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Tires
The Parts of a Car Tire
Tires have a lot more engineering in them than you might expect. Here are the main parts.
Tread
Most people are familiar with this. The tread allows the tire to conform and grip the road surface, channel water out of the way and dissipate heat. In the U.S., depth is commonly measured in 32nds. While measurements vary, most passenger car tires start with about 9/32 to 10/32 of an inch of tread, and reach the end of their usable life around 2/32 to 3/32.
Sidewall
The reinforced rubber on the side of the tire between the tread and the wheel rim. The stiffness and size of this area will have a huge impact on the car’s ride and handling characteristics.
For example, high performance cars may be equipped with tires with stiff, short sidewalls to prevent flexing during hard cornering and give maximum grip, while those on a passenger car or truck may use a taller and more flexible sidewall to improve ride comfort. This is also where all the information about the tire is printed. (See Car Tire Markings, below.)
Bead
A rigid core of rubber with a reinforced steel cable running through it where the tire meets and seals against the wheel. While early tires had inner tubes (like bicycle tires), the bead in a modern tire provides the airtight seal against the wheel.
Wear indicators
These are thin lines of raised rubber running between and perpendicular to the tread rows. When the tread wears down to a point where the individual tread blocks/rows are even with these indicator bars, the manufacturer feels the tire has reached the end of its usable life and should be replaced.
Note: Most tires should be replaced before the tire reaches this level for maximum safety, especially in wet conditions.
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Internal construction
Most people have heard the term “steel-belted radial.” This is the most common type of tire produced, with braided steel belts inside the tire under the tread layer to provide structural strength, puncture resistance, increased tire life and traction. Below this are crisscrossing plies of nylon or other materials to provide additional strength around an inner layer of rubber which seals in the air.
For more detail, check out the U.S. Tire Manufacturers Association.
Types of Car Tires
- All-season tires;
- Snow tires;
- Summer performance tires;
- No directional vs. directional tires;
- Racing/off-road tires.
Car Tire Markings
The side of a tire gives you a lot of information about its size, intended use, anticipated life and age.
Size
Each of the numbers in a tire size means something specific. For example, 225/65R17 means the tire is 225 mm wide, has a sidewall that makes it 65 percent as high as it is wide and fits a 17-inch wheel.
Tread wear
This is almost useless number since there are no uniform regulations on what it means. It simply indicates of what the manufacturer expects from the tire — the higher the number, the longer the expected life. It is most useful comparing multiple tires from the same brand. For example, a 400 tread wear designation means that they expect that tire to last four times as long as one with 100 tread wear.
Age
A small oval-shaped indent with numbers inside tells you when the car tire was made. You may have to check both sides of the tire to find the one with the age. Called the Tire Identification Number, it has been required since 2000 in a standard format that includes the week and year as the last four digits.
For example, a number inside the oval ending in “2319” means it was manufactured during the 23rd week of 2019. Because tires are subject to oxidation (dry rot) as they age, this number lets you know exactly how old the tires are.