In the latter two cases, the effect of air resistance must be subtracted or the tests performed at very low speeds. These coefficients are measured on rollers, with power meters on road surfaces, or with coast-down tests. In the case of bicycle tires, values of 0.0025 to 0.005 are achieved. When measured by using these standard test practices, most new passenger tires have reported RRCs ranging from 0.007 to 0.014. These tests ( SAE J1269 and SAE J2452) are usually performed on new tires. The Society of Automotive Engineers (SAE) has developed test practices to measure the RRC of tires. The coefficient is mostly considered as independent of speed, but for precise calculations it is tabled at several speeds or an additional speed-dependent part is used. A lower coefficient means the tires will use less energy to travel a certain distance. Rolling resistance can be expressed by the rolling resistance coefficient (RRC or C rr), which is the value of the rolling resistance force divided by the wheel load. Such tires are now commonly installed as standard, either mandated by law or to meet eco labelling standards. Low rolling resistance tires are designed to reduce the energy loss as a tire rolls, decreasing the required rolling effort - and in the case of automotive applications, improving vehicle fuel efficiency as approximately 5–15% of the fuel consumed by a typical gas car may be used to overcome rolling resistance. ![]() ![]() Tires that improve vehicle fuel efficiency compared with conventional tires
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