The field of tyre dynamics is a relatively new, but highly complex field of engineering. The testing and modelling of various tyres in order to determine stress distributions of tyres on the road surface, under varying conditions, remains a relevant and important field of study. The information from these studies are essential to understanding vehicle dynamics as the small contact patches between the vehicle tyres and road surface is the only area of interaction between the entire vehicle and the road surface. The contact stress data is also essential in the calculation of road wear characteristics of tyres and vehicles. Different models exist to estimate the contact stress between the tyre and road surface, but most contain assumptions that limit their applicability to a small set of tyres under very specific load cases. This paper considers the development of mathematical models that are used to estimate the vertical uniform contact stress for three types of heavy vehicle tyres. The three tyres studied are 315/80 R22.5, 385/65 R22.5 and 425/65 R22.5 tyres. The models have been developed through the use of tyre testing data obtained from the Stress-In-Motion (SIM) system. It was found that 4th order polynomials provided the most accurate stress results over the selected operating range of 25 kN to 45 kN which is the typical load range for heavy vehicle tyres due to legal axle load limits. The polynomial formulas require only the tyre inflation pressure and vertical tyre load as inputs, in order to estimate the vertical uniform contact stress. The models developed correlate well with the test data and showing an average absolute error of less than 2 %.
Paper presented at the 35th Annual Southern African Transport Conference 4-7 July 2016 "Transport ? a catalyst for socio-economic
growth and development opportunities to improve quality of life", CSIR International Convention Centre, Pretoria, South Africa.