Most drivers only think about their tires when one goes flat or a mechanic points out they are worn. Yet, those four patches of rubber are the only parts of your vehicle that touch the road. Understanding what they do and how to choose the right ones is fundamental to your car’s safety and performance. The string of characters on a tire’s sidewall might look like a secret code, but it contains everything you need to know.
Decoding the Numbers and Letters on Your Tire’s Sidewall
At first glance, the sidewall of a tire is a confusing jumble of letters and numbers. It feels like information meant only for technicians. However, learning how to read tire size is surprisingly straightforward once you break it down. Let’s use a common example, P215/55R17 97V, and go through it piece by piece to understand what these tire numbers mean.
Tire Service Type: The First Clue
The sequence often begins with a letter like ‘P’, which stands for P-Metric. This indicates the tire is designed for passenger vehicles, including cars, minivans, and smaller SUVs. If you see ‘LT’, it means Light Truck. These tires are built with reinforced construction to handle the heavier loads associated with vehicles used for hauling and towing, a common requirement for many of the trucks we cover. Another less common type is ‘ST’ for Special Trailer, designed exclusively for trailer axles.
Core Size Metrics: Width, Aspect Ratio, and Construction
Following the service type, the first number, 215, represents the tire’s width from one sidewall to the other in millimeters. The next number, 55, is the aspect ratio. This means the sidewall’s height is 55% of the tire’s width. A lower aspect ratio results in a shorter, stiffer sidewall, which generally improves handling but can make the ride feel firmer. The letter ‘R‘ signifies that the tire has a Radial construction, the modern standard for nearly all cars on the road in the United States. Finally, the number 17 indicates the tire is made to fit a 17-inch diameter wheel.
Load Index and Speed Rating: The Safety Codes
The last part of the code, 97V, relates directly to safety. The ‘97‘ is the tire’s load index, a code that corresponds to the maximum weight it can safely support when properly inflated. The ‘V‘ is the speed rating, indicating the maximum speed the tire can sustain. It is absolutely essential that the tires you choose meet or exceed the load index and speed rating specified by your vehicle’s manufacturer. These are not suggestions but critical safety minimums.
| Component | Example | What It Means |
|---|---|---|
| Service Type | P | Designed for Passenger vehicles. Other types include LT (Light Truck). |
| Section Width | 215 | The tire’s width from sidewall to sidewall in millimeters. |
| Aspect Ratio | 55 | The sidewall height is 55% of the tire’s width. |
| Construction | R | Radial construction, the standard for modern cars in the U.S. |
| Wheel Diameter | 17 | The tire is designed to fit a 17-inch diameter wheel (rim). |
| Load Index | 97 | A code for the maximum weight the tire can support (in this case, 1,609 lbs). |
| Speed Rating | V | The maximum safe speed the tire can sustain (in this case, 149 mph). |
Note: The load index and speed rating must always meet or exceed the specifications provided by your vehicle’s manufacturer for safe operation.
Locating Your Vehicle’s Official Tire Information
Now that you can decipher the code on your current tires, you might assume that’s the size you should buy. Not so fast. The tires on your car might not be the correct ones, especially if you bought the vehicle used. The definitive source for your vehicle’s tire specifications is the manufacturer, and they make this information easy to find.
Your vehicle has a tire information placard that lists the original equipment (OE) tire sizes and recommended inflation pressures. You can typically find this sticker in one of three places:
- The driver’s side door jamb
- The inside of the glove box door
- The inside of the fuel filler door
Your owner’s manual is another excellent resource, containing detailed specifications for your vehicle. For newer models with advanced features, like the systems found in the latest luxury SUVs we’ve reviewed, adhering to these specs is even more critical. Modern safety systems like anti-lock brakes (ABS), traction control, and electronic stability control are all calibrated to the original tire’s diameter. Even your speedometer’s accuracy depends on it. Using a different size can compromise the performance of these systems. Most importantly, never install a tire with a lower load index than what the manufacturer specifies. It creates a dangerous situation where the tire may fail under the vehicle’s weight.
Factors to Consider Beyond Tire Size
With the correct tire size confirmed, the process of choosing new tires for my car moves into more personal territory. The best tire is not a one-size-fits-all solution. It depends on where you live, how you drive, and what you drive. This is where you match a tire’s characteristics to your daily reality.
Matching Tires to Your Local Climate
Your local weather is a primary consideration. A driver in sunny Arizona has vastly different needs than someone navigating Minnesota winters. Tires are engineered with specific rubber compounds for different temperature ranges.
- Summer Tires: Offer maximum grip and handling in warm conditions but become hard and lose traction below 45°F.
- All-Season Tires: A compromise designed to provide acceptable performance in a wide range of conditions, including light snow. They are the default for most passenger cars.
- Winter Tires: Use soft rubber compounds and special tread designs to maintain flexibility and grip in snow and ice. They are a must-have for regions with harsh winters.
Aligning Tire Choice with Driving Habits
Think about your daily commute. Are you a highway warrior who values a quiet ride and long tread life? Or do you enjoy spirited drives on winding back roads and prioritize sharp handling and grip? Tire manufacturers offer models that cater to both ends of this spectrum. A touring tire emphasizes comfort and longevity, while a performance tire sacrifices some tread life for superior cornering ability.
Considering Vehicle Type and Load
The type of vehicle you drive also dictates your choice. An owner of a powerful truck like the 2025 Ford F-150 we recently examined who frequently tows a trailer needs ‘LT’ tires with a high load index to manage the extra weight. In contrast, a family with a Honda CR-V will likely prioritize a tire that offers a smooth, quiet ride and dependable all-season traction.
The Rise of EV-Specific Tires
Electric vehicles present a unique set of challenges. Their heavy batteries and instant torque delivery demand tires with stronger construction and more durable compounds. Additionally, since range is a top priority, EV-specific tires are designed with low rolling resistance to maximize efficiency. This is a key consideration in the growing market for the electric cars we’ve explored.
The Critical Importance of a Matched Set
When it comes to replacing tires, one rule stands above all others: use a matched set of four identical tires. It might be tempting to replace only the two most worn tires to save money, but mixing tire models, brands, or even tread depths can create unpredictable and unsafe handling. Your car is designed to perform with four identical points of contact, and any variation can lead to a loss of control during emergency braking or cornering.
For vehicles with All-Wheel Drive (AWD), this rule is non-negotiable. AWD systems are engineered to manage power distribution with extreme precision. Even small differences in tire circumference, caused by uneven wear, can force the system to work constantly to compensate. This puts significant strain on the drivetrain and can lead to expensive damage. This is especially true for modern AWD systems, like those found in a vehicle such as the Jeep Grand Cherokee, which are designed for precise power distribution. In fact, as experts at Tire Rack stress, even small differences in tread depth between tires on an AWD vehicle can strain the drivetrain.
If replacing only two tires is unavoidable, the industry best practice is to install the new pair on the rear axle. This applies whether your car is front-wheel drive, rear-wheel drive, or all-wheel drive. New tires have deeper tread and provide better grip, especially in wet conditions. Placing them on the rear helps prevent oversteer, a dangerous situation where the rear of the car loses traction and spins out. While this is a valid harm-reduction strategy, a matched set of four remains the safest choice.
Essential Maintenance for Tire Health and Longevity
Once you have invested in a new set of tires, protecting that investment requires a few simple habits. These car tire maintenance tips will not only extend the life of your tires but also improve your vehicle’s safety and fuel efficiency. Think of it as a simple monthly checklist for your car’s foundation.
Monthly Pressure Checks for Safety and Efficiency
Proper inflation is the single most important factor in tire care. Check your tire pressure at least once a month when the tires are cold. Use the recommended pressure listed on your vehicle’s door jamb placard, not the maximum pressure printed on the tire’s sidewall. An underinflated tire flexes excessively, building up heat and increasing the risk of a blowout. It also hurts fuel economy. A properly inflated tire ensures it can support its maximum weight, which is a key part of what the tire load index explained earlier is all about.
Monitoring Tread Depth for Adequate Grip
Your tire’s tread is responsible for channeling water away and maintaining grip. As it wears down, its effectiveness diminishes. The legal minimum tread depth in most states is 2/32 of an inch. You can easily check this with the “penny test.” Insert a penny into the tread with Lincoln’s head upside down. If you can see the top of his head, it is time for new tires.
Regular Rotations to Ensure Even Wear
Tires wear at different rates depending on their position on the vehicle. To ensure they wear evenly, they should be rotated regularly, typically every 5,000 to 8,000 miles. Your mechanic will follow a specific rotation pattern depending on whether your vehicle is front-wheel, rear-wheel, or all-wheel drive.
Wheel Alignment for Straight Tracking
Potholes and curbs can knock your wheels out of alignment, causing the car to pull to one side and creating rapid, uneven tire wear. If you notice your car is squeaking when you drive or pulling to one side, as we discussed in our guide to car noises, it could be a sign that your wheels need to be aligned. A proper alignment ensures all four wheels are pointed in the same direction, providing stability and maximizing tire life.