TRACTION CHARACTERISTICS OF TRUCKS AND TRUCK COMBINATIONS-- 1969 WINTER TRACTION TESTS

CONTROLLED ENGINEERING TESTS WERE CONDUCTED OF TRACTOR-SEMITRAILER COMBINATIONS MADE OF THREE 27-FOOT TRAILERS PULLED BY 6X4,4X4 AND 4X2 TRUCK-TRACTORS ON THE WEST GRADE OF THE MT. HOOD HIGHWAY. TEN TRIPLES COMBINATIONS WERE SUCCESSFULLY TESTED. THE HIGHWAY SECTION CLIMBS 3,000 FEET IN EIGHT MILES, THE UPPER PORTION HAVING A THIRD LANE FOR PASSING. THE GRADES RANGE UP TO 6.0%, AND THE PAVEMENT IS COVERED WITH A THICK LAYER OF LIGHTLY SANDED PACKED SNOW IN THE UPHILL LANES. NO PROBLEMS WITH MANEUVERING, BRAKING, PASSING OR STABILITY WERE ENCOUNTERED DURING THE TWO DAYS OF TESTING. THE HIGHWAY WAS SHARED WITH NOMINAL TRAFFIC DURING THE TEST. THE MOST CRITICAL TRACTION SITUATION WAS FOUND TO BE IN AN INTENTIONAL STOP-START TEST ON A LIGHTLY SANDED SNOW-COATED ROAD UPHILL 6.0% GRADE. STOP-START TESTS SHOWED THAT ALL VEHICLES WERE ABLE TO RESTART WITH CHAINS ON DRIVEN WHEELS. THIS WOULD BE THE USUAL OPERATING CONDITION. CHAINED UP DUPLEX TIRES PROVIDED LESS TRACTION THAN THE CHAINED UP STANDARD DUAL TIRES. THE COEFFICIENT OF TRACTION ON LIGHTLY SANDED PACKED SNOW WAS IMPROVED FROM 0.33 WITH ORDINARY CROSS-LINK CHAINS TO 0.35 WHEN CHAINS HAVING REINFORCED CROSS-LINKS WERE USED. ON SEVERAL RUNS, A TRUCK-TRACTOR WHICH HAD MARGINAL TRACTION ABILITY FOR THE GROSS COMBINATION IT WAS PULLING, COULD NEGOTIATE A PACKED SNOW SURFACE ON A 6.0% GRADE, IF IT KEPT ROLLING BUT COULD NOT RESTART AFTER BEING INTENTIONALLY STOPPED. THIS WAS DUE MAINLY TO THE ADDED DEMAND FOR TRACTION TO OVERCOME STATIC INERTIA AND ACCOMPLISH ACCELERATION. TEST RESULTS SHOWED THAT A TRACTION-LIMITED GRADE THAT IS FROM 0.50 TO 2.75% STEEPER THAN ON WHICH IT CAN START. SURPLUS HORSEPOWER DID NOT ENABLE THE TRUCK TO GO UP A STEEPER GRADE THAN THAT LIMITED BY TRACTION. AN EQUATION WAS DEVELOPED FOR TRACTION-LIMITED GRADES FOR A COMBINATION POWERED BY A 4X4 TRACTOR. AN EQUATION WAS VERIFIED FOR TRACTION-LIMITED GRADES FOR A COMBINATION POWERED BY A 4X2 OR 6X4 TRACTOR.

• Supplemental Notes:
  • Supplement NO 1, 43 PP, 14 FIG, 2 TAB, 1 APP
• Corporate Authors:

  Western Highway Institute

  San Francisco, CA  United States 
• Publication Date: 1970

Subject/Index Terms

• TRT Terms: Chains; Engineering; Equations; Horsepower; Mountains; Snow; Testing; Traction; Tractor trailer combinations; Trailers; Truck tractors
• Subject Areas: Highways; Motor Carriers; Safety and Human Factors;

Filing Info

• Accession Number: 00223345
• Record Type: Publication
• Files: TRIS
• Created Date: Oct 19 1970 12:00AM