Tire Footprint Analysis Based on Image Processing Techniques

The tire–terrain interaction is an essential criterion for assessing tire performance. Understanding the complex characteristics of the dynamic interactions of tires and terrain required a detailed and deep study on the characteristics of the contact patch area of the tire. Most of the studies conducted to determine the properties of the contact patch considered the tire-road interaction in a static condition and there are a limited number of research studies that focused on the dynamic behavior of the tire at the contact area especially when the real-time measurement of the dynamic contact area of the rolling tire with high slip ratio is the matter of interest. In order to completely understand the tire dynamics at the contact patch, a novel optical method based on light refraction and reflection is proposed for the measurement of contact area between the tread of the tire and a rigid transparent surface. To this end, constructing an indoor test rig is required. In this research, a three-dimensional drawing software Autodesk Inventor has been used to analyze a customized testing facility. An indoor test rig has been designed and manufactured to visualize the contact area of a rolling tire. A supporting mechanical system incorporated into this test rig allows providing the tire with variable camber angles and slip ratios. For the rolling tire, a digital camera GoPro has been used under a glass panel to record the tread pattern in detail when the tire passes over it during the test, to represent the footprint for a high slip ratio. From the image obtained with this system, the length, width, ratio, and shape of the patch can be determined, which are related to the effect on tire traction performance. This study specifically proposes a digital image correlation technology that can be used to capture the contact patch of a passenger car tire 205/55R16 and to obtain the geometry features of the contact area. Based on the appropriate image processing techniques in the MATLAB, a precise reconstruction of tire footprint was realized. The results for the footprint properties of the tire with an applied normal load of 4 kN and tire inflation pressures of 21 Psi for free rolling, static state, and the slip ratio of 0%, 2%, 4%, 6%, 8%, 10%, 12%, 15%, 20%, 25%, 30%, and 35% are presented. Presented results in the paper will show that the system is robust enough to obtain a real-time dynamic measurement. The novel method based on digital image processing revealed by the author can be validated as a precision measurement system of footprint characteristics.