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Efforts to develope a harmonized brake standard have led to the developement and evaluation of procedures for measuring the brake balance and braking efficiency of passenger cars. The European braking regulations include a procedure for direct measurment of the braking efficiency of a vehicle equiped with an antilock system (ECE Regulation No. 13. Annex 13/EEC Directive 71/320 Annex X). The procedure is a two step process including the measurement of the peak coefficient of friction (mu) for the vehicle tire on the test surface, and then finding the maximum deceleration of the vehicle on the test surface for calculation of the braking efficiency. Tests were conducted to evaluate the feasibility of using this procedure for vehicles not equiped with ABS. Comparisons were made between the peak coefficient of friction as measured by the Annex 13 procedure and as measured by a traction trailer with the vehicle tires installed.

In this study, experimental methods were used to compare the consequences of employing snubbing versus dragging strategies to control the speeds of trucks on downgrades. Vehicle tests were performed on a long steep grade. A mobile dynamometer was used to study cooling rates and hot spotting. The basic findings of the study are: (1) the average temperature per pound (kilogram) of brake drum is practically equivalent whether light dragging or snubbing is used; (2) the hottest brakes will be cooler if snubbing is used; and(3) on short downhill descents, the dragging strategy will cause hot spots to develop to a greater extent. For many years there has been controversy between those that recommend dragging brakes versus those that recommend snubbing (pulsing) to control vehicle speed during downhill descents. Recently, interest in commercial driver licensing (CDL) has stimulated discussions of the merits of these two braking strategies.

Enhancements have been developed for low speed roller brake testers that make them more useful devices for testing and diagnosing braking systems. The enhancements are primarily designed for the evaluation of air brake systems but have application to hydraulic brake systems as well.

A number of methods and types of equipment have been developed to measure a heavy vehicle's braking forces both for use as an inspection tool and for diagnosis of brake system problems. The systems and procedures evaluated included a vehicle deceleration test, a road transducer plate, roller dynamometers, a flat plate tester, a breakaway torque tester, and an infrared brake temperature measurement system. Evaluations of these devices have been conducted to ensure that the results produced are meaningful. In general, the devices compare very well and, in most cases, were found to be useful in determining the status of a brake system.

A vehicle test procedure for determining the adhesion utilization properties of braking systems has been developed. The procedure requires minima instrumentation and equipment. It was applied to 19 passenger cars over a range of conditions and the effects of factors such as load, center of gravity height, speed, parasitic drag, engine braking, drive configuration (front or rear), brake conditioning, and tire properties on adhesion utilization were determined. The vehicles were also subjected to a series of stopping tests on six different surfaces to evaluate the degree of correlation between predictions from the adhesion utilization curves and actual performance. Frictional properties of the tires from 11 of the vehicles were measured on the surfaces to aid in this correlation study.

This paper serves as the seventh report in a series of reports on NHTSA's Heavy Vehicle Brake Research Program and deals with the subject of tractor and trailer brake system compatibility. It provides a detailed definition of compatibility, discusses the factors that influence it and presents data and analyses which indicate the degree of compatibility in the heavy duty combination vehicle fleet at large. The paper suggests ways in which compatibility can be improved so that combination vehicle brake systems will be more durable and provide an enhanced level of safety.

Currently there are no adequate standards or regulations that address the performance of aftermarket replacement brake linings to insure that the use of these materials does not degrade vehicle braking performance from the original equipment (OE) design intent level. This paper discusses the results of an evaluation of a large sampling of aftermarket linings available for the rear brake of a specific model passenger car and shows that many of these linings have significantly different performance than the OE material. The paper also shows how this deviation can adversely affect vehicle braking efficiency or the ability of the brake system to utilize available tire/roadway friction without locking wheels and losing control.