How to Read & Determine Tire Size for Your Vehicle

Understanding the numbers and letters on the sidewall of your car tire is essential for making informed decisions about tire replacement or upgrades. These markings provide critical details about the tire’s size, type, and performance. Here’s a detailed breakdown:

1. Tire Type

The first letter on a tire indicates its type. For example:

P: Stands for “P-Metric,” indicating the tire is designed for passenger vehicles.
LT: Stands for “Light Truck,” which refers to tires built for vehicles carrying heavier loads.

2. Tire Width

The first three digits represent the width of the tire in millimeters. This is measured from one sidewall to the other.

Example: In a tire labeled 205/55R16, the width is 205 millimeters.

3. Aspect Ratio

This two-digit number follows the slash mark and is the ratio of the tire’s height to its width.

Example: If the aspect ratio is 55, the tire’s height is 55% of its width.

4. Construction Type

The letter R signifies a radial construction, where the layers run radially across the tire. This is the most common type of tire construction today.

5. Wheel Diameter

This is the size of the wheel (in inches) that the tire is designed to fit.

Example: In 205/55R16, the wheel diameter is 16 inches.

6. Load Index

The load index indicates the maximum weight a tire can support when properly inflated. This value can be cross-referenced in a load index chart for exact weight capacity.

7. Speed Rating

This single letter denotes the tire’s maximum speed capability. The ratings correspond to specific speed limits:

Example: A tire with a V speed rating can sustain speeds of up to 240 km/h (149 mph).

8. DOT Symbol

The letters DOT confirm that the tire meets all Department of Transportation safety standards. This marking is followed by a series of numbers indicating the tire’s manufacturing date and location.

Why Understanding Tire Markings Matters

Knowing how to read tire markings helps you:

Select the correct replacement tires for your vehicle.
Ensure optimal performance and safety.
Avoid issues related to incorrect tire size or load capacity.

If you’re looking to replace your tires, consult our tire services page or check out our guide to choosing the right tires. For detailed advice on maintaining your tires, refer to our tire care blog.

By understanding these details, you can maintain your vehicle’s performance, ensure safety on the road, and make cost-effective choices. Visit Automotive Doctor Motor Garage for expert tire services and advice.