J2452) are usually performed on new tires. When measured by using these standard test practices, most new passenger tires have reported RRCs ranging from 0.007 to 0.014." In the case of bicycle tires, values of 0.0025 to 0.005 are achieved. These coefficients are measured on rollers, with power meters on road surfaces, or with coast-down tests. In the latter two cases, the effect of air resistance must be subtracted or the tests performed at very low speeds. The coefficient of rolling resistance b, which has the dimension of length, is approximately (due to the small-angle approximation of ) equal to the value of the rolling resistance force times the radius of the wheel divided by the wheel load. ISO 18164:2005 is used to test rolling resistance in Europe. The results of these tests can be hard for the general public to obtain as manufacturers prefer to publicize "comfort" and "performance". Physical formulae The coefficient of rolling resistance for a slow rigid wheel on a perfectly elastic surface, not adjusted for velocity, can be calculated by where is the sinkage depth is the diameter of the rigid wheel The empirical formula for for cast iron mine car wheels on steel rails is: where is the wheel diameter in inches is the load on the wheel in pounds-force As an alternative to using one can use , which is a different rolling resistance coefficient or coefficient of rolling friction with dimension of length. It is defined by the following formula: where is the rolling resistance force (shown in figure 1), is the wheel radius, is the rolling resistance coefficient or coefficient of rolling friction with dimension of length, and is the normal force (equal to W, not R, as shown in figure 1). The above equation, where resistance is inversely proportional to radius seems to be based on the discredited "Coulomb's law" (Neither Coulomb's inverse square law nor Coulomb's law of friction). See dependence on diameter. Equating this equation with the force per the rolling resistance coefficient, and solving for , gives = . Therefore, if a source gives rolling resistance coefficient () as a dimensionless coefficient, it can be converted to , having units of length, by multiplying by wheel radius . Rolling resistance coefficient examples Table of rolling resistance coefficient examples: For example, in earth gravity, a car of 1000 kg on asphalt will need a force of around 100