How to Read Tire Size

Tire sizing can be confusing, but once you understand the code, it's actually quite simple. Every tire has a size code like "265/70R17" printed on the sidewall. Let's break it down:

The Tire Size Code Breakdown

Width (265)

The first number represents the tire's width in millimeters from sidewall to sidewall. So a 265mm tire is quite wide.

Aspect Ratio (70)

This is the ratio of the tire's height to its width. A 70 means the height is 70% of the width. So for our 265mm wide tire, the height would be 185.5mm.

Construction (R)

This letter indicates the tire's construction type. "R" means radial construction, which is the most common type today.

Rim Diameter (17)

The final number is the diameter of the wheel in inches that this tire is designed to fit.

Real-World Examples

Let's look at some common tire sizes:

• 225/45R17 - Compact car tire, narrower and lower profile
• 275/40R20 - Performance tire, wider and taller
• 31x10.5R15 - Off-road tire using inches instead of millimeters

Why Tire Size Matters

Choosing the right tire size affects:

• Vehicle handling - Too wide tires can rub against fenders
• Fuel efficiency - Larger tires create more rolling resistance
• Speedometer accuracy - Different sizes can affect your speed reading
• Ground clearance - Larger tires increase ride height

Checking Your Current Size

You can find your tire size in several places:

1. Tire sidewall - Look for the size code
2. Driver's door jamb - Sticker with recommended sizes
3. Owner's manual - Original equipment specifications
4. Current tires - All four should be the same size

Tire Size Calculator

When changing tire sizes, use this formula to understand the impact:

New Tire Diameter = Rim Diameter + (2 × Tire Height)

This helps ensure your new tires won't cause clearance issues or speedometer errors.