Tire Size Calculator

Figure out your tire dimensions, compare different sizes, and see how they affect your speedometer. Because changing tire sizes isn't just about looks—it impacts your safety and how your car performs.

Enter Your Tire Size

Format: Width/Aspect Ratio/Rim Diameter

For speedometer accuracy comparison

Tire Dimensions & Analysis

Ready to Calculate Tire Dimensions?

Enter a tire size above (like 225/50R16) and see exactly what those numbers mean.

How to Read Tire Size Codes (It's Not as Complicated as It Looks)

That string of numbers on your tire sidewall actually tells you everything about the tire's size and capabilities. Let's break down what 225/50R16 means:

225

Tire width in millimeters. This tire is 225mm wide from sidewall to sidewall.

50

Aspect ratio (height to width). Sidewall height is 50% of the width. Higher numbers = taller sidewalls.

16

Rim diameter in inches. This tire fits on a 16-inch wheel.

The "R" just means it's a radial tire (vs. bias ply). Pretty much all modern tires are radial.

Why Tire Size Affects Your Speedometer (And Why It Matters)

The Math Behind It

Your speedometer works by counting how fast your tires are rotating. Larger diameter tires rotate slower at the same speed, so your speedometer thinks you're going slower than you actually are.

Example: Going from 225/50R16 (25.9" diameter) to 245/45R17 (26.7" diameter) makes your speedometer read about 3% slow. At highway speeds, that's significant.

Why This Is a Big Deal

Speedometers are calibrated for your original tire size. Changing tire sizes throws this off, and you could be driving faster than you think—especially dangerous in speed-limited areas.

Safety first: If the diameter changes by more than 3%, get your speedometer recalibrated or consider a different tire size.

Common Tire Size Changes and What They Mean

Plus-One Sizing (Same Overall Diameter)

Going from 225/50R16 to 235/50R16. Width increases but height stays the same. Minimal speedometer impact, but check clearance.

Plus-Size Wheels (Lower Profile)

Going from 225/50R16 to 225/45R17. Looks cool but reduces sidewall height. Stiffer ride, potentially more road noise.

Oversized Tires (Larger Diameter)

Going from 225/50R16 to 245/50R16. More ground clearance, better traction, but speedometer reads slow and may rub.

Pro Tip

Always check your vehicle's owner manual for acceptable tire sizes. What's "cool" might not be safe or legal for your specific car.

Tire Size Questions People Actually Ask

Can I put bigger tires on my car?

Maybe, but it depends. Check your owner manual first. Larger tires can improve ground clearance and look better, but they might rub against fenders, affect handling, and definitely impact your speedometer and fuel economy.

Do larger tires hurt gas mileage?

Yes, generally. Larger, heavier tires create more rolling resistance. Plus, if they're taller, your engine has to work harder to turn them. You might see 1-3 MPG decrease with significantly larger tires.

What's the difference between 225/50R16 and 225/50R17?

The rim size. 225/50R16 fits 16-inch wheels, 225/50R17 fits 17-inch wheels. The overall tire diameter will be slightly larger with the 17-inch rim (about 0.6 inches), so your speedometer will read a tiny bit slow.

Do I need to recalibrate my speedometer for new tires?

If the diameter changes by more than 2-3%, yes. Some modern cars can be reprogrammed, others need a physical speedometer recalibration. Check with your dealer or a tire shop.