Many car owners tend to overlook the various markings present on the sides of their tires, thinking that identifying the brand and model of their tires will suffice when it comes to replacing them. However, in addition to the brand and model information, there are markings that indicate the tire’s size and compliance with safety standards set by the federal government. These markings serve as proof that the tire meets safety regulations and size requirements.
Furthermore, the Uniform Tire Quality Grading code can be found on the tire, providing essential information on the maximum amount of inflation pressure, load, and speed that the tire can handle. Being aware of these markings and their meanings can help car owners make informed decisions when purchasing or replacing tires, ensuring optimal safety and performance on the road.
How to Read Tire Number and Size?
Typically, when an individual needs to buy a new tire, they rely on a tire shop or dealership to determine the appropriate size for the replacement tire. However, by understanding the markings on the sides of the tires, one can save a considerable amount of money and obtain the desired tires themselves. It is also important to consider the space saver tire stored in the trunk. To read tire size properly, we have compiled 5 essential points every car owner should know before purchasing a tire.
1. Tire Type
It is crucial to ensure that the tire you choose is the appropriate type before considering the specific size measurements. Different types of vehicles require different tire types, such as those designed for passenger cars or light trucks.
To determine the tire type, examine the side wall of the tire and look for a series of numbers starting with one or two letters. If the numbers start with a “P,” it indicates that the tire is intended for passenger cars. On the other hand, if it starts with “LT,” it is meant for light trucks.
Temporary spares, also known as donut spares, have similar markings but are designated with a “T” before the tire size. It is essential to ensure that the tire type and size match the specifications recommended by the vehicle manufacturer to ensure safety and optimal performance on the road.
2. Tire Width
The width of the tire can be expressed in either millimeters or inches, depending on the manufacturer. If the tire size information consists of three numbers following the letter mentioned earlier, it represents the tire’s width in millimeters. On the other hand, if only two numbers are present after the letter, the width is expressed in inches.
The width measurement refers to the distance between the two sides of the tire, measured in a straight line. By understanding how to interpret the width measurements, one can select a tire that meets the vehicle’s recommended specifications, ensuring optimal safety and performance.
3. Aspect Ratio
Following the tire width measurement, there will be a forward slash, followed by a number representing the tire’s aspect ratio. This ratio is a measurement of the height of the tire’s sidewall in relation to the width.
The aspect ratio is expressed as a percentage of the tire’s width, with the number indicating the percentage of the width that equals the height of the tire’s sidewall. For example, if the aspect ratio is 60, then the tire’s height is 60% of its width.
A higher aspect ratio means that the tire’s sidewall is taller or higher, while a lower aspect ratio indicates a shorter or lower sidewall. “Low profile” tires, which are commonly seen on sporty cars, have a lower aspect ratio and appear thinner from the side. Understanding the aspect ratio can help individuals choose a tire that meets their specific needs and preferences.
4. Tire Construction
After the aspect ratio number, there may be a letter that indicates the type of tire construction. The most common letter found in this position is “R,” which stands for radial construction. Radial tires are the most widely used tire construction technique today.
Less commonly, you may encounter other letters, such as “B” for belted bias or “D” for diagonal bias. These construction techniques are used less frequently than radial construction, but a professional auto mechanic will be familiar with them and understand what they mean. Understanding the type of tire construction can be helpful when selecting a tire that is best suited for your specific vehicle and driving needs.
5. Wheel Diameter
The next number listed on the tire’s sidewall represents the wheel diameter size. Typically listed in inches, this number indicates the size of the wheel that can be mounted on the tire. For example, if the number following the “R” is 18, then the tire is compatible with a wheel that has an 18-inch diameter.
6. Load Index
Following the wheel diameter size, you’ll find the load index, which is a numerical value indicating the maximum weight that the tire can safely carry. The load index is typically represented by a two- or three-digit number that corresponds to a specific weight capacity, with values ranging from 75 (which can support a weight of up to 853 lbs.) to 125 (which can support a weight of up to 3,638 lbs.), although some tires may have a lower or higher load index.
To determine the maximum weight that a specific load index can support, you can refer to a Load Index chart, which provides the corresponding weight capacity for each index value. It’s important to choose a tire with a load index that meets or exceeds the weight requirements of your vehicle to ensure optimal safety and performance.
Load Index Chart
Here is the load index char of tires:
The final component of the tire size code is the speed rating, which is indicated by a letter and denotes the maximum speed at which the tire can handle the weight associated with its load index. Speed ratings are typically designated by a letter ranging from L (75 mph) to Y (186 mph), with Z used for tires rated above 149 mph.
It’s vital to select a tire with a speed rating that meets or exceeds the speed capabilities of your vehicle, as specified by the manufacturer. It’s always advisable to refer to your vehicle’s owner’s manual or consult the tire manufacturer for guidance on the recommended tire size, load index, and speed rating.
The majority of tires are sized using the metric tire notation, which gives you detailed information about tire width, aspect ratio, wheel diameter, load index, and speed rating. For example, a tire labeled P205/60R17 82S can be deciphered as follows:
- The letter “P” preceding the tire width signifies that it is a tire designed for passenger cars.
- The first number “205” indicates the tire’s width in millimeters, which is approximately 8.1 inches.
- The aspect ratio, represented by the number “60,” is the percentage of the tire’s height to its width, indicating that the tire’s height is 60% of its width.
- The letter “R” denotes the tire’s construction type, indicating that it is a radial tire, which is the most commonly used construction type.
- The number “17” indicates the wheel diameter in inches, indicating that the tire is suitable for a 17-inch wheel.
- The load index, represented by the number “82,” denotes the tire’s maximum load-carrying capacity, with this tire being able to carry up to 1,047 pounds according to the load index chart.
- Finally, the speed rating is represented by the letter “S,” indicating that the tire has a maximum speed rating of 112 MPH, as per the speed rating chart.
Importance of Proper Tire Pressure
Regularly checking the tire pressure of your vehicle is crucial to ensure optimal safety, fuel efficiency, and braking distance. It is recommended to perform this task at least once a month, when the tires are cold (not immediately after driving), and especially before embarking on a long trip.
To determine the recommended tire pressure for your specific car, refer to the Tire and Loading Information Label, which can typically be found on the driver’s side door edge or post. You can also consult your car owner’s manual. It’s important to note that the correct tire pressure is based on the vehicle manufacturer’s recommendation, not the numbers imprinted on the tire itself.
Custom Tire Upgrades
If you are considering upgrading your vehicle’s wheels and tires, it is crucial to select the appropriate size. When upgrading, keep the following factors in mind:
- Width: While a wider tire can enhance traction, it is vital to ensure that the new tire’s width fits your vehicle’s rims and wheel wells without causing any rubbing problems. Keep in mind, wider tires reduce mileage considerably.
- Diameter: If you opt to increase your tire’s diameter, you may also need to get a larger rim size. This upgrade can enhance your vehicle’s stability, but it is worth noting that larger tire and wheel combinations add weight and may affect your ride quality.
- Sidewall: A lower aspect ratio will result in a shorter tire sidewall, which can improve handling and responsiveness. However, be aware that this may also result in a rougher ride quality.