What do tire size numbers mean?

A tire size like 225/45R17 means: 225 is the width in millimeters, 45 is the aspect ratio (sidewall height as a percentage of width), R means radial construction, and 17 is the rim diameter in inches. Use our calculator above to see all dimensions.

How much bigger can I go on tire size?

Most experts recommend staying within 3% of your original tire's overall diameter. This ensures your speedometer stays accurate and vehicle systems function properly. Our calculator shows the exact percentage difference when comparing two sizes.

Does tire size affect speedometer accuracy?

Yes. A larger tire covers more ground per revolution, making your speedometer read slower than actual speed. A smaller tire does the opposite. For example, if you switch from a 25-inch to a 26-inch overall diameter tire, at a speedometer reading of 60 mph you would actually be going about 62.4 mph.

What is the most common tire size?

The most popular tire sizes in the US are 225/45R17, 205/55R16, and 215/55R17. These fit a wide range of sedans and small SUVs. Truck and SUV owners commonly use 265/70R17 and 275/55R20.

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Enter your tire size to instantly calculate dimensions, or compare two sizes side by side to see the exact differences in diameter, circumference, and speedometer accuracy.

Width (mm)

Aspect Ratio (%)

Rim Diameter (in)

Tire 1 — Width

Aspect

Rim

Tire 2 — Width

Aspect

Rim

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DimensionTire 1Tire 2Diff

Speedometer Impact

Popular Tire Sizes

Understanding Tire Sizes

📏 Width (225)

The first number is the tire's section width in millimeters, measured from sidewall to sidewall. A 225 tire is 225mm (8.86 inches) wide.

📐 Aspect Ratio (45)

The sidewall height as a percentage of the width. A 225/45 tire has a sidewall of 225 × 0.45 = 101.25mm. Lower numbers = sportier, stiffer ride.

🔄 Construction (R)

R = Radial (most modern tires). D = Diagonal/Bias-ply (older, specialty). B = Belted. Radial tires offer better handling and fuel economy.

⭕ Rim Diameter (17)

The wheel rim diameter in inches. This must match your wheel size exactly. Common sizes range from 14" (economy cars) to 22" (trucks, luxury SUVs).

Frequently Asked Questions

A tire size like 225/45R17 means: 225 is the width in millimeters, 45 is the aspect ratio (sidewall height as a percentage of the width), R means radial construction, and 17 is the rim diameter in inches. Use our calculator above to see all the dimensions for any tire size.

Yes, but within limits. The general rule is to keep the overall diameter within 3% of the original size. Going too far outside this range can affect speedometer accuracy, ABS, traction control, and may void your warranty. Use our comparison tool above to check the exact difference before buying.

Most experts recommend staying within 3% of your original tire's overall diameter. This ensures your speedometer stays accurate and vehicle safety systems function properly. You also need to ensure the wider or taller tire doesn't rub against your wheel wells or suspension components.

Yes! A larger tire covers more ground per revolution, making your speedometer read slower than your actual speed. A smaller tire does the opposite. Our comparison calculator shows you the exact speedometer impact when switching sizes.

The most popular sizes in the US are 225/45R17, 205/55R16, and 215/55R17 — fitting a wide range of sedans and small SUVs. For trucks and larger SUVs, 265/70R17 and 275/55R20 are very common.