The tires on your car perform a function that is far more critical than most people think. They are all that separates your car – a 4500 lb steel cage moving fast with people inside – from the road surface. Not only that, the brand and type of tires on your car will affect the handling and feel of your car when you drive. Does this seem like a bit of hyperbole? After all, aren’t most tires pretty similar? Well, in some ways they are but most have quite different characteristics. Let’s take a look at how tires are made and you’ll see that there are quite a few components in each one.
Tires are made up of four major components: Beads, Cords, Steel Belts, and Tread. The beads are the circular part of the tire that sits on the wheel rim. Beads are a loop of high-strength steel cable coated with rubber. Cords are layers of polyester cord that form the body of the tire. The cords in a radial tire run perpendicular to the tread and diagonal bias tires have cords that run at an angle to the tread. Cords are coated with rubber bond to hold them together. Sometimes manufacturers put fine steel wires into the cord assembly for extra toughness. Finally the tread is the outside of a tire and is made from a mixture of many different kinds of natural and synthetic rubbers.
All of the major components as listed above are assembled in a tire-building machine. This machine ensures that all of the parts are in the correct location and then forms the tire into a shape and size fairly close to its finished dimensions. The tire is then heat cured in the machine. This process is called vulcanizing and it bonds all of the tire’s components together. When cooled, the tire is removed from the tire machine and goes through a thorough inspection process before it is shipped to dealers.
What the numbers mean
So, what exactly what was built in our tire-building machine? Thanks to Kindle Autoplaza of Cape May Court House, a local Ford, Lincoln, Chrysler, Dodge, Ram, Jeep dealer in Cape May Court House, NJ, we’ve got the scoop. The answer is encrypted in the numbers on the sidewalls. Let’s consider a tire that is has the marking: P215/65R15 99H on the sidewall.
Tire Type – P designates that the tire is a passenger vehicle tire. LT is used for a light truck tire and T is for a temporary or spare tire.
Tire Width – The number 215 is the width of the tire in millimeters (mm), measured from sidewall to sidewall. Since this measure is affected by the width of the rim, the measurement is for the tire when it is mounted and inflated on its rim.
Aspect Ratio – The number 65 designates the aspect ratio. Basically this number determines how fat or narrow a tire’s profile is. This aspect ratio is calculated by measuring the height of the tire, from the bead to the top of the tread, and dividing it by its width. The result is a percentage, as in 65% in this case. Note that the smaller the aspect ratio, the wider the tire is in relation to its height – the fatter it looks.
Tire Construction – The R designates that the tire was made using radial construction. Older tires were made using diagonal bias (D) or bias belted (B) construction.
Rim Diameter – 15 specifies, in inches, the wheel rim diameter the tire is designed for.
Uniform Tire Quality Grading (UTQG) – The 99H is a grade that this specified by the uniform tire quality grading (UTQG) system. You can check the UTQG rating for your tires on this page. Your tire’s UTQG rating tells you about three things: How quickly the tread wears, the traction you can expect and maximum temperature the tire should be operated at.