Optimization of road pavement design, especially towards the surface of the pavement,
requires a more rational approach to modeling of truck tire-road contact stresses. Various road surfacing
failures are given in this paper as examples, and it is shown that the traditional civil engineering tire model
represented by a single uniformly distributed vertical contact stress of circular shape is inadequate to
explain this type of surface failure. This paper therefore discusses the direct measurement of threedimensional
(3D) tire pavement contact stresses using a flatbed sensor system referred to as the “Stress-In-
Motion” (SIM) system. The SIM system (or device) consists of multiple conically shaped steel pins, as well
as an array of instrumented sensors based on strain gauge technology. The test surface is textured with skid
resistance approaching that of a dry asphalt layer. Full-scale truck tires have been tested since the mid-
1990s and experience shows that 3D tire contact stresses are non-uniform and the footprint is often not of
circular shape. It was found that especially the vertical shape of contact stress distribution changes, mainly
as a function of tire loading. In overloaded/underinflated cases, vertical contact stresses maximize towards
the edges of the tire contact patch. Higher inflation pressures at lower loads, on the other hand, result in
maximum vertical stresses towards the center portion of the tire contact patch. These differences in shape
and magnitude need to be incorporated into modern road pavement design. Four different tire models were
used to represent a single tire type in order to demonstrate its effect on road pavement response of a typical
South African pavement structure. Only applied vertical stress was used for the analyses. It was found that
road surface layer life can reduce by as much as 94 percent as a result of simply using a different tire model
on the same pavement structure.