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How To Care For Your Car: Tires

January 3, 2020

What are tires?

Everyone knows the basics of what a tire is. However, most drivers don’t even think about their tires much until there’s a problem like a flat or blow-out. Tires are the single part of the vehicle that connects the car to the road, and their importance is frequently overlooked.

A huge amount of research and development goes into making tires that are long-lasting and provide excellent grip and traction on the road. The rubber compound and tread design used for a tire affects its longevity, grip, ride quality, noise level, and performance (not to mention its price). Nearly all vehicles (aside from sports/high performance cars) come with all-season tires from the factory. These tires strike a balance between the multiple benefits mentioned above. For many climates and vehicles, all-season tires are more than sufficient.

Some drivers may wish to install different tires based on the type of driving they do. For example, winter tires are designed to perform well in below-freezing temperatures and snowy conditions; this is accomplished by using a softer rubber compound and extra siping (the little lines in some tires’ treads that provide increased traction and tread flexibility in poor conditions). Studs can even be added to winter tires to provide traction on ice. On the other end of the spectrum, summer tires use a harder, smoother rubber that is designed for extreme traction and high performance. These benefits come at the cost of shortened tire life and poor (or even dangerous) performance under 40–50°F. There are also all-terrain tires available (an all-season tire with a “chunky” tread pattern, often used on trucks and SUVs) and mud-terrain tires (a more extreme version of the former, used for traction in mud, snow, and other adverse terrain). All of these specialized tires have their benefits for certain applications, but usually fall short in year-round, daily use.

Tires are available in countless sizes to suit all vehicles and wheel sizes. While all tires are constructed similarly out of multiple layers of steel and rubber, every vehicle has a specific tire size and load/speed rating. It is important to match these specifications when purchasing replacement tires (there are some exceptions to this rule, but they are few and far between in routine tire replacement). Standard tire sizing looks like this: 215/50R17 95V. The first number refers to the width of the tire tread, measured in millimeters (215mm in this example). The middle number is called the aspect ratio and is the “height” of the tire sidewall as a percentage of the width. In this example, this measurement equates to 50% of 215mm, or 107.5mm. “R” stands for radial, which refers to the construction of the layers of the tire. The third number in a tire size is the wheel diameter in inches. The tire in our example size would only fit a wheel that is 17 inches in diameter. After the tire size information is the load and speed rating. In the example above, 95 refers to a maximum load rating of 1521 pounds per tire (charts of different load ratings can be found online) and the V refers to a maximum speed rating of 149 MPH.

Another important item printed on the sidewall of a tire is the 10–12 digit DOT code. The last four digits of the code are the most useful: they tell the week and year the tire was manufactured. For example, “1316” means that a particular tire was made during the 13th week of the year 2016. A tire older than five or six years is recommended to be replaced, as the rubber begins to dry out and degrade (in severe cases it can even crack and expose the internal structural layers of the tire).

Why do they fail?

There are many different ways a tire can wear out or fail. Under normal conditions, a tire will wear evenly all the way to the minimum tread depth (2/32 of an inch). At 3–4/32” is when it is recommended to replace tires, especially when the vehicle is regularly driven in wet conditions (when the tread is low, there is less space available to channel water away from under the tires). If a tire is not replaced by the time it reaches the minimum tread depth, the result will be a loss of traction and eventual exposure of the secondary layers of rubber and internal steel cords — all of which equal unsafe driving conditions.

If the suspension or steering components are excessively worn or out of alignment, tires will wear unevenly. Under- or over-inflation will also cause uneven tire wear.

It is also important to address the cause of the wear, especially in the case of steering and suspension issues. If there are any worn components, those should be replaced in order to avoid the same wear pattern returning on the new tires. At the very least, an alignment is recommended with new tires to ensure the most even wear possible.

Another form of tire failure is a puncture. Punctures are most commonly caused by metal debris (such as nails) on the road. Luckily, punctures can often be repaired if conditions are right: the puncture must not be on the sidewall or in either outer strip of tread (there is too much flexing that happens in these areas and a patch will not hold). In the event of a puncture, it is important to stop driving as soon as loss of tire pressure begins (indicated by the TPMS warning light on newer vehicles, shown below). If a tire with low pressure is driven on, the internal structure of the tire can be damaged, rendering it unrepairable.

On vehicles produced before 2006, there is no tire pressure monitoring system, so the driver must pay more attention to the condition of their tires. If any abnormal noise or handling (such as pulling) is noticed, the tire pressures should all be checked. On all vehicles, if a tire with low pressure or compromised structure is driven on, especially at high speeds, there is risk of a blowout. This is when the tire suddenly ruptures and it can cause loss of control of the vehicle, resulting in an accident. Blowouts can also happen due to manufacturing defects, so it is important to inspect your tires or (have them inspected) regularly.

What if I don’t replace my tires when they are worn out?

As mentioned in the previous section, using tires past when they are worn out can result in unsafe driving conditions. There will be decreased traction, as well as increased braking distance and less stability in turns and while braking. In more severe scenarios, there may be a blow out if a tire is allowed to wear out far past its minimum tread. When a blow out occurs, the tire must be replaced before the vehicle can be driven (even if the spare tire is on the car, it should only be used for a limited amount of short trips until the tire can be replaced). Ideally, your vehicle will be maintained to allow tires to wear evenly and the tires will be replaced before they reach the minimum tread.

What do they cost, and why?

Inexpensive tires for smaller wheels can be purchased for as little as $60–100 apiece. Installation is usually around $15–25 per tire. However, vehicles with larger wheels and will require tires that are more expensive, simply due to the amount of material required. Tires for 18–20” (or larger) wheels can cost upwards of $200–300 per tire! There are also many different options when it comes to performance, tread life, and quality. More expensive tires will generally be rated higher in one or more of these categories, because more engineering and higher quality materials have gone into producing the tire. Specialized tires (such as mud-terrain, or summer performance tires) are generally more expensive for the same reasons.

There are usually a range of price points available for every tire size. However, price and quality generally correlate. Cheaper tires usually do not last as long and may be louder or less comfortable on the road. They may even handle poorly when compared to a more expensive tire. All of this is to say that spending less on the tires may require them to be replaced more frequently, cancelling out any cost savings. When choosing tires, it is important to take into account driving style and conditions, type of vehicle, as well as the driver’s budget and tire life expectations.

Is there anything I should replace at the same time?

When replacing tires, the technician will always install a new valve stem (where the air is filled) as well as new wheel weights when balancing the tire. If tires are being replaced due to uneven wear from faulty suspension or steering components, those parts should be replaced at the same time to prevent the same tire wear from returning. It is usually recommended to have an alignment performed when replacing tires, even if there are no problems — it will ensure the longest possible tire life is achieved.