Measuring Grip and the Contact Patch

Abstract

A vehicle or air-craft tire interacts with a surfacing through its contact patch. Wet grip is one of the most important properties of a highway or airfield surfacing. This paper looks at the contact patch for the GripTester device, widely used around the world to assess both highway and air-field skid resistance. Contact patch properties were measured using a XSENSOR pressure mapping system. The relationships between inflation pressure and properties such as contact area, length and width were assessed for a new and worn GripTester tire. Pressure mapping was found to provide high quality data with the found relationships agreeing with previous research. Contact patch data was related to in-situ measurement of wet grip measured using GripTester fitted with both tires at a range of tire inflation pressures and for a range of asphalt surfacing types. These found robust relationships between inflation pressure, measured wet grip, contact patch area and tire wear. Most relationships were as expected, however it was found that increasing contact area related to a decrease in measured wet grip for the new tire. The distribution of contact pressure within the contact patch is suggested as one of a number of areas that warrant further consideration.