COEFFICIENTS OF FRICTION BETWEEN RUBBER TIRES AND CONCRETE ROAD SURFACES
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Abstract:
THE QUESTION IS RAISED AS TO WHETHER THE COEFFICIENT OF IMPENDING SKID, THE COEFFICIENT OF SLIDING FRICTION OR THE DIFFERENCE BETWEEN THE TWO IS THE CRITICAL FACTOR IN ROAD SKIDDING, AND SUGGESTIONS FOR STUDY OF THIS PROBLEM ARE MADE. CONCRETE PAVEMENTS WERE FOUND IN MOST OF MOYER'S TESTS TO HAVE COEFFICIENTS FOR STRAIGHT AND SIDE SKIDDING WITHIN RANGES THEORETICALLY REASONABLY SAFE FROM DANGER OF SKIDDING. METHODS FOR PRODUCING SURFACES WHICH MAY HAVE HIGHER COEFFICIENTS OF FRICTION ARE ALSO DISCUSSED. /AUTHOR/Keywords:
Skid (aerodynamics)
Coefficient of friction
Static friction
Frictional coefficient
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Summary A vehicle skids whenever the friction between tyre and road is insufficient to meet the demands of the driver in accelerating, braking, or cornering. In wet weather, when the water film on the road acts as a lubricant, the friction between tyre and road may be greatly reduced. The magnitude of the friction between a tyre and a wet road depends on the physical characteristics of both the road surface and the tyre. Recent work has shown that when well-lubricated rubber slides over a hard surface, as in the case of a tyre on a wet road, a large part of the frictional resistance may arise from energy losses in the rubber as it is deformed by projections in the hard surface and then recovers. These are the so-called hysteresis losses. Evidence suggests that if the associated practical problems can be solved very worthwhile improvements in skidding friction may be obtained by the use of tyres in which the rubber of the tread has much higher hysteresis losses than the normal tyre tread rubber.
Road surface
Hysteresis
Rolling resistance
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The coefficient of friction for a vehicle's tires sliding on a road surface is a critical parameter in calculating the speed of a vehicle involved in a motor vehicle collision. Theoretically, the amount of air pressure in the vehicle's tires and tread wear should not have a significant effect on the coefficient of friction between the tires of a skidding vehicle and the road surface. Skid tests were conducted to determine the effect of different tire pressures and tread wear on the coefficient of friction on an asphalt road surface. Each of the four tires on the vehicle were set to the same tire pressure for each skid test and were set from 45 to 5 pound per square inch (310.26 to 34.47 kilopascals). Various tire brands with varying age and tread wear were used for the tests. Average friction coefficient ranges for both wet and dry asphalt were measured. These values were compared to a hypothetical infinitely large data sample and no substantial difference was found regardless of the tire tread wear and tire pressure.
Skid (aerodynamics)
Coefficient of friction
Road surface
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A METHOD IS SUBMITTED FOR CALCULATING THE THEORETICAL STOPPING DISTANCES OF AUTOMOBILES BY AVERAGING THE COEFFICIENTS OF FRICTION ON THE BASIS OF THE SQUARE OF THE SPEED. THE RESULTS POINT OUT THE LOWER COEFFICIENTS GENERALLY FOUND AT THE HIGHER SPEEDS. SUCCESSIVE TESTS ON VERTICAL-FIBER WIRE-CUT LUG BRICK ROADS WITH ASPHALT FILLER HAVE SHOWN A CONTINUED DECREASE IN BOTH THE MAXIMUM ROLLING AND THE SLIDING COEFFICIENTS OF FRICTION DUE TO THE EXTRUSION OF THE ASPHALT. IN TESTS ON SNOW, NON-SKID TIRES SHOWED AN ADVANTAGE OF 7 TO 27 PERCENT OVER SMOOTH TIRES AT SPEEDS BETWEEN 20 AND 40 MILES PER HOUR. ROLLING COEFFICIENT FOR THE 5.00 INCH NON-SKID TIRE WAS 12 PER CENT BETTER THAN FOR THE 6.50 INCH TIRE WHEN STOPPING FROM 40 MILES PER HOUR BUT SHOWED NO DIFFERENCE WHEN SLIDING. FOR SMOOTH TIRES, THE 5.00 INCH TIRE HAD AN ADVANTAGE OF 8 AND 14 PERCENT OVER THE 6.50 TIRE FOR ROLLING AND SLIDING RESPECTIVELY. /AUTHOR/
Skid (aerodynamics)
Coefficient of friction
Frictional coefficient
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This article provides a list of sources for coefficient of friction values for use when a motorcycle slides during a collision sequence. Reports from 13 tests are summarized. Most of the values are for standard motorcycles, which have a variety of protrusions that tend to interact with the roadway surface to gouge or scrape when the motorcycle is sliding. Application of any particular coefficient of friction in a real-world collision should consider the manner in which the motorcycle traveled across the roadway surface and the degree of scraping or gouging that occurred during the slide. In general, the greater the degree of roadway gouging and scraping, the higher the coefficient of friction. It is suggested that a range of coefficients of friction be used for each set of calculations performed in order to increase the probability of calculating an accurate estimate of energy loss.
Coefficient of friction
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A reliable online prognosis of the grip between tire and road is a feature with a big potential for further improvements of the automotive safety. Existing grip potential prognosis systems for wet conditions are able only to describe the hydrodynamic decrease of friction at high speeds which depends on vehicle velocity, water film thickness and drainage properties both of the road surface and the tire. The present work deals with the friction at low speeds which depends on the road micro roughness. The experimental investigations are done in laboratory using a small solid rubber wheel and several asphalt samples. All parameters possibly influencing the friction process are varied. The influence of the test surface is found to be related to the micro texture and to be independent of any other parameters.
Road surface
Rough surface
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RESULTS are presented of measurements of road roughness and skid resistance for more than 50 different road surfaces in california. It is believed that the basic design of the bureau of public roads roughness trailer used in these tests is fundamentally sound and it provides the simplest and most accurate measure of road roughness. Skidding resistance measurements were made on dry and wet surfaces by three different methods: (1) towing a trailer with a truck at constant speed and recording the speed and braking effort with one trailer wheel locked, (2) locking all wheels of the passenger car and measuring the total stopping distance, and (3) locking all wheels of a passenger car and recording the speed and rate of deceleration by means of electronic and oscillograph equipment. The high type pavement surfaces on rural state highways in California were found to have the best riding qualities of all the various types of surfaces tested. The roughness of asphalt surfaces with seal coats was almost double the roughness measured on the high type pavements. The widest spread in roughness values was obtained in the measurements of the roughness of city streets. Friction values for rounded aggregate were about 25% lower than for angular aggregate in the wet skid resistance test. Slightly higher friction values were obtained on open-graded surfaces than on dense-graded surfaces although the sharpness or grittiness of the aggregate was a major factor influencing the test results. Friction values on open-grid steel bridge floors were very high in the dry test but were dangerously low in the wet test. Friction values for synthetic rubber tires with a good tread were about 5% higher than for natural rubber tires in the wet test and on the various paved surfaces. These tests indicated that the greatest skidding hazard is encountered when braking a car with smooth tread tires with all wheels locked or skidding on a wet glazed asphalt surface.
Skid (aerodynamics)
Trailer
Towing
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Abstract : It was found that low friction coefficients were responsible for some aircraft accidents on naval airfields. Basic studies indicated that the actual friction coefficients between tires and pavement surfaces did not follow the basic laws of friction. The total frictional force included, in addition to the basic frictional force, a mechanical force resulting from the interlocking of the rubber with the aggregate particles protruding above the pavement surfaces. Various field-testing devices, developed by others, were used and compared in an effort to locate low-friction pavements and to standardize the method of measurement. One device still in the development stage showed promise of measuring friction coefficient under simulated conditions of landing aircraft. Many factors affecting the friction coefficient between tires and pavement surfaces were found through laboratory and field investigations. These factors were related to vehicle and aircraft operation, to tire design, and to types of pavement surfaces. The effect of these factors on the friction coefficients were varied. The individual effects of each factor were not found since many of the factors worked in combination.
Coefficient of friction
Frictional coefficient
Interlocking
Dynamical friction
Static friction
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Anecdotal evidence indicates that the presence of contaminants in the tyre/road interface reduces the friction generated between the tyre and the road and that the sudden reduction in friction over the area affected can contribute to a driver loosing control of a vehicle. This report presents the results of an investigation of the effect of various types of road surface contamination on the measured friction. Tests were carried out on two surfaces at an ex-USAF base at Bentwaters Park, Suffolk - one asphalt, the other concrete. Peak and sliding coefficients of friction were measured at speeds up to 80km/h with a locked-wheel pavement friction tester (PFT) and two skid cars. The PFT used a completely smooth test tyre and the skid cars were fitted with normal road tyres in roadworthy condition. The contaminants with which these surfaces were tested were diesel oil, engine oil, clay and coarse sand; additional tests were carried out after a proprietary absorbent material had been applied to the diesel oil and engine oil. The main conclusion is that friction coefficients for cars with tyres in good condition are no worse than might be expected for many road surfaces when wet, but that tyre tread is critically important to this performance: friction coefficients of practically zero can be observed with smooth tyres, even with an underlying surface that is highly skid resistant. (A)
Skid (aerodynamics)
Road surface
Lubricity
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A detailed investigation has been made of the skidding resistance of smooth and patterned tyres with different treads of seven polymers. The tyres were tested over a very wide speed range (1 to 140 km/h) on eight test track surfaces characterised by different micro and macro textures. These tests formed part of a road and laboratory programme to investigate the complex visco-elasto hydrodynamic mechanism of tyre/wet road friction. In practice it was found that the effects of extremes of surface are greater than the extremes of tyre tread polymer and pattern combined. Though all factors can play a part in providing good tyre/road grip in wet conditions the relative importance of the tyre and road surface texture reverses over the practical motoring speed range. It appears that hysteresis alone does not account for the high skidding resistance measured on some surfaces at high speeds but that the sequence of events arising from hysteresis losses on rough surfaces creates tyre/road contact conditions corresponding to lower speeds so that adhesion becomes directly and hysteresis indirectly responsible for the increased skidding resistance. /Author/TRRL/
Road surface
Hysteresis
Texture (cosmology)
Rolling resistance
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DATA ARE PRESENTED FOR MANY DIFFERENT TYPES OF PAVEMENTS WHEN DRY, SET, AND SNOW- AND ICE-COVERED, WITH THE LATEST TYPES OF RUBBER TIRES INDICATING THE IMPORTANCE FOR PRECISE MEASUREMENTS OF COEFFICIENTS OF FRICTION FOR THE DESIGN OF MODERN STREETS AND HIGHWAYS AND FOR DEVELOPING PROGRAMS FOR THE PREVENTION OF SKIDDING ACCIDENTS. THE LARGE INCREASE IN VOLUME AND THE INCREASED SPEEDS OF PRESENT-DAY TRAFFIC IS CONTRIBUTING TO AN INCREASED AMOUNT OF AGGREGATE POLISHING, CONTRIBUTING TO A MARKED INCREASE IN THE SKIDDING HAZARD OF WET PAVEMENTS. THE TESTS REPORTED INDICATE THE LARGE DECREASE IN THE COEFFICIENTS OF FRICTION WITH AN INCREASE IN SPEED ON WET PAVEMENTS. A NATIONWIDE PROGRAM FOR THE PRECISE MEASUREMENT OF COEFFICIENTS OF FRICTION OF WET PAVEMENTS IS PROPOSED USING STANDARDIZED SKID TEST EQUIPMENT AND TESTING PROCEDURES. A SERIES OF CORRELATION SKID TESTS IS FURTHER PROPOSED. IT WAS FOUND THAT THE TESTING UNITS DESIGNED TO MEASURE THE ROAD FRICTION FORCES USING A DRAWBAR-TYPE MEASURING SYSTEM INTRODUCED AN ERROR FOR THE COEFFICIENTS OF FRICTION OF AS MUCH AS 20 PERCENT LOWER THAN THE TRUE COEFFICIENTS OF FRICTION. A BRAKE REACTION TORQUE METER SKID TEST UNIT DEVELOPED IN THE TEST PROGRAM IS DESCRIBED WHICH PROVIDED A MEASUREMENT OF THE COEFFICIENTS OF FRICTION WITH AN ACCURACY OF PLUS OR MINUS 1 PERCENT. THE RESULTS OF THE SKID RESTS ON THE VARIOUS TYPES OF PAVEMENTS COVERED A WIDE RANGE OF VALUES FROM THE LOW FRICTION VALUES OF 0.17 TO 0.30 AT 40 MPH FOR THE SLIPPERY-WHEN-WET PAVEMENTS WITH A DENSE- GRADED, POLISHED AGGREGATE-TYPE FINISH, TO VALUES IN THE HIGH FRICTION RANGE OF 0.40 TO 0.60 AT 40 MPH FOR SURFACES WITH A COARSE-TEXTURED, OPEN-GRADED TYPE OF FINISH. RESULTS OF TESTS WITH 4 DIFFERENT TIRES ALSO VARIED CONSIDERABLY IN TESTS ON THE SAME SURFACE AND AT THE SAME SPEED. THE HIGHEST FRICTION VALUES WERE MEASURED WITH THE BUTYL RUBBER TIRE FOR WHICH THE FRICTION VALUES WERE FOUND TO BE 15 PERCENT TO 40 PERCENT HIGHER THAN FOR THE SMOOTH TREAD TIRE WHICH YIELDED THE LOWEST FRICTION VALUES. THE HIGH FRICTION VALUES MEASURED WITH THE BUTYL RUBBER TIRES WERE SO PROMISING THAT IN FUTURE PROGRAMS FOR PREVENTING SKIDDING ACCIDENTS, IMPROVEMENTS IN TIRE TYPES MAY BE MORE ECONOMICAL AND FULLY AS EFFECTIVE AS THE PROPOSED IMPROVEMENTS IN SKID RESISTANCE OF PAVEMENTS. /AUTHOR/
Skid (aerodynamics)
Coefficient of friction
Trailer
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