Next to power, applied
through the correct form of
gearing, and its final suita-
ble drive to the road wheels,
nothing is of more importance than the ability to stop the vehicle at
will. One medium through which this is done, and which ordinarily
suffices, is the shutting off of the source of power — ^in this case, the
closing of the throttle which feeds the gas to the cylinders. This will
not always suffice, however, for the ordinary car possesses the ability
to run at a speed of 40 miles per hour or upward, and weighs from 2000
pounds (one ton) upward to 4000 pounds (two tons). This combi-
nation makes for a large force of inertia, which will result in the car
running for many yards, even hundreds of yards, after the power is
shut off. It is for this reason that we must have a mechanical
means of absorbing this inertia, or of snubbing the forward move-
ment of the car. This is the function of the brakes, as fitted to
the modern car.
250



GASOLINE AUTOMOBILES 583

Engine as a Brake. Although disregarded in any summary of
brakes, the engine is the best brake possible, granting that the driver
knows how to get the best results without doing any damage. The
ordinary engine has a compression of from 60 pounds to 70 pounds per
square inch, which is practically the pressure available when it is used
as a brake. As this pressure offers a great deal of resistance the brak-
ing effect is self-evident.
