Locked wheel skid performance of various tires on clean, dry road surfaces

THE SKID PERFORMANCE OF SEVERAL MAKES OF TIRES ON CLEAN, DRY, LEVEL ROAD SURFACES WAS INVESTIGATED. FACTORS CONSIDERED INCLUDED SKIDDING VELOCITY, TIRE MAKE, WHEEL LOADING, AND TYPE OF ROAD SURFACE. DATA WERE OBTAINED FROM TRAILER DRAG TESTS AND PANIC STOPS OF PASSENGER VEHICLES. TESTS WERE PERFORMED USING TIRES OF FOUR DIFFERENT MAKES, THREE DIFFERENT ROAD SURFACES, AND SEVERAL DIFFERENT WHEEL LOADINGS. FOR THE DRAG TESTS, SKIDDING SPEEDS WERE FROM 10 MPH TO 50 MPH. PANIC STOPS WITH PASSENGER VEHICLES WERE MADE FROM SPEEDS OF 30, 40, 50, AND 70 MPH. IT WAS FOUND THAT AMONG DIFFERENT MAKES OF TIRES OF COMPARABLE QUALITY THERE EXISTED DIFFERENCES IN STOPPING ABILITY. DIFFERENCES IN THE LENGTH OF SKID AND BRAKING DISTANCE FOR A GIVEN INITIAL SPEED AND ROAD SURFACE TYPE WERE FOUND TO BE ABOUT TEN PERCENT FOR THE FOUR MAKES OF TIRES TESTED. SIMILAR DIFFERENCES WERE FOUND ON OTHER ROAD SURFACES. ONE OF THE MOST SIGNIFICANT FINDINGS WAS THAT THE COEFFICIENT OF FRICTION DEVELOPED BETWEEN A GIVEN TIRE AND ROAD WAS FOUND TO BE GREATER AT THE HIGHER SPEEDS. THIS TREND HAS NOT BEEN REPORTED BY OTHER INVESTIGATORS TO THE AUTHOR'S KNOWLEDGE. THE IMPLICATION OF THIS FINDING IS THAT EXISTING METHODS OF ESTIMATING PRIOR SPEED FROM LENGTH OF SKID MARKS LAID DOWN IN AN ACCIDENT INVARIABLY GIVES A CONSERVATIVE ESTIMATE OF SPEED. FOR A CAREFULLY EXECUTED EXPERIMENT, SPEED ESTIMATES WILL BE ACCURATE TO WITHIN FIVE PERCENT. /AUTHOR/