Concept of Deformation Index to Calculate Energy Loss and Rolling Resistance of Tires

From a material standpoint, tire rolling resistance improvement is primarily achieved by modifing the tread compound.   Contribution from the remaining tire components, while individually small, collectively contribute more than fifty percent to the total energy loss in a passenger tire.   Historically, the compound tangent delta has been used as a measure of energy loss.   While this approach is acceptable for tread compounds, the losses associated with the remaining tire components depend on the type of deformations (stress, strain, or energy controlled) as well as their tangent delta values.   The "deformation index" is a simple way to determine the type of deformation and resulting energy losses.   The process of determining the deformation indices by FEA analysis is discussed.   Then, the relevant dynamic mechanical properties for energy loss are defined using the index for each tire component.   Finally, the loss contributions from all tire components are formulated into a spreadsheet so that changes in rolling reisitance can be estimated when compound properties are changed.   The method is interactive so that a compounder can ask “what if?” type questions in the process of total compound optimization for improved rolling resistance.