Every tire is carefully inspected, and random samples are pulled for additional safety tests. As part of these tests, tires are x-rayed, cut apart and examined, run on test wheels, or road-tested to evaluate handling, mileage and traction performance. If properly cared for, tires can last a long time – usually from 40,000 to 80,000 miles, depending on the application.
As many as two hundred different raw materials combine into a unique mix of chemistry, physics and engineering to give consumers the highest degree of comfort, performance, efficiency, reliability and safety modern technology and creativity can provide. Here are the basic steps:
Planning and Design
Many tires are custom-designed to meet the stresses and performance needs specified by the maker of a particular model vehicle. The process begins with a computer, which converts the mathematics of the car’s special needs into specifications. A prototype tire is then made to test the tire design’s ability to provide the desired characteristics. Custom-designing a tire for a particular vehicle typically takes many months of testing, inspection, and quality checks by the tire maker and the vehicle maker. Only then does the vehicle maker commit with an order.
The production process begins with the selection of several types of rubber along with special oils, carbon black, pigments, antioxidants, silica, and other additives that will combine to provide the exact characteristics wanted. Separate compounds are used for different parts of the tire. A machine called a banbury mixer combines the various raw materials for each compound into a homogenized batch of black material with the consistency of gum. The mixing process is computer-controlled to assure uniformity. The compounded materials are then sent to machines for further processing into the sidewalls, treads or other parts of the tire.
Then the task of assembling the tire begins. The first component to go on the tire building machine is the innerliner, a special rubber that is resistant to air and moisture penetration and takes the place of an inner tube. Next come the body plies and belts, which are often made from polyester and steel. Plies and belts give the tire strength while also providing flexibility. The belts are cut to the precise angle and size the tire engineer specifies to provide the desired ride and handling characteristics. Bronze-coated strands of steel wire, fashioned into two hoops, are implanted into the sidewall of the tires to form the bead, which assures an airtight fit with the rim of the wheel. The tread and sidewalls are put into position over the belt and body plies, and then all the parts are pressed firmly together. The end result is called a “green” or uncured tire.
The last step is to cure the tire. The “green” tire is placed inside a mold and inflated to press it against the mold, forming the tread and the tire identification information on the sidewall. Then it is heated at more than 300 degrees Fahrenheit for twelve to fifteen minutes, vulcanizing it to bond the components and to cure the rubber. (FACT: This twelve to fifteen minute curing process is for passenger and light truck tires only, off-road and large tires may take up at a day to cure because of their size!) Every tire is then inspected, and sample tires are randomly taken from the line and tested. Some are x-rayed, some are cut apart to look for flaws, others are run on test wheels, or road-tested to evaluate handling, mileage and traction performance.