a 6.3-percent greater fuel consumption than those with the lowest.
The U.S. Department of Energy says installing low rolling resistance tires should improve fuel economy by about 3 percent. But keep in mind that any set of new tires likely produces an initial drop in fuel economy. New tires have yet to wear down, which in itself reduces rolling resistance, although at the expense of safety.
Tires are made primarily from rubber, so they can bend and stretch as they roll. But as the engine turns the wheels, some of this energy gets wasted. When the tire flexes and rebounds that energy is converted to heat, a process called hysteresis.
Modern rubber compounds used in low rolling resistance tires better resist hysteresis. They snap back with less energy loss. The magic ingredient in these new formulations? Silica, commonly known as sand.
An oft-repeated concern with low rolling resistance tires is that they won’t grip as well as standard tires. But the science behind new rubber compounds insures that stiffness and resistance to hysteresis doesn’t compromise the softness and elasticity necessary to conform to the road.
Tire engineers take advantage of the different frequencies with which a tire bends. Rotational motion creates low frequency stresses, while the rough road surface under the tire creates a high frequency series of deformations. Rubber compounds in low rolling resistance tires are engineered to be stiff during the former and soft in the latter.
Once the exclusive province of hybrids and other high-efficiency models, early fuel-miser tires rode hard and didn’t grip so well. Today’s low rolling resistance tires force no such trade-offs. With specialized tread patterns and sidewall construction, and state of the art rubber chemistry, low rolling resistance tires have gone mainstream.