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Brake Testing - by Clay Campbell and Ted Kobayashi |
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The Boster, Kobayashi organization has long enjoyed a working relationship with the Oakland Police Department (OPD) Traffic Division. We not only provide on-going professional expertise on an as-needed basis, but we have participated in vehicle brake testing with their personnel. One series of tests involved a comparison of the braking capabilities of vehicles with and without antilock brakes on dry, then wet, pavement. Participating in the testing from our firm were Tom Boster, Clay Campbell and Ted Kobayashi. Lieutenant Bernie Gerhard, Sergeant Doug Wayne and Officer Charles Teich were participants from the OPD. In
the area of testing, the roadway was level with a 1.2 degree
cross slope. The
temperature was approximately 70 degrees and the relative
humidity was approximately 80 percent.
The roadway surface was initially dry.
The tests were conducted between |
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Three
vehicles were tested, an OPD 1985 Ford LTD, a 1987 Mercedes Benz
190E equipped with antilock brakes, and an OPD 1985
Harley-Davidson FXRP motorcycle.
Each vehicle was inspected prior to the test.
The make, model, and size of tires were recorded, as well
as tire pressure and tread depth.
A paint marker gun was attached to the front bumper of
the test car to record when the signal to brake was given and
when the brakes were applied.
In order to record the vehicle deceleration rate, an
accelerometer was installed in each vehicle.
Vehicle speed was recorded by the observer, using a radar
gun, when he signaled the driver to brake.
For the motorcycle, the rider attempted to maintain a
uniform speed until given the signal to brake.
The
data collected from each test include the speed at braking
distance from signal to brake, distance to brake application
using a two shot bumper gun, distance to begin tire skid and
skid distance. Deceleration
rates from the accelerometer were recorded for comparison with
skid test data. The
Ford and Mercedes Benz were tested twice with the roadway dry
and twice with the roadway wet.
The motorcycle was tested only on dry pavement.
Two tests were conducted using rear brakes exclusively,
and two tests were conducted using both the front and rear
brakes. When
reviewing the results, be assured that Sergeant Wayne is an
expert motorcyclist!
Based
on recorded distance from signal to brake and brake application,
and the speed of the vehicle at signal to brake, the driver’s
perception and reaction time ranged from 0.29 seconds to 0.37
seconds. These
results make sense when it is considered that driver Officer
Teich is a high-speed driving instructor, and he was aware of
the location where the brake signal would be given.
The
accompanying chart shows the measures of Coefficient of Friction
(COF), based on total and skid distances, for the three vehicles
tested. It also
provides the corresponding accelerometer results, when
available.
The day’s testing provided valuable hands-on experience, as well as data on the braking capabilities of two vehicles, one with antilock brakes. In addition, the test method and results provided a valuable tool for understanding the use of COF values in speed from skid analyses. An ideal departure point for discussions concerning the concepts of perception/reaction time, spin down and skid analysis was also afforded. Click on a thumbnail below to see a full size image.
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