A dramatic difference between trucks and cars is that trucks take much longer to stop. Trucks with properly maintained brakes generally take 25 to 65 percent longer to stop than a car, which translates into a 60 to 80 percent braking efficiency depending upon the load.
Passenger vehicles such as cars, light trucks or SUV's use a hydraulic braking system. When the driver pushes on the brake pedal it in turn pushes on a hydraulic cylinder: the cylinder then sends pressurized brake fluid to the hydraulic pistons on the car’s wheels. These pistons engage the brake pads, which then press against metal surfaces and slow the car down.
The hydraulic brake system is not suitable for 18-wheelers because the trailer must be frequently connected and disconnected from the tractor. Additionally, the larger scale that would be needed for the system to work on the much larger trucks would not translate well. Instead of a hydraulic brake system, 18-wheelers use compressed air and an air brake system.
When a truck driver presses on the brake pedal, it causes compressed air to move from a storage tank through various hoses and into the brake chamber. The air then forces out a rod that pushes against the slack adjuster. This causes a camshaft to turn, which twists an S-shaped piece of equipment known as the S-Cam. This makes the brake linings come into contact with the brake drum, thereby creating friction and slowing down the truck.
To function properly, the truck’s air braking system must perform several important tasks. It must keep a steady flow of compressed air, and it must direct that air’s flow. It also must convert the energy in the air pressure into mechanical force to stop the truck.
One big advantage of air brakes is that they are reliable. Most big rig trucks also feature a dual brake system; if one system fails, the other system kicks in. However, air brakes also come with some significant drawbacks.
One primary factor to consider in any truck accident is brake lag time. The two kinds of brake lag are mechanical lag and air-pressure lag. All brake systems have mechanical lag, or a slight delay in the buildup of brake force after the brake pedal is applied. Air brakes, however, have an additional delay related to the build-up of air pressure: the time that it takes for the air to travel from the air tanks to the brake chambers, and to build enough pressure to generate brake force.
The brake lag in big rig trucks is relatively small—approximately a second or less. But, as anyone who has ever been involved in an emergency situation knows, a second can have a significant impact on whether or not the vehicle is able to stop. This problem is compounded by the massive increase in size of 18-wheelers; this creates extra momentum that needs to be overcome before the truck can stop. The result is that large commercial trucks having a stopping distance approximately 40% further than passenger vehicles, and that’s if the driver has quick reflexes.
These increases in stopping distance may also be partially attributed to the tires used on trucks. Truck tires are made from very hard rubber so they will last much longer than car tires. However, this feature causes them to generate lower friction values than the softer-compound car tires.
If you have been involved in an accident that was someone else's fault, contact Brent Cordell today for a free initial consultation.