|Mike Byrnes and Associates, Inc. Bumper to Bumper: The Complete Guide to Tractor-trailer Operations. Texas: New York: Barron's Educational Series, 2003.||"If anything goes wrong with the trailer system that causes it to lose air pressure below around 20 to 45 psi, a spring in the trailer air supply valve on the dashboard pops the red knob out."||138–310 kPa|
|Obtain The Best Results From Your Tires. Titan Tire Corporation||"To assure fully-seated beads, inflate tire to 35 psi inflation pressure using a standard air line, and then with valve stem at the top, bleed pressure and excess water or solution down to 1-2 psi above recommended inflation."||241 kPa|
|Lang, Michael. Commercial Motor Vehicle Tire Pressure Sensors. U.S. Department of Transportation, Federal Motor Carrier Safety Administration, July 2005.||"As a group, for-hire carriers sampled had 7.01% of all tractor tires underinflated by 20 psi or more. In contrast, the private carriers sampled had 13.21% of all tractors tires underinflated by 20 psi or more."||> 138 kPa|
|"Tire." The World Book Encyclopedia. Volume 19. Chicago: World Book, 1984.||"In 1922, low pressure tires, or balloon tires, were introduced. They held from 30-32 pounds per square inch (2.1 to 2.2 kilometers per square centimeter) of air pressure."||207–221 kPa|
|Farmers Can Save Big Money on Fuel. AgTech Innovator, 28 May 2007.||"Never exceed 35 psi (241 kPA) inflation pressure, as severe damage or personal injury can occur should the tire separate from the rim."||< 241 kPa|
Tractors are used to pull heavy loads of many different kinds of things. They are designed to move at slower speeds than automobiles that are used for transportation. It is used a lot for construction and agriculture. Without it, a fruit farmer would not be able carry loads of watermelons to sell for their business or a construction worker would not be able to carry tons of concrete to their work site. Tractors contribute in giving a large source of power and save time in various tough situations.
What keeps tractors going are man's greatest invention: the wheel. They are mostly made out of rubber and are pneumatic (filled with compressed air). This helps support the weight of the vehicle. The pneumatic tire was invented by Robert W. Thomson, a Scottish engineer in 1845. He created tires that gave smooth rides but they were not strong enough. The invention was improved by a Scottish veterinarian named John B. Dunlop. Years later with its enhancement, the correct amount of air pressure and a few adjustments to the air-filled tubes (tires), automobiles were able to travel smoothly and the wheels were strong enough to hold them up.
To keep its steadiness and strength to act on its duty, wheels of tractors have a pressure between 138 kilopascals to 310 kilopascals. This becomes the application of force to something by something else in direct contact with it. The SI unit for pressure is pascal (Pa) but Americans use the unit psi (pounds-force/square inch).
Suzanna Zhou -- 2007