TRACTION CHARACTERISTICS OF TRUCKS AND TRUCK COMBINATIONS

FULL-SCALE TRACTION TESTS WERE CONDUCTED ON HEAVY-DUTY TRUCKS ON A SUITABLE SKID PAD. THE FOLLOWING FOUR BASIC TESTS WERE INVOLVED IN THE PROGRAM: (1) TRUCK PULL-DOWN TRACTION TESTS, (2) PASSENGER PULL-DOWN TRACTION TESTS, (3) TRUCK ROLLING RESISTANCE TESTS, AND (4) PASSENGER CAR SKID TESTS. A GENERAL THEORY HAS BEEN ADVANCED WHICH COVERS THE TRACTION PROPERTIES OF ARTICULATED HEAVY-DUTY TRUCKS. THE THEORY PURPORTS TO ENABLE COMPUTATION OF THE STEEPEST GRADE ANY TRUCK CAN NEGOTIATE WITHOUT ITS DRIVEN WHEELS SLIPPING, PROVIDING THE WEIGHT DISTRIBUTION AND DIMENSIONS OF THE TRUCK OR TRUCK COMBINATION ARE KNOWN ALONG WITH THE COEFFICIENT OF TRACTION BETWEEN ITS DRIVEN WHEELS AND THE ROAD SURFACE. THE TRUCK PULL-DOWN SUBSTANTIALLY VERIFIED THE ACCURACY OF THE THEORY. EQUATIONS ARE PRESENTED FOR DETERMINING THE MAXIMUM GRADE WHICH CAN BE NEGOTIATED BY VARIOUS TYPICAL TRUCKS AND TRUCK COMBINATIONS. THE PASSENGER CAR PULL-DOWN TRACTION TESTS WERE MADE TO COMPARE THE TRACTION PROPERTIES OF PASSENGER CARS WITH HEAVY-DUTY TRUCKS AND TO HELP CORRELATE EXISTING DATA ON THE TRACTION PROPERTIES OF A TYPICAL PASSENGER CAR. DECREASING DESIGN TIRE INFLATION PRESSURES ON DRIVEN WHEELS WAS FOUND TO INCREASE DRIVE TRACTION ABILITY. THE ROLLING RESISTANCE TESTS WERE CONDUCTED TO DETERMINE THE ROLLING RESISTANCE FACTOR FOR VARIOUS TRUCK AND TRUCK COMBINATION TYPES SO THAT SUCH FACTORS COULD BE USED IN ANALYZING THE RESULTS OF THE TRUCK PULL-DOWN TRACTION TESTS. THE DIRECTLY MEASUREABLE QUANTITY IN A PULL-DOWN TRACTION TEST IS THE TOW CHAIN TENSION AT THE INSTANT WHEN DRY WHEEL SLIPPAGE BEGINS. IN ORDER TO OBTAIN THE VALUE OF THIS FORCE, TOW CHAIN TENSION MUST BE CORRECTED FOR THE ROLLING RESISTANCE OF THE TRUCK OR TRUCK COMBINATION BEING USED. PASSENGER CAR SKID TESTS WERE CONDUCTED TO ALLOW CORRELATION OF THE RESULTS WITH THE TRACTION TESTS AND WITH PREVIOUS SKID AND TRACTION TESTS. THE COEFFICIENT OF FRICTION BETWEEN TIRES AND PAVEMENT DEPENDS ON THE FRICTION VALUES OF BOTH. THE VALUE OF CHAINS ON SNOW, SAND, EARTH, ICE AND OTHER SIMILAR SURFACES IS DIRECTLY RELATED TO THE SHEAR STRENGTH OF SUCH SURFACE MATERIAL. THE GREATER RESISTANCE SUCH SURFACES HAVE TO SHEAR, THE GREATER THE BENEFIT DERIVED FROM CHAINS. CONSIDERABLE INFORMATION WAS OBTAINED RELATIVE TO MAXIMUM GRADES WHICH WAS COMPARED AGAINST THE DRIVE TRACTION ABILITY COMPUTED FOR THE VARIOUS TRUCKS AND TRUCK COMBINATIONS ON PAVEMENTS OF VARYING DEGREES OF SLIPPERINESS. A SHORT WHEEL BASE TRACTOR WAS FOUND TO OBTAIN MORE TRACTIVE BENEFIT FROM DYNAMIC FRONT TWO WHEEL TRANSFER THAN DOES A TRACTOR WITH A LONGER WHEEL BASE. DRIVE TRACTION ABILITY, THE GRIP OF THE POWERED WHEELS ON A SURFACE, IS INDEPENDENT OF GROSS COMBINATION WEIGHT. ONLY THE DYNAMIC WEIGHT UPON THE POWERED AXLES AND THE ROAD SURFACE ARE FACTORS.

• Supplemental Notes:
  • Rept No 1, 138 PP, 56 FIGS, 5 TAB, 3 APP
• Corporate Authors:

  Western Highway Institute

  San Francisco, CA  United States 
• Publication Date: 1969-1

Subject/Index Terms

• TRT Terms: Automobiles; Coefficient of friction; Inflation; Physical distribution; Rolling; Skidding; Surface course (Pavements); Testing; Theory; Tires; Traction; Tractor trailer combinations; Truck tractors; Trucks; Vehicle dynamics; Weight
• Old TRIS Terms: Resistance
• Subject Areas: Freight Transportation; Highways; Motor Carriers; Pavements; Vehicles and Equipment;

Filing Info

• Accession Number: 00207151
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 26 1970 12:00AM