Tire size can be confusing. Some numbers on the sidewall are listed in millimeters while others are inches. Plus, the right size for your car, truck, or trailer can differ depending on where and how you drive. This is the sizing recommended by the vehicle manufacturer. Next, have a tire professional help you determine a tire size range that will fit your vehicle and driving needs.
P stands for passenger vehicle tire. P-class tires include cars, SUVs, crossovers, minivans and smaller pickup trucks. LT means light truck tire , designed for vehicles that are capable of carrying heavy loads, towing trailers, or for those looking for an extra heavy duty option. These are often equipped on three-quarter or 1 ton trucks and SUVs. However, the number does correspond to a specific load capacity listed in an index.
Beginning with 1 and ending with , numbers in the load index represent carrying capacities of 99 to lbs. There are two types of load types for passenger tires though, Standard Load and Extra Load.
If a tire is Standard Load there will be no markings indicating it but if it is Extra Load the letters XL will appear after the size and load index. The first number is the load index if the tire is used in a single application, the second number is the load index if the tire is used in a dual application. Passenger type tires cannot be used in a dual application.
Load Range is an older term that is still commonly used in the industry so you may hear your tire dealer reference it but the load index numbers are the best way to ensure you have the proper tire. One important but often misunderstood facet about load index is that the load index numbers between standards organizations P-Metric vs Euro-Metric are not necessarily on the same scale. Meaning that two tires in the two different systems that have the same load index number could have different maximum load capacities.
Just as your load index number corresponds to a specific load, your speed rating letter corresponds to a particular speed capability based on a standardized laboratory test. Of course, you should always follow legal speed limits on roadways. There is one last sizing type that you should know about, especially if you are in the market for off road tires for a light truck or SUV.
Flotation sized tires are similar to LT-Metric tires in application except for a few important points. Number one, they cannot be used in dual applications and number two, an equivalent size tire may have different load capacity than its LT-Metric counterpart. The first number in the Flotation tire size is the overall diameter in inches.
Tire Width Is the width of the tire measured in millimeters from sidewall to sidewall. The first three-digit number in the tire size refers to the tire width. Aspect Ratio Is the ratio of the height of the tire's cross-section to its width. The two-digit number after the slash mark in a tire size is the aspect ratio.
The bigger the aspect ratio, the bigger the tire's sidewall will be. Construction The letter "R" in a tire size stands for Radial, which means the layers run radially across the tire. Wheel Diameter Is the size of the wheel measured from one end to the other. It tells us the size of the wheel that the tire is intended to fit.
Load Index Indicates the maximum load that the tire can support when properly inflated. You'll also find the maximum load on the tire sidewall, in both pounds and kilograms.
Learn more about tire load index. Speed Rating Tells you the maximum speed capability of a tire. Often speed ratings are matched to the top speed capability of the vehicle. Goodyear does NOT recommend exceeding legally posted speed limits. Learn more about tire speed rating. Temperature Grades Speeds in mph A Over B Between and C Between 85 and Treadwear grades are based on standardized government tests to help predict the expected treadwear of a tire.
Learn More. Tire Maintenance. How to Put Air in Tires. Tread Depth. This tire is already added to your appointment. Go To Appointment. You can only add one product to your appointment. Physically, they have about the same dimensions and appear to fit interchangeably, but you will notice a difference in the two- or three-digit number following the size called the load index.
The higher the load index, the greater the load-carrying capacity of the tire. Why the difference? Both types use different load and inflation formulas; as a result, a metric tire has a slightly greater load index and higher load-carrying capacity reserve than its P-metric counterpart. Learn how to decode tire size and other data. Hence, if your car came with P-metric tires, you can replace them with P-metric or Metric tires.
The Metric tire will have greater load capacity reserve than what came on the car as original equipment and is an acceptable substitute. A number of tire manufacturers allow for this substitution. This is true within certain limitations, but the conversion is best left to the professional tire dealer who has access to a tire fitment guide for proper tire replacement.
Overall, the best practice is to replace tires with the same size designation and load index that originally came on your car.
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