Evening star., 1924-08-17
TESTING AUTOMOBILE BRAKES
BY FREDERIC J. HASKIN

If automobile fans Of the COS could
have looked forward to a scene which
occurred on the grounds of the WASH
ington Monument recently they would
have been surprised. They would have
seen Government expert spending two
entire afternoons testing the brakes of
automobiles. We can imagine the drivers
Of 1898 speed wagons saying to one an
other. ITO think Of having to be care
full about stopping an automobile! Why
an automobile can always be counted on
to stop even when it ought to keep 60
ing"
This is by way of saying that brakes
may not have been a vital organ of
early motor cars, but as high-powered
engines have become more common, and
as traffic has become more and more
congested, brakes have increased in i'm
portance. Whether on city street or
on broad highway the motorist never
knows when he may need to stop his
car quickly within a short space.
There are no conclusive statistics
showing to what extent defective brakes
are responsible for accidents. Some
writer's have gone so far as to express
the opinion that the majority Of traffic
accidents could be traced to brake diff
culties This statement may or may not
be an exaggeration.
There are definite statistics, however.
on the condition Of brakes in cars that
are In constant use, and the figures
show that few cars have brakes in ex-
cellent or even good condition.
Last week the Bureau of Standards
onered to test the brakes of any car
that was brought to the Washington
Monument grounds on two afternoons
The announcement brought $50 auto
mobiles, including Gen. Pershing's car
and that of Traffic Court judge.
H. n. Allen, mechanical engineer of
the Bureau of Standards, was the
tester who officiated, and he had for
equipment only a decelerometer. This
instrument with the long name is
small and portable. 1t is placed un-
attached in an automobile. and then
the engine Is run at any desired speed
and the car brought to a stop by use
Of the brakes. Whatever the actual
speed of the car, needle On the
decelerometer indicates the number
of feet the car requires to stop at the
speed of 20 miles an hour.
How Cars Arc Rated.
The Bureau of Standards scheme
Of rating cars is used with the under
standing that it Is arbitrary and only
tentative. The service or foot brakes
Of any car that could not be stopped
in so feet were rated poor. A car
that stopped between 40 and so feet
was rated fair on it's brakes. A stop
between 80 and 40 feet was good, and
under 80 feet excellent.
Tested on a dry asphalt pavement,
18 per cent Of the cars were poor,
% per cent fair, A per cent good and
Is per cent excellent by the Govern
ment rating scheme. The general
average for service brakes on all $50
cars was 45.4 feet. The best stop
was II feet, and the poorest was 80
feet. The cars of Gen. Pershing and
the traffic Judge came of with the
rating Of good.
When pavements are wet, traffic
dangers Increase and the need for in
slant response from brakes Is greater.
What can be expected from the foot
brakes of the average car on a rainy
day Is shown by the test ratings.
None of the foot brakes tested by the
Government was good and none ex-
cellent on wet pavement. The average
stopping distance in the poor class
was 63 feet. Only one car got into
tho fair class It's stopping distance
WaS - feet.
The II cars having four-wheel
beakes made . better showing. The