Measurement of Tire Vertical Damping, Carcass Deflection and Longitudinal Relaxation Length

Three methods to experimentally determine specific tire characteristics are discussed. The vertical dynamic behavior of a rolling tire up to 10 Hz is analyzed using experiments with a prescribed, sinusoidal axle displacement. The transfer function between axle displacement and vertical axle force allows to identify stiffness, damping and effective mass. The identified vertical tire damping is a factor 2 to 3 higher than the 50 Ns/m typically used for passenger car tires. A rim fixed camera has been used to measure tire carcass deflections by tracking markers on the innerliner of the tire. Low speed experiments show that the lateral tire deflection correlates very well with the lateral tire force. The proposed method can be used to validate physical tire models and shows potential as a force sensor. The flat plank tire tester has been equipped with a motor that allows to prescribe the rotation of the wheel. This allows to perform a direct measurement of the longitudinal relaxation behavior by applying a longitudinal slip step. The experimentally obtained results are in line with theory and clearly show a decreasing relaxation length with increasing levels of longitudinal slip.