Your tires are one of the most important elements of your car. They are the only component that comes into contact with the pavement, and they play an important role in safety, fuel economy and a smooth ride as well as how the car handles. Selecting the right tires — and maintaining them throughout their life — is a critical part of getting the most out of your driving experience.
However, there are so many different types of tires available that the task has become more complicated than ever before. Whether you are a new driver who knows little about tires or you are merely curious, the following information may be of interest to you.
The Parts of a Tire
Depending on the brand and model, your tires may be composed of natural and/or synthetic rubber, metal wire, fabric, carbon black and other chemicals. Different parts of the tire can require different combinations of materials to provide longevity, traction, superior handling or strength. The basic parts of a tire are as follows.
- The tread is the area that makes contact with the pavement. Most tread patterns are specific to a manufacturer and/or model of tire. Over the years, manufacturers have conducted extensive research to find the best tread patterns to address specific issues, such as the best pattern to prevent hydroplaning on wet pavement or the pattern that offers the smoothest ride.
- Tread voids and rain grooves are two different elements, but they perform similar functions. Their main purpose is to channel water away from the tread, thereby improving traction. However, tread voids also allow the contact surface room to flex slightly as the car is moving, allowing more of the tread to make contact with the pavement.
- The bead of a tire is the part that is in contact with the rim. The bead is typically made from relatively rigid, high-strength rubber with steel wire reinforcement. The bead forms a tight seal to prevent air leakage and to keep the tire from shifting on the rim.
- The sidewall is the part that connects the tire’s bead and tread. Sidewalls are normally made from rubber that has been reinforced with steel cords or fabric to provide greater strength. Mandatory warnings and manufacturers’ codes can be found on the sidewall.
- The tire’s shoulder is the area where the tread transitions to the sidewall.
- Plies are essentially the same as layers. In tires, plies are made from stiff cords, which are made from steel, nylon, cotton, Kevlar or silk and encased by elastomers made from rubber, carbon black or other compounds. The plies play an important part in helping the tire hold its shape.
Types of Tires
Manufacturers produce three basic types of tires for passenger vehicles.
- Bias ply tires are sometimes referred to as cross-ply tires due to their construction. These tires have cords that run diagonally between the beads at an angle of 30 to 40 degrees, with each additional ply set at a different angle to form a crossing pattern beneath the tread. The primary advantage of bias ply tires is a smoother ride on rough pavement; the primary disadvantages are less traction and a reduction in control at high speeds. They also offer more “rolling resistance” or drag.
- Belted bias tires are essentially cross-ply tires to which steel or fiberglass belts are added during construction. The belts increase the stiffness of the tread, reducing the rolling resistance common with traditional bias ply tires.
- Radials are constructed with parallel cords that are approximately perpendicular to the tread’s centerline and topped by steel or cord stabilizer belts. Radials offer reduced rolling resistance, a longer tread life and better handling. However, on rough pavement at lower speeds, they can also yield a harder ride.
Regardless of the tire type, manufacturers use a tire-building machine to assemble all of the components into what is known as a green tire. Although the tire has the basic size and shape of the finished tire, the components are not as secure as they will be after finishing. It also does not yet have a tread pattern or other markings. The bonding of the components and the addition of the tread pattern and other markings happens in a curing machine in a process known as vulcanization.
What Tire Markings Mean
Manufacturers include two codes that are molded into the tire’s sidewall. These codes provide information on the tire’s specifications, intended use, manufacturing location, mold number and more. One set of letters and numbers is called the DOT code and is easily recognized as it begins with the letters, “DOT.” The information following these letters represents data related to the manufacturer, such as where, when and by whom the tire was made.
The second code is more complex and of greater interest to consumers. The best way to explain how to interpret the code is to break down a typical code, such as P215/65R15/95H M+S.
- P — Passenger vehicle. (Other designations are LT for light truck and T for temporary space-saving spare.
- 215 — The width in millimeters at the tire’s widest point.
- 65 — Called the aspect ratio, this number represents the ratio of the sidewall height to the tire’s width.
- R — This stands for a radial tire. An “B” in this position would designate a bias ply tire, and a “D” would stand for a diagonal bias tire.
- 15 — This tire is made to fit 15-inch rims.
- 95 — The load index, or the maximum weight per tire, is represented by a number ranging from 60 to 125. A load index of 95 means that the tire is rated for a maximum of 1521 pounds per tire.
- H — The tire’s speed rating is the maximum speed for which the tire was designed at its load index. An “F” is rated for a top speed of 130 miles per hour.
- M+S — This stands for “mud and snow,” which is considered an all-season or winter tire. Other designations that manufacturers can use include M+T (mud and terrain), TL (tubeless), XL (extra load) and WSW (white sidewall).
Manufacturers can also mark their tires with other information, such as the expected mileage the tires may obtain under normal use and with proper maintenance or the tire’s temperature tolerance. There may also be an AA, A, B or C marking that indicates the tire’s traction rating, with AA being the best rating.
Different Styles of Tires
When shopping for tires, you will notice that manufacturers use a variety of terms to describe different styles. Tires that are most suitable for specific conditions, such as winter driving or off-road use, can be identified by the term used by the manufacturer. Different tread patterns, materials or tread voids can provide different levels of traction, help the tires shed mud or otherwise enhance performance under specific conditions. The most common terms are:
- All-season: These tires are designed to function adequately year-round. However, they will not perform as well on snow-covered pavement as a winter or snow tire will perform.
- Snow: Snow tires may also be referred to as winter tires or mud and snow tires. Their tread is designed to help the tires shed snow, water and mud, but they are typically unsuitable for driving on warm, dry pavement.
- High-performance: These tires are designed for “sporty” driving at higher speeds. Their tread is typically a softer rubber to improve traction, particularly when cornering. The treads often have shallower rain grooves, which can decrease their performance on wet pavement. In addition, the softer treads normally provide a shorter tire life. These tires are sometimes referred to as “summer” tires.
- All-terrain: All-terrain tires are common for light trucks, SUVs and other vehicles that may traverse rough roads or be taken off-road. The sidewalls are normally stiffer to offer increased protection against punctures, and the tread patterns are usually spaced wider than an all-season tire to help shed mud, gravel or water.
- Low-profile: Low-profile tires have wider heads and shorter sidewalls than traditional tires made to fit the same rim. These tires are designed to improve performance and handling, but they usually provide a rougher ride than traditional tires.
- Spare: A spare tire may be a full-sized tire that is identical to the four on the car, or it may be a space-saving “mini-spare” that is designed to be a lightweight, temporary replacement. Most space-saving spares have restrictions on the maximum speed or distance for which they are safe, while full-sized spares function like any other tire.
Maintaining Your Tires
Tire maintenance typically falls into one of two categories: maintaining proper tire pressure and rotating the tires. Neglecting either of these can affect your stopping distance, handling, ride and fuel efficiency as well as decrease the life of your tire and its load-bearing ability.
The tire pressure marked on a tire is the maximum pressure that the tire can withstand. The optimal pressure depends on a combination of factors, such as whether the tire is on the front or rear, the load it must bear and the temperature. On newer cars, the range for tire pressure can be found on a plate mounted inside the driver’s side door. This plaque may be mounted in other locations on older models. The information can also be found in the owner’s manual.
The best way to check tire pressure is with a manual gauge. This is true even if your vehicle has a monitoring system for tire pressure; these systems normally do not warn you until pressure is at least 25 percent below specification, which means it is already in the danger zone. Remember to check your spare’s tire pressure as part of the procedure.
All four tires on your car will not wear in precisely the same pattern at exactly the same time. However, cars perform best when all tires are achieving the same traction and turning at precisely the same speed. Rotating your tires every 3,000 to 7,000 miles can help keep all four tires synchronized.
It is also an ideal opportunity to check for uneven tread wear that could indicate a mechanical problem. Your owner’s manual will state how often tires need to be rotated. It will also tell you what the rotation pattern should be; for example, the pattern may be for the driver’s side rear and passenger side front to change places. If you have the rotation done by a shop (as opposed to spending the time and effort to do it yourself with a single bumper jack), the technician can also balance the wheels to reduce uneven wear or vibration.
How Long Tires Last
Giving an accurate estimate on the life of a tire is difficult. Most tires on the market today are rated at 40,000 to 80,000 miles, but that number is based on a properly maintained tire that is on a car driven under normal conditions and that does not incur any damage, such as a puncture.
There are numerous factors that can affect the longevity of your tire.
- You can shorten the life of your tire if you make frequent hard stops, “burn rubber,” overload your car or fail to maintain proper tire pressure.
- The roads you travel can affect the life of your tires. If you drive a highway riddled with potholes at 55 miles per hour, your tires probably will not last as long as if you drove only on well-maintained city streets at 40 miles per hour.
- Road hazards can damage tires so badly that they cannot be repaired.
- The climate in which you live can play a part in the longevity of your tires. Extremely hot or cold temperatures can cause your tires to age prematurely.
When to Replace Tires
Unlike many other parts of your car, your tires will need to be replaced periodically. To avoid becoming stranded and to ensure that your car can be operated safely, you should replace your tires whenever one of the following occurs.
- Replace your tires when the tread is worn to or below the depth recommended by the manufacturer, even if the tread wear pattern is even. The specific depth varies by the model of tire.
- Replace your tires if the wear pattern is extremely uneven, but first, determine why the tires are not wearing evenly and have the problem corrected.
- Replace any tires that have been damaged too badly to be repaired or that have become deformed. For example, a puncture can often be repaired, but if the puncture deformed the belt or cords, you should replace the tire.
Your car’s tires are too important to ignore. Select the best tire for your car, take care of your tires and enjoy the ride.
Now that you know all about tires, what type of tire do you think you will buy for your car, and what features will have the greatest impact on your decision?