Short Stops

[Music] foreign [Music] more than any other America is truly a nation on wheels for example more than seven thousand cars have been counted in a single hour at the Leif Erickson bridge in downtown Chicago in New York City an almost endless stream of traffic more than eighty thousand cars a day flows past this busy corner this intersection in Detroit is traveled by enough cars each day to make a bumper-to-bumper parade 255 miles long in single file there are more than 27 million Motor Cars in the United States today more than half the total number of automobiles in the world if all the cars in the United States were driven three abreast along this street at 30 miles an hour night and day without a single stop the parade would go on for three months and then start all over again because the line would stretch more than completely around the Earth night and day in a hundred thousand cities and towns and Villages millions of cars are starting stopping moving in obedience to The Wills of millions of drivers in your own motor car when you step on the accelerator when you shift the gears or when you put your foot on the brake pedal has it ever occurred to you that tens of thousands of other drivers are doing exactly the same thing at the same instant and have you ever stopped to think that the brakes on your car must be more powerful than the engine because it actually takes more power to stop suddenly than to start gradually our ability to go swiftly has been made possible by the ability to stop safely each increase in driving speed has required an equal Improvement in the speed with which we can stop at this great Proving Ground men spend their lives just testing brakes finding out how to make them better to these drivers a car is just something to stop in a hurry or else weeks they spend and months and years easing on the brakes jamming on the brakes getting and stopping in a world of spinning wheels on concrete in mud and gravel and drifting dust what these men have learned about stopping automobiles on different Road surfaces with different loads and at different speeds has helped to give us the perfected brakes which are the greatest single factor that makes possible the speed at which we travel in safety today and the experience of these men proves that our own driving can be even safer if we know more about how our breaks work and what they can do for us here is a wheel from a modern motor car with a motor to drive it and the brake turned inside out so we can see exactly what goes on inside when you step on the brake pedal you force a hydraulic fluid to a cylinder in the brake mechanism the pressure in this cylinder squeezes a pair of brake shoes outward against a drum fastened to the wheel when the shoes rub against the drum they stop the wheel the shoes are pivoted on a set of lengths and hinges so they will wear evenly and stay in adjustment under all conditions due to the link Arrangement the rotation of the drum forces the shoes into tighter contact with much less effort on the part of the driver with these perfected hydraulic brakes we can stop in the shortest possible time regardless of the condition of the road and our speed naturally we can stop more quickly on a clean dry surface than on a wet slippery one if the wheels are completely stopped they lose their grip on the road and the car May skid under any conditions we can make the shortest stop when the wheels are allowed to turn just enough to keep their grip on the road now here is a test to show the effect of driving speeds on the stops we can make mounted on the running board of a car is this gun connected so that it will drive a steel Dart into a plank to Mark the road at the instant the brakes are applied the road is dry and clean so the wheels can get a good grip on it under these ideal conditions at 20 miles an hour it takes a little more than a car's length or about 20 feet to stop this car to stop with safety at 30 miles an hour we need more than twice as much room at 40 miles an hour we need 80 feet for safe braking distance thus we see that as the speed mounts up the stopping distance becomes rapidly greater a change of speed from 20 miles an hour to 30 miles an hour more than doubles the stopping distance at 40 miles an hour the stopping distance is again doubled and at 60 miles an hour the best brakes use up about 180 feet of road to stop the car under normal conditions remember that at any speed fast stops mean discomfort to our passengers we need to keep a clear stretch ahead of us so that we will have plenty of room to see what's in the road make up our minds step on our brakes and come to a smooth stop now suppose we let one of these Engineers tell us what they have learned about how to get the most out of our brakes for comfort and safety don't slam on the brakes when you want to stop use your brakes smoothly with gradually increasing pedal pressure and don't freeze on the pedal just before the car comes to rest why relax the pressure a little let the wheels catch up with the body for a smooth comfortable stop don't throw out the clutch as soon as you decide to stop let your engine help your brakes and wait until the car is almost at a standstill before you push in the clutch pedal and here's another tip from expert drivers at high speeds sudden braking tends to throw the car forward and lift some of the weight from the rear wheels so for emergency stops I get the feel of your car ease up on the pedal several times to let the weight of the car settle back and help the rear wheels keep their grip on the ground so they can do their part of the job of stopping the expert driver avoids emergency stops by using his brakes long before he has to don't apply the brakes on the turn slow down before you enter that curve and reduce your speed before you hit that stretch of wet pavement on very slippery roads use your brake pedal with a gentle pumping action now if you start to Skid release your brakes let your wheels get a fresh grip on the road then apply your brake smoothly give your brakes a break keep them adjusted know how they work and what they can do and use them with judgment at high speeds if we always keep that margin of safety we can travel swiftly ride comfortably and stop when we want to [Music]