EVALUATION OF WINTER-DRIVING TRACTION AIDS

A set of test procedures has been selected to measure the braking, driving traction, and controllability of (1) vehicles fitted with tires and tire-associated traction aids intended to increase available friction on ice and snow surfaces and (2) vehicles fitted with drive-train aids intended to make better use of available friction. The performance of traction-aids intended to increase available friction, such as tire chains, snow tires, studded tires, and improved rubber compounds, may be determined from a combination of the following test data: 1. Locked-wheel braking friction or locked-wheel stopping distance at a speed of 20 mph (32.4 km/hr). 2. Spinning driving traction at a vehicle speed of 5 mph (8.1 km/hr) with the traction force measured at a slip ratio greater than 1. 3. Spinning driving traction with the test vehicle stationary and tire slip speed greater than 10 mph (16.2 km/hr); and 4. Limiting (minimum) lateral tire force measured with a single-wheel tester. The standardized test procedures for obtaining the test data are described in the report. The performance of traction-aids intended to make better use of available friction, such as the limited slip differential, nonlocking brakes, and the four-wheel drive, may often be calculated directly from the relevant vehicle characteristics and an assumed tire/friction factor. A simulation program was written and used to study the controllability performance of vehicles fitted with these aids. (Author)