Understanding Tires: Specs, Wear, & Making The Right Choice For Your Car

At FCP Euro, we know a thing or two about what it takes to keep your car on the road. Careful and fastidious maintenance can help your vehicle perform better and stronger and ensure it is road-ready every day for years to come. From where to start when selecting a snow tire, to the most comfortable option on your commuter, to the most aggressive tire you can run on the weekends, we're here to help you decide which tires are best suited for your vehicle and purpose.

When it comes to routine maintenance, the consumer is spoiled for choices when shopping for parts. Pending the aim of the project, parts such as brake pads or cooling systems can range from the same design the original manufacturer of your vehicle sold to some of the most premium options for performance driving on the market. But regardless of whether parts are purchased to restore its function or shoot for a win in competition, one fact remains the same across any and all vehicles; without the correct choice in tire, a vehicle will never live up to its potential. 

The market for tires is a flooded one, with hundreds of tires to choose from across nearly as many manufacturers. Tire shopping can be overwhelming and confusing, and shortcomings of an incorrect choice can vary from excessive road noise in a daily driver built for silent cruising, to losing control of the vehicle on a cool evening.

The Right Tire For The Situation

There is no better feeling than pitching a car into a corner on a warm summer day, and feeling the front end float, settle, and bite as a quality tire grabs hold of the pavement, gravel, or circuit. Conversely, there is no worse feeling than leaving for a commute on fresh-packed snow and being unable to make the jump from the driveway to the street without a push from passerby. For any environment, there is a type of tire to achieve the best results. As a result, most tires are generally broken into these categories:

• All-Season 
• Summer/Performance
• Off-Road/All-Terrain
• Track/Competition
• Winter/Snow

While most of these categories are fairly self-explanatory, determining which category is necessary is the single most important step when selecting a tire. A good set of summer tires, for example, will provide excellent grip and engagement during aggressive street driving in higher temperatures. However, by simply altering an environment slightly, the outcome differs; move a summer tire to a track, and the excessive heat and friction created from aggressive driving will eventually cause the rubber to overheat. Commonly known as a tire getting “oily,” the grip enjoyed in everyday driving on a good summer tire can fade to aggressive understeer in as little as a single lap, as the surface of the tire becomes too hot to maintain its structure and fails to grip. Driving at excessive temperatures can also lead to “blistering,” as the surface of the tire becomes too hot and begins to deform. 

Conversely, drive an aggressive track tire on a cold fall evening (or even a rainy spring day) and that tire may be unable to get up to temperature. A track tire may additionally hold a tread pattern too aggressive to properly channel rain out from underneath the rubber, leading to a loss of traction even when driving in a straight line. Both can ultimately produce a shortcoming of grip well before the expected limit, and rain can make a simple commute a true fight in the driver’s seat.

Consider the environment the vehicle will be driven in. In a track or autocross setup, a summer tire will never fully achieve the potential of a proper competition tire. In a vehicle destined to travel across dirt and gravel, an off-road design will make significantly more noise as the chunky pattern thumps along a public street or highway. A common compromise across most tire types is an all-season tire, which aims to bridge as many gaps as possible; an all-season will never be excellent at one task, but will accomplish most with more grace than a targeted tire.

How to Read Tire Size

Tire shopping presents a consumer with a lot of numbers. Much like a proper article of clothing, it is important to assume all attributes align to ensure the best fit. The numerals along the sidewall of a tire can present a good deal of this information at a glance.

This set of summer tires will serve as a reference. First, the dimensions of the tire must be assessed.

• Tire Width: 205 millimeters
• Aspect Ratio: 50%
• Diameter: 16 inches

Presented simply as “205/50R16,” we learn a lot about this tire. The first number will reference the width of the tread pattern, where the vehicle meets the road. The width of a tire can greatly influence a handful of traits.

• Grip
• Fuel Economy
• Ride
• Cost

A wider tire will have more surface area to make contact with the road (also referred to as a “Contact Patch,”) meaning more grip will be available than a narrow tire. However, as a direct result, other performances suffer. As more of the tire makes contact with the road, more friction is created for a vehicle to overcome. The rolling resistance of the larger tire will require more effort from the vehicle to produce forward motion, whereas a narrower tire will promote fuel economy. Additionally, while a wider tire may straddle bumps and uneven surfaces more evenly, promoting a smoother ride, the additional amount of material needed to manufacture a bigger tire will directly influence the investment cost.

Tire sizes can easily be browsed through various tire size charts found across the internet, but shoppers must be aware that too tall or too wide of a tire can result in rub against suspension or fender components. This can result in damage to vital suspension components as the tire makes contact during turn-in, and as tires grab a fender or body piece during load, wrinkling or rippling can occur to body panels. Changing the tire's diameter may also result in a variation in rotation per mile driven, meaning speedometers (and odometers, by association) may read less accurately than when using the tires sold by the manufacturer. Additional resources can be found online to form a direct comparison between tire sizes.

Aspect Ratio

The second number, the tire aspect ratio, is a percentage indicating the width of a tire's sidewall. In the given example, we see “50” presented. This notes that the sidewall of the tire represents 50% of the width of the contact patch. Mathematically, it can be deduced that if this tire is 205 millimeters wide, this tire's sidewall is 102.5 millimeters wide.

Sidewall width also greatly affects the traits of the tire.

• Grip (via sidewall roll)
• Comfort
• Cost

Again, the use of more material will generally lead to an increase in price. However, discussion about sidewalls raises the conversation of sidewall rollover.

As a tire grips, the rubber flexes and readjusts itself quite heavily. Ultimately, the goal of any tire is to have a suitable contact patch at all times. When a tire loses hold of the road with its contact patch, oversteer or understeer occur. The sidewall is directly influential in this element, as the sidewall's size determines how much the contact patch can shift under hard load. 

A smaller sidewall will generally be more suitable for performance driving, as the compact and stiff nature will prevent the contact patch from moving excessively. However, it will also greatly strengthen the tire’s integrity, meaning the rubber will be less flexible over bumps and debris. A pothole or dip in the road will likely be felt and heard on a tire with a small sidewall, while a larger sidewall will help to absorb a good deal of the shock. A larger sidewall can also extend the life of suspension components by taking some of this impact away.

In a case of excessive sidewall rollover, grip is compromised. A large sidewall forced to corner hard can roll heavily enough to shift the contact patch from exclusively on the tire's tread onto both the tread and the sidewall. As the sidewall is structural and is not for performance, grip will be compromised greatly at this limit. In motorsport and competitive driving, this can be battled by altering tire pressures to increase the tire's rigidity. Still, premature wear and loss of traction can occur as a result.

Wheel Diameter

The third number refers to the diameter of the wheel which the tire is sized for. In this case, the vehicle fitted with these summer tires has a 16-inch wheel. The tire is sized appropriately to ensure that all of the aforementioned characteristics are applied as they have been engineered to do. 

Load Rating

Finally, at the tail end of these digits, we see a notation of “87W.” The numerals represent the tire’s load index, while the letter “W” denotes tire speed rating. 

Load index informs the buyer of the load capacity of the tire. In this individual case, a load index of 87 references a carrying capacity of 1,201 pounds for this tire. This tire will be sufficient until a greater amount of weight than this value is applied.

Speed Index

The speed index of a tire references the peak speed capability of the tire before failure becomes a possibility. In environments where speed limit is not a factor, such as in a racing environment or on German highways, a high speed index can be the difference between comfortable high-speed cruising and losing a tire at speeds too high to recover. In this case, a Speed Index of “W” denotes a limit of 168 miles per hour. This is the maximum rotational velocity this tire can withstand before its structural rigidity is compromised.

In the instance of an altered wheel size from what was originally sold on a vehicle, a lowered car looking for stretched tires, or a driver looking to add as much tire to a wheel as possible, a tire size calculator can be used to ensure a proper fit. A host of websites are available across the internet to take the guesswork out of selection, and with simply the knowledge of the tire dimensions mentioned above will provide proper parameters for operation.

How To Read Tire Ratings

Next, the additional information of this tire must be considered. The traits of the tire are broken into these categories, and are referred to as “Uniform Tire Quality Grade” standards:

• Treadwear: 340
• Traction: A
• Temperature: A

Treadwear

Treadwear ratings are based upon data gathered by tire manufacturers in simulated testing. Upon completing a cumulative 7,200 miles of driving, the tire is assessed for wear and is assigned a rating. A rating of 100 would reference that the tire can be expected to last as long as the tire during testing, while a rating of 200 would indicate the tire would last twice as long in an environment free from simulation. In the case of the summer tires being observed, the treadwear rating is 340. With a proper alignment, utilization of recommended pressures, and appropriate tire rotation, these tires can last more than 3 times as long as a 100-rated tire. Compromise on the production side to achieve this can be reflected in a harder tire compound, meaning less grip when heated. 

In the world of motorsport, treadwear is one of the more important ratings to pay attention to. As these directly reflect the compound a tire is made of, grip is directly affected by the treadwear rating. In racing, tires are often referred to as “soft” or “hard.” A soft tire will likely have superior grip, but will sustain its performance for less cumulative mileage. As such, an aggressive performance tire or a track tire will likely see a significantly lower treadwear rating, indicating a shorter lifespan, but more grip.

Traction Rating

Traction ratings are largely utilized during tire testing to assess the quality of the tread compound. These tests are simulated over wet asphalt and wet concrete to assess the quality of grip during hard braking on a slick surface. A letter rating is then assigned to the tire, indicative of the range of g-forces sustained under braking. The example tires provided have a traction rating of “A,” and are able to sustain a stopping force of over 0.54G on wet asphalt and 0.38G on wet concrete. This would indicate above-average performance in wet conditions.

Temperature Rating

The final metric utilized is a temperature rating. Simulated tires are assessed for their ability to build and dissipate heat while operating at high speeds. A letter value is again assigned to indicate the speed of which the tire can operate before heat failure may occur. The provided example tire has a temperature rating of “A,” so the tire can withstand heat generated by friction at over 115 miles per hour.

Date Codes

Tire date codes are a final and necessary check before purchase. Often most heavily considered upon the pending purchase of a pre-owned vehicle, tire date codes serve as a date listed to ensure a tire's efficacy before integrity may become compromised. The tire date code is listed on a tire's sidewall in a “Week/Year” format. 

Symptoms of a tire that is expired can include excessively dry rubber or cracking, and will often lead to leaking of air and eventually complete failure as integrity becomes compromised. With an out-of-date tire, all of the benefits of selecting said tire are null-and-void; performance will be greatly hindered, and driving on an expired tire can be hazardous.

How To Read Tire Wear

When inspecting a used tire, there are additional indications of wear beyond the date code that ensure its integrity. Buyers should inspect the sidewall, edge of the tread, and in between the grooves of the tread for any cracking (also commonly denoted as dry rot). This is often seen on a vehicle that has been stored for an extended period, and while the tires may present themselves as new otherwise, a dry-rotted tire will require replacement to ensure safe operation.

Tread Depth

The depth of the tread can be examined at the same time. Tire tread depth is measured in thirty-secondths of an inch, and a new tire will generally be produced with around 10/32 of tread depth. Utilizing a tread depth gauge, a buyer can determine how much of the tread pattern remains before a vehicle may become hazardous to operate in wet or snowy conditions. A tread depth gauge is incredibly simple to use, and requires insertion of the tool into the most shallow of the grooves on the tire for measurement. Generally, as low as a depth of 6/32 inches is considered acceptable, whereas any measurements producing less than this amount will indicate replacement prior to driving in snow conditions. At 4/32 inches, wet weather performance may also become hazardous.

Suspension/Alignment/Setup Related Wear

Following examination for tread depth and dry-rot, the wear of the tire can be assessed. Not only does tire wear inform a buyer of the cost of investing in the vehicle to indicate tire life, but it can also serve as a crucial indicator towards damaged or failing suspension components.

As suspension components age and fail, the vehicle's alignment may be altered as play is introduced into the suspension assembly. Altering suspension alignment in the form of toe or camber will be directly translated to the tire and the effect of how it wears. Vehicles with less tread depth on the side closest to the cabin, for example, are likely being driven with excessive negative camber.

A buyer can form the assertion that in addition to needing a new set of tires, a worn bushing or mount will likely be located somewhere within the suspension assembly. These will need to be repaired immediately, as both worn suspension components and uneven tire wear can result in unsafe operating conditions for daily operation. It is for reasons like these that we take pride in being able to offer our Lifetime Replacement Guarantee, as wear and risk associated with failing suspension components can be negated as they occur.

In extreme cases, uneven tire wear can be observed with the naked eye. The tread pattern will appear more worn on one side of the tire, and cords of the tire may be visible through the rubber. These tires will need to be replaced immediately to ensure safety of operation. The tire below demonstrates both camber wear and toe wear.

In less extreme circumstances, the tire gauge can serve as a vital tool to observe data. Tread depths can be measured across all channels in the tire, and can be compared for variation. A tire with less tread depth towards the middle of the tire has likely been overfilled, the increased volume of air resulting in the middle of the contact patch sustaining more rolling friction than the rest of the tire. An underinflated tire may have the opposite effect, as the inside and outside of the contact patch stretch and grab with the undulations in the road.

What Tires Are Right For You?

Your car, location, environment, driving style, and your overall intentions with your vehicle will help determine what tires are right for you. Without knowing every variable, there is not one correct choice. Once you've determined these, consulting the reviews of other buyers is typically the next step. These reviews can be located across many mediums of the internet in the form of published expert reviews as well as consumer ratings, so be sure to acknowledge subjective data in addition to the objective data that this guide provides. Tire Rack has one of the best tire selections with a long list of user reviews on each tire. 

With all of this knowledge, then a choice in tire can be made. Some examples scenarios are:

• A BMW serving as a commuter in the northeastern United States. For the majority of the year, an all-season tire will suffice in all conditions. A larger sidewall with a moderate treadwear rating will ensure comfort as well as quiet operation, while also maintaining fuel efficiency. In the case of a rear-driven vehicle, a second set of snow tires may be preferred. If this is unobtainable, an all-season option targeted more towards snowy environments (with a greater tread depth) should ensure that this BMW is able to serve its role throughout the year.
• A Volkswagen GTI that spends much of the year on North Carolina backroads. A summer tire will likely be the targeted market for this buyer, ensuring an enjoyable driving experience on every outing while also serving as a tire that can be driven daily. A smaller sidewall will be targeted, to ensure maximum rigidity of the tire through heavy load. A lower treadwear rating will be selected, to ensure that the tire grips properly once heated to operating temperature. A higher speed rating may even be optioned, just to be certain that the limits of the tires will never hinder the experience of the driver. An aggressive tread pattern will be selected, yet an adequately-grooved tire will be the correct option to properly channel water from underneath the contact patch in the case of a rain storm.
• A Porsche 944 that serves solely as a weekend autocross car will be specifically targeting a competitive tire that satisfies the rules and sanctions of its operating class. These tires will likely be wider than originally optioned by the manufacturer to promote the largest contact patch attainable. The sidewall width will be significantly smaller; this will allow them to clear the fenders despite the lowered ride height and hinder them from flexing and losing the contact patch under heavy load. A very low treadwear rating will be optioned, as the aim of these tires is to warm up as quickly as possible across a timed run, the soft compound stretching and grabbing the ground as the mass of the vehicle is slung around bends.
  
  Fuel economy and comfort will not be considered, as this tire selection is made with the goal of competing to the highest ability of the vehicle. The tread will likely be void of the grooves on typical street tires, optioning instead for a wide and chunky tread pattern to make as much contact with the tarmac as possible. These competitive tires will be lucky to last more than a season or two, but will be sure to translate as much performance as the vehicle has to offer.

For any vehicle and its aim of operation, there is a proper tire choice to achieve that goal. In an intimidating marketplace, the best tactic a you can utilize to ensure the proper fit to your taste is to gain an education in the elements necessary to make the decision. By taking all of the attributes listed above in this guide into account, you can guarantee a fitting choice for your vehicle, and years (or seasons) of good experiences to come.

If you have any questions about what tires to run, or what tires we prefer on our own personal vehicles, leave them in the comments section below.