Understanding Tire Size Requirements

A Comprehensive Guide on Speed Rating and Load Index


Selecting the right tire size for your vehicle is crucial for optimal performance, safety, and fuel efficiency. Tire size requirements consist of several components, including the speed rating and load index. This tutorial will guide you through understanding these factors and help you make an informed decision when choosing tires for your vehicle.

1. Decoding Tire Size Information

Tire size information is typically found on the sidewall of a tire and consists of a series of numbers and letters. A common example is "P215/65R15 95H". Here's a breakdown of what each part represents:

- "P": Indicates the tire is designed for a passenger vehicle.

- "215": Represents the tire's width in millimeters.

- "65": Represents the aspect ratio, which is the height of the tire sidewall as a percentage of the tire's width.

- "R": Indicates that the tire is a radial tire.

- "15": Represents the diameter of the wheel in inches.

- "95": Represents the load index, which indicates the maximum load capacity of the tire.

- "H": Indicates the speed rating, which represents the maximum speed at which the tire can safely operate.

2. Understanding Load Index

The load index is a numerical code that corresponds to the maximum weight a tire can support when properly inflated. To find the load capacity of a tire, you can refer to a load index chart. Here are a few examples:

- Load Index 91: 1,356 lbs (615 kg) per tire

- Load Index 95: 1,521 lbs (690 kg) per tire

- Load Index 100: 1,764 lbs (800 kg) per tire

Always choose a tire with a load index equal to or greater than the original equipment tires on your vehicle to ensure optimal safety and performance.

3. Understanding Speed Rating

The speed rating is represented by a letter and indicates the maximum speed at which a tire can carry a load corresponding to its load index. The higher the speed rating, the better the tire's high-speed performance and handling. Here are some common speed ratings:

- S: Up to 112 mph (180 km/h)

- T: Up to 118 mph (190 km/h)

- H: Up to 130 mph (210 km/h)

- V: Up to 149 mph (240 km/h)

- W: Up to 168 mph (270 km/h)

It is crucial to select a tire with a speed rating appropriate for your vehicle's top speed and performance requirements.

4. Selecting the Right Tire Size, Speed Rating, and Load Index

When choosing tires for your vehicle, follow these steps:

a) Check your vehicle's owner's manual or the placard on the driver's door jamb for the manufacturer's recommended tire size, load index, and speed rating.

b) Ensure the tire size matches the dimensions of your wheels, as well as your vehicle's clearance and suspension requirements.

c) Choose a load index that meets or exceeds the recommended value to ensure your tires can safely support your vehicle's weight.

d) Select a speed rating appropriate for your vehicle's performance and the driving conditions you typically encounter.


Understanding tire size requirements, including speed rating and load index, is essential for selecting the right tires for your vehicle. By following this tutorial and referring to your vehicle's owner's manual, you can make an informed decision and ensure optimal safety, performance, and fuel efficiency. Always consult a professional if you have any doubts or concerns about tire selection.