How to Read Tire Size: A Simple Guide for Everyday Drivers

Epic Tech Tips
Oct 27
3 min read

Reading tire size helps you pick the right tires for safe and smooth driving. Those numbers and letters on the sidewall give important details.

Once you learn what each part of the code means, choosing the correct tire becomes simple. You’ll understand width, height, and rim size quickly.

With a little guidance, anyone can decode tire markings and make smart choices when it’s time to replace tires.

TL;DR

Tire size is shown on the sidewall in a code like P215/70R15, where P tells the tire type (Passenger), 215 is the width in millimeters, 70 is the aspect ratio showing that the sidewall height is 70% of the width, R means radial construction, and 15 is the rim diameter in inches; understanding this, plus the load index and speed rating, helps drivers choose the right tire for safe and smooth performance.

What Tire Size Looks Like

Most tires show a code like P215/70R15 or 225/65R17. Each part tells a different story about the tire.

Breakdown of P215/70R15:

P: Type of tire
215: Tire width in millimeters
70: Aspect ratio (sidewall height as a percent of width)
R: Radial construction
15: Rim diameter in inches

Short and simple: The numbers show width, height, and wheel size. The letters show type and build.

Also read: What Size Windshield Wipers Do I Need

Tire Type: What the First Letter Means

A tire may start with a letter. It shows what kind of vehicle the tire is made for.

Common letters include:

P = Passenger vehicle
LT = Light truck
T = Temporary tire (like a spare)
C = Commercial tire

If there is no letter, the tire often follows European sizing standards.

Knowing tire type matters for safety and performance.

Tire Width: First Three Numbers

The first group of three numbers shows tire width in millimeters.

Example: 225/65R17

Here, 225 means the tire is 225 mm wide.

Wider tires give more grip, but they can also use more fuel. Drivers should follow the size recommended by the vehicle maker.

Aspect Ratio: The Height of the Sidewall

The number after the slash ( / ) is the aspect ratio.

It is a percentage of the width.

Example: 225/65R17

Width: 225 mm
Aspect Ratio: 65
Sidewall height = 65% of 225 mm
That equals 146.25 mm

A smaller aspect ratio means a shorter sidewall.

Shorter sidewalls often improve handling but may feel less smooth.

Also read: What Is the Width of a Standard King Size Bed

Construction Type: Letter in the Middle

The R stands for Radial, which means the layers inside the tire run across the tire.

Most modern tires are radial because they:

Improve stability
Last longer
Handle heat better

If someone sees D or B, that refers to older types of construction, not common today.

Rim Diameter: Last Two Numbers

The final number shows the wheel size in inches.

Example: R17

Fits a 17-inch rim

Rim size must match exactly. A tire for a 17-inch rim cannot fit a 16- or 18-inch rim.

A Real Example Explained

When someone asks, “What does 225/65R17 mean?”

It tells them:

225 mm wide
Sidewall height is 65% of the width (146.25 mm)
Radial tire
Fits 17-inch wheels

This quick breakdown helps you understand any tire you see.

Extra Sidewall Markings That Matter

Besides the main size code, a tire also includes:

Load Index

A number like 91
Shows how much weight a tire can safely carry

Speed Rating

A letter like T
Shows the maximum safe speed

Other Marks

C: Commercial
M+S: Mud and Snow
3PMSF: Better winter traction (Three-Peak Mountain Snowflake)

These markings help match tires to driving needs.

Quick Tire Size Table

Here is a short reference for what each part means:

Marking	What It Tells	Example
P	Tire type	P = Passenger
215	Tire width	215mm wide
70	Aspect ratio	70% of width
R	Construction	Radial
15	Wheel diameter	Fits 15-inch wheel
91	Load index	Weight limit
T	Speed rating	Max safe speed

A Simple Step-By-Step Checklist (One List)

When reading a tire size, they can follow this:

Identify the tire type (P, LT, or none)
Look at width in millimeters
Check aspect ratio for height difference
Confirm radial construction (R)
Match wheel diameter exactly
Review load index and speed rating

Final Takeaway

Every driver should know how to read tire size. It helps them make smart choices when replacing tires and keeps their vehicle performing at its best. The code may look tricky at first, but after reading this guide, anyone can decode it with confidence.

Right tire size = better safety, better comfort, and better control.

If another tire size seems unclear, they can just look at the sidewall again — because now they know exactly what it means.