The CPSC road test of bicycle braking performance - kinetic and error analyses

Abstract

The Consumer Product Safety Conmission has promulgated a safety standard for bicycle braking systems based on the stopping distances achieved in road tests under specified conditions. This report presents an error analysis of the test method, for the Commission's use in justifying or modifying the test criteria. The error analysis is based on experimental data, for the most part, and on theoretical principles where sufficient data are lacking. The theory, a kinetic analysis of the bicycle braking process, is included in the report together with proposed definitions of terms intended to quantify important aspects of bicycle braking performance.The error analysis produced estimates of rather large lab-to-lab and test-to-test variabilities to be expected from the test method. These, in turn, were found to be principally dominated by errors resulting from an incorrect overweight-rider allowance specified by the Commission, and by variations in rider reaction times, respectively. Suggestions are made for more accurate methods of accommodating variations in rider mass, for reducing the effects of the test-to-test variability, and for reducing the danger of pitchover in the performance of the road test.

Analyses of riding tests for evaluating the wet braking performances of bicycles

“…For the sake of specificity, this study is principally concern ed with a typical bicycle having handlever-operated caliper brakes on both wheels, and marginal braking capability. The essential characteristics of the typical bicycle [2] are reproduced in Table 1 3 Numerals in square brackets refer to similarly numbered references listed in Section 7 of this report.…”

“…Some of these test conditions are based on analyses reported in NBSIR 75-786 [2] , which were carried out by the National Bureau of Standards (NBS ) on an earlier version of the safety regulations [3].…”

“…-1 - Coordinates of the center of gravity of the bicycle with an average 68.1-kg (150-lb) rider: A bicycle exhibits marginal braking capability [2] when it is brought to a stop over a distance of exactly 4.57 m (15.0 ft) under the standard test conditions.…”

“…The standard test conditions [2] include: an average 68.1-kg (150-lb) test rider; an initial speed of 24 km/h (15 mph) ; the application of 178-N (40-lbf) forces to the handbrake levers; and a dry, clean, level, paved test course which offers a uniform coefficient of friction of 0.75 at the tire/pavement interface of a locked bicycle wheel.…”

“…An average test rider is one of average physical characteristics who provides an average reaction time of 0.15 seconds [2], Reaction time is the interval between the instant at which the rider first begins actuating the handbrake levers and the instant at which the prescribed force levels are reached [2] .…”