Within the accident reconstruction community, skidmarks and yaw marks are utilized in the speed analysis portion of an investigation to determine vehicle speeds during an accident sequence. Many times in an accident involving tire marks, a skid test is performed at the scene with a law enforcement vehicle utilizing performance type tires to determine the coefficient of friction at the tire-roadway interface. The primary purpose of this paper is to quantitatively assess differences which may exist between performance type tires often utilized on law enforcement vehicles and typical production type passenger car tires relative to tire-roadway friction.
Historically, the main source for friction coefficients at the tire-roadway interface within the accident reconstruction community has been from research conducted by Northwestern University. This published research was conducted in excess of twenty years ago, and, furthermore, is believed to have been largely conducted in the northern midwestern states.
A secondary purpose of this paper is to compare current tire-roadway friction coefficients of various tires on both front and rear wheel drive vehicles with the aforementioned data.
Another objective of this research is to evaluate any significant differences which may exist between the road surfaces indigenous to the south central United States and the published data of Northern University.
The Northwestern University research was largely conducted at a time when bias ply tires were more prevalent than radials. A further objective of the paper is to compare any differences which may exist at the tire-roadway interface between bias ply and radial tires.
Tire-roadway friction testing using four vehicles and six sets of tires was performed on both concrete and asphalt surfaces. Actual testing consisted of locked wheel braking at two different speeds for each tire/vehicle/surface combination. The four test vehicles included. two front wheel drive and two rear wheel drive passenger cars. The six sets of tires consisted of one set of bias ply, two sets of standard production vehicle radials, and three sets of performance type radials. The testing was conducted from early morning to late afternoon over a period of two days in order that a full range of ambient daytime temperatures be encountered.