How it’s tested
To measure rolling resistance, Wheel Energy presses a tire against a smooth, nearly cylindrical metal drum and turns the wheel with a specific amount of power, then measures the speed of the wheel. All other variables are controlled so rolling resistance between the tire and the drum is the only thing affecting wheel speed. Measuring that speed allows Wheel Energy to calculate the coefficient of rolling resistance of various tires.
It was long assumed that narrow tires have less rolling resistance than wide tires, but that is in fact not true—Wheel Energy found that a 25c tire has 5 percent less rolling resistance than an identically constructed 23c tire. Many people also believe that a tire’s casing—the structural foundation of the tire—made with finer threads creates less resistance than one constructed with thicker threads. This is also incorrect.
From the lab to the road
Rolling resistance is arguably the most important characteristic of a triathlon race tire since it directly affects straight-line speed. To reduce rolling resistance, Specialized removed material from the shoulder of the tires, changed the tread and rubber composition and reduced the casing rubber thickness. Through these changes, Specialized was able to reduce the rolling resistance of the S-Works Turbo by an astonishing 25 percent compared to their top-flight tire from 2010. According to Specialized, it is competitive with the fastest tires from any other brand.