Rolling Resistance Revisited

Rolling resistance defined as energy loss per unit distance is well accepted by the tire science community. It is commonly believed that the dominant part of energy loss into heat is caused by the viscoelasticity of rubber compounds for a free-rolling tire. To calculate the rolling loss (hysteretic loss) into heat, a method based on tire forces and moments has been developed to ease required measurements in a lab or field. This paper points out that, by this method, the obtained energy loss is not entirely converted into heat because a portion of the consumed power is used to compensate mechanical work. Moreover, that part of power cannot be separated out by tire forces and moments–based experimental methods. The researchers and engineers have mistakenly ignored this point for a long time. The finding was demonstrated by a comparative analysis of a rigid, pure elastic, and viscoelastic rolling body. This research mathematically proved that rolling loss into heat is not resolvable in terms of tire forces and moments with their associated velocities. The finite element model of a free-rolling tire was further exercised to justify the concept. These findings prompt revisiting rolling resistance in a new way from the energy perspective. Moreover, an extended definition of rolling resistance is proposed and backward compatible with its traditional definition as a resistive force.