A simple guide to understanding your car's tire size
2 Minute Read
Have you ever stared at the side of your tire and wondered what all those numbers and letters mean?
Choosing the correct tire size is more than just a technical detail—it's essential for your car's safety, performance, and fuel efficiency. Whether you're replacing worn-out tires or upgrading for better handling, you'll need to understand where to find the size and how to decode those letters and numbers to shop confidently.
Picking the wrong size can lead to poor handling, reduced fuel efficiency, and even inaccurate speedometer readings. But don't worry. If you have questions, CAA's Mobile Tire Sales is happy to help and offer competitive prices for at-home installation.
Where can you find your tire size?
You can typically find it in one of these four places on your vehicle or its documentation:
Tire's sidewall: This is the most common and visible place to find your tire size.
Driver's side door jamb: Open the driver's door and check the inner frame. Many vehicles have a label listing the manufacturer-recommended tire specifications.
Inside your glove box door: Some vehicles include information here as a backup.
Your vehicle owner's manual: Size details are also in the manual, often under the specifications or tires and wheels section.
Decoding your tire size
Your vehicle's tire size information looks like P225/65R17 95T. Here's what each part signifies:
Tire type (P)
The first letter indicates the type of vehicle the tire is for:
-
P: Passenger vehicles, including cars, SUVs, minivans, and light pickup trucks.
-
LT: Light trucks designed for carrying heavy payloads or towing.
-
T: Temporary or spare tires.
-
ST: Special trailer tires are meant for trailers only.
Tire width (225)
The three-digit number after the type is the width from sidewall to sidewall in millimetres. For example, 225 means the tire is 225 millimetres wide.
Aspect ratio (65)
The aspect ratio represents the height of the sidewall as a percentage of the tire's width. If the aspect ratio is 65, the tire's height is 65 per cent of its width.
Construction (R)
The second letter explains how it was made.
-
R: Radial, which is the standard for most modern tires, where the layers of fabric run radially across the tire.
-
B or D: Bias-ply, an older construction method with layers that run diagonally, is still used for specialty tires, such as off-road vehicles, due to their robust sidewall structure.
Rim diameter (17)
The third number indicates the wheel size (rim) that the tire fits. A 17 means the tire will fit a 17-inch wheel.
Load index (95)
The load index, which is the fourth number, shows the maximum weight a tire can carry when properly inflated. For example, a load index of 95 means each tire can support up to 690 kg.
Speed rating (T)
The speed rating indicates the maximum speed your tire can handle safely. For instance:
-
S: Up to 180 km/h
-
T: Up to 190 km/h
- H: Up to 210 km/h
Choosing a tire with the correct speed rating is crucial for safety and performance.
All-weather or winter tires
Additional markings such as M+S (mud and snow) or the mountain and snowflake symbol indicate a tire's suitability for winter or all-weather conditions.
Need new tires? CAA can help!
You don't have to do it alone when it comes to finding and purchasing the right tires. CAA's Mobile Tire Sales brings the process right to your doorstep, and we can also store your tires.
To begin, enter your vehicle's tire size to browse the options. Once your purchase is complete, you will receive a confirmation email with a link to schedule your at-home tire installation.
Not a Member yet? Join today to utilize our Pit Crew services and other exclusive benefits.
