Proper tires are vital for vehicle comfort, handling and safety. Tires are made for all vehicles at the consumer level, primarily passenger cars, minivans, performance automobiles, light trucks and SUVs. In addition, a wide selection of tires are made for motorcycles and scooters, competition cars and trucks, ATVs and all manner of commercial vehicles. Depending on their application, tires differ in terms of size, design, construction and performance characteristics.
Bias Ply vs. Radial Tires
While tire construction involves several other elements, one important distinction is bias ply vs. radial tires. Tires are built with rubber compounds strengthened by cords or plies contained within. Steel belts make up the skeleton of a tire, but the direction of the plies defines the type of tire. Bias ply tires feature cords that run at approximately +/- 60 degrees to the direction of travel, while radial tires feature plies that are stretched perpendicular to (or 90 degrees away from) the direction of travel. Radial tires are the most common type used today. They are beneficial in that the plies do not rub together, weakening them over time. Plus, radial tires directly improve fuel economy.
At a very general level, tires consist of a tread and sidewall. The tread is the circumferential aspect of the tire, all parts of which make contact with the road as the tire rotates. The sidewall connects the tread with the beads that encircle the rim. Tires are categorized according to the width of their tread, the height of their sidewall and the size of rim they are designed to take. They are also classified in terms of their speed rating and load index, known collectively as their service description.
Sizes and Specs
Tires are made to meet manufacturers' specifications as well as to provide upgrade options. Original Equipment fitments include tires installed at the factory. All vehicles specify the tire size(s) compatible with their make and model. With most vehicles, several size options are available.
A tire's specification is indicated on its sidewall. A common tire code reads as follows: P185/60R14 82H. This code tells practically all pertinent information about a tire:
- P stands for "P-metric," designating its use with passenger cars, minivans and some light trucks
- 185 is the section (tread) width in millimeters
- 60 is the aspect ratio, which tells the sidewall height listed as a percentage of the tire's width
- R is for radial construction
- 14 is the diameter of the wheel in inches
- 82 is the load index or maximum weight, in this case, 1,047 pounds
- H is the speed rating or highest recommended speed, corresponding to 130mph
All tires feature some type of code, although an assortment of codifiers are used. Another code format, 37X12.5R17LT, is common with certain truck/SUV tires. In this instance, the tire is 37 inches in total diameter, 12.5 inches wide, radial in design and takes a 17-inch rim. The "LT" at the end indicates the tire is made for light trucks useful in off-road or hauling applications.
Tires are primarily designed to provide traction on wet and dry surfaces. More than that, they must provide lateral stability when turning at high speeds, support the weight of the vehicle and its load and make optimal contact with the road. The tread pattern is the biggest factor in determining a tire's traction. Racing tires built for dry roads often have no tread whatsoever, allowing the full surface to grab the pavement. Consumer vehicle tires do not have that luxury, as they must account for wet, cold and/or snowy and icy weather. Tread patterns are computer-designed to channel water out and away from the tires in rain. Through a combination of grooves of variable width and depth, sipes or slits in the tread, ribs and blocks, tires achieve differing levels of traction and performance in all types of weather.
Standard passenger car, light truck and SUV tires are balanced for all-season use, providing stability, comfort and good traction in all weather, although light truck/SUV models are typically bigger and provide a measure of off-road traction. Performance tires offer added high-speed stability and responsiveness, while specialty off-road tires feature deep lugs and extra-thick sidewalls to bite into loose surfaces and provide more resistance to punctures. Winter traction tires may be pinned for studs or non-studded for maximum control and stopping power on snow or ice. Tire manufacturers utilize an assortment of technologies that affect design and construction. Among the most integral are tread compound materials, tread pattern, sidewall construction and internal belt and ply dynamics.
The quality of the road aside, weather is the most important factor that influences a tire's design. Because of seasonal changes in temperature and driving conditions, a variety of seasonal tires are available, suitable for use at all or select times of the year. All-season tires, as their name suggests, are useful year round, providing vehicles with good all-around traction and grip. Summer tires are built for dry-weather handling and performance, although standard models provide good wet traction as well. Winter tires are designed to provide traction on snow and ice, although the overall selection varies widely. All-terrain tires are built for light trucks and SUVs and are made to provide on-road traction while offering fair to good off-road capabilities.
Specialty tires include those specifically designed for off-road mud, rock or sand driving and ultra-high performance, as well as non-street legal racing tires and trailer tires. Specialty tires are built primarily to do one thing, from climbing over loose rocks or through muddy ruts to making high-speed turns on a dry tarmac track. As a trade-off, specialty tires are often illegal on public roads as well as being almost useless on wet or snowy surfaces.
Brands and Prices
Numerous tire manufacturers exist, offering a wide selection of tires of all types. Some companies make specialty tires, while others have a diversified product line. Still others primarily produce models for the consumer passenger car and/or light truck market. A short list of tire brands includes these:
Costs for tires vary widely. A single tire can cost $50 or less. High-performance and specialty tires can cost several hundred dollars apiece or more depending on the maker and application. Some tires, including high-performance and maximum traction winter tires, deep-lugged mud tires and others should always be used in full sets. With standard touring tires, mismatched sets are often allowable.