Experimental Estimation of On-Vehicle Wheel-End Force and Application to Tire Flat-Spotting Effect

Nibble is torsional vibration at the steering wheel of a vehicle. Typically it occurs at a resonant frequency of the steering and suspension system excited by the 1st harmonic tire/wheel force. A nibble target is established to be consistent with customer satisfaction target and then cascaded down to the targets for vehicle nibble sensitivity and tire/wheel inputs. Hence accuracy of the sensitivity and the tire/wheel force is important for a Computer Aided Engineering (CAE) nibble simulation. On-vehicle wheel-end forces are fore/aft and vertical tire/wheel forces acting on a vehicle spindle in an operating condition. This paper presents a methodology to estimate the wheel-end forces. The methodology was applied to investigate the effect of the tire flat-spot on the wheel-end forces. Tires were flat-spotted for one week and two months to simulate customer usage profiles. They were tested to measure the growth of the wheel-end forces. Finally, tires of the vehicles in a dealer lot were also tested with known “time-on-lot”. The new measurement that reflected a statistical distribution of the flat-spotted wheel-end forces improved the CAE load case for the nibble simulation and correlated “time-on-lot” to the nibble warranty.