Understanding Tire Sizes: Your Complete Guide to Tire Size Comparison

Introduction

Choosing the right tire size for your vehicle is crucial for safety, performance, and fuel efficiency. Whether you're upgrading your wheels, replacing worn tires, or exploring plus-sizing options, understanding tire dimensions is essential. Our Tire Size Calculator makes it easy to compare different tire sizes and understand how changes will affect your vehicle.

Table of Contents

1. How to Read a Tire Size Code
2. What Each Measurement Means
3. Using the Tire Size Calculator
4. Speedometer Accuracy
5. Plus Sizing Guide
6. Frequently Asked Questions

How to Read a Tire Size Code

Tire sizes are displayed in a standardized format like 225/45R17. Let's break down each component:

• 225: Section width in millimeters (the tire's width from sidewall to sidewall)
• 45: Aspect ratio (the sidewall height as a percentage of the width)
• R: Construction type (R = Radial, which is most common)
• 17: Wheel diameter in inches

What Each Measurement Means

Section Width

The section width is the tire's width in millimeters when measured at its widest point. A 225mm tire is approximately 8.9 inches wide. Wider tires generally provide better grip but may increase fuel consumption.

Aspect Ratio

The aspect ratio is the sidewall height expressed as a percentage of the section width. For a 225/45 tire, the sidewall height is 45% of 225mm = 101.25mm. Lower aspect ratios mean shorter sidewalls and often sportier handling.

Overall Diameter

The overall diameter combines the wheel size with the tire's sidewalls. This is calculated as:

Overall Diameter = Wheel Diameter + (2 × Sidewall Height)

Using the Tire Size Calculator

Our calculator makes comparing tire sizes simple:

1. Enter your original tire size (Tire 1) - the tires currently on your vehicle
2. Enter the new tire size (Tire 2) - the tires you're considering
3. Click Compare to see detailed differences

The calculator shows:

• Visual size comparison
• Exact dimensional differences
• Speedometer impact
• Revolutions per mile

Speedometer Accuracy

Changing tire sizes affects your speedometer reading because the car's computer calculates speed based on wheel rotations.

• Larger tires: Your actual speed will be HIGHER than the speedometer shows
• Smaller tires: Your actual speed will be LOWER than the speedometer shows

Most manufacturers recommend staying within ±3% of the original tire diameter to maintain speedometer accuracy and avoid voiding warranties.

Plus Sizing Guide

Plus sizing means increasing wheel diameter while adjusting tire size to maintain similar overall diameter:

Benefits of plus sizing:

• Improved handling and cornering
• Better road feel
• Enhanced appearance

Considerations:

• Ride may be firmer
• More susceptible to pothole damage
• Often higher cost

Frequently Asked Questions

Can I use a different tire size than what's recommended?

Yes, but stay within 3% of the original overall diameter. Significant changes can affect speedometer accuracy, ABS performance, traction control, and may void your warranty.

What's the best tire size for fuel economy?

Narrower tires with higher aspect ratios typically offer better fuel economy due to lower rolling resistance. However, the difference is usually minimal.

How do I know if a tire will fit my wheel?

The tire's wheel diameter (the last number in the size code) must match your wheel size. For example, a 225/45R17 tire only fits 17-inch wheels.

Will larger tires affect my odometer?

Yes, larger tires will cause your odometer to under-report actual miles driven, while smaller tires will over-report.

What does the "R" in the tire size mean?

The "R" stands for radial construction, which is the most common type of tire construction today. Nearly all passenger car tires are radial.

Disclaimer: This calculator is for informational purposes only. Always consult your vehicle manufacturer's recommendations and a professional tire specialist before making tire changes.