Tire Size Calculator

Calculate tire dimensions and compare sizes with visual representations

🚗 Tire Size Calculator

Calculate tire dimensions and compare sizes with visual representations

What is a Tire Size Calculator?

A tire size calculator is a powerful tool that helps you understand and compare tire dimensions based on standard tire size codes (e.g., 225/65R17). It computes overall tire diameter, sidewall height, width, circumference, and revolutions per mile, making it easy to select the right replacement or upgrade tires for your vehicle.

The calculator converts between metric and inch units for key tire dimensions, helping you visualize how a size change will affect your vehicle's speedometer accuracy, odometer readings, and overall performance. It's essential for anyone considering plus-sizing, off-road tires, or any deviation from OEM specifications.

By using this calculator, you can ensure that your new tires maintain proper fit, preserve vehicle safety systems (ABS, traction control, stability control), and avoid clearance or rubbing issues that could damage your vehicle.

How to Use the Tire Size Calculator

Enter your current tire size using the three numbers from your tire's sidewall: width (in mm), aspect ratio (%), and wheel diameter (in inches). For example, 265/70R17 means 265mm width, 70% aspect ratio, and 17-inch wheel.
If you're planning to change wheel sizes, select 'Yes' and enter your new wheel diameter. The calculator will suggest alternative tire sizes that maintain similar overall diameter.
Click 'Calculate Tire Dimensions' to see detailed specifications including section width, sidewall height, overall diameter, circumference, and revolutions per mile.
To compare two different tire sizes, switch to the 'Compare Two Tires' tab and enter both tire sizes. The calculator will show visual representations and detailed comparisons.
Review the results to ensure your new tire size stays within the recommended ±3% diameter difference to maintain speedometer accuracy and vehicle safety systems.

Latest Insights on Tire Sizing

The 3% Rule for Safe Tire Sizing

Modern recommendations commonly use the '3% rule': keep the new tire's overall diameter within about ±3% of the original to limit speedometer and odometer inaccuracy and avoid stressing drivetrain and safety systems. A tire that is 3% taller can make your actual speed about 63.3 mph when the speedometer reads 60 mph, and similarly under-reports mileage on the odometer.

Impact on Vehicle Systems

Changes in diameter and revolutions per mile affect not only indicated speed, but also shift points, fuel economy, and electronic driver aids that rely on wheel-speed data. Modern vehicles with advanced driver-assistance systems (ADAS) are particularly sensitive to tire size changes, as these systems depend on accurate wheel speed sensors for proper operation.

Understanding Tire Size Codes

Proper interpretation of size codes remains standard and is essential for making informed choices:

First number = section width in mm (e.g., 225 mm)
Second number = aspect ratio (sidewall height as % of width; e.g., 70 means height = 70% of width)
Third number = rim diameter in inches (e.g., 16)
Additional markings may include load index and speed rating, which are critical for safety

Technical Details and Formulas

Calculation Formulas

The calculator uses these standard formulas: Tire height (overall diameter) ≈ 2 × sidewall height + rim diameter. Circumference ≈ diameter × π. Revolutions per mile ≈ 63,360 ÷ circumference (in inches). These geometric relationships help you understand how tire dimensions affect vehicle performance.

Speedometer and Odometer Accuracy

When you change tire sizes, your speedometer and odometer readings can become inaccurate. A larger diameter tire covers more ground per revolution, making your actual speed higher than indicated. The calculator shows you exactly how much your speedometer will be off, helping you decide if recalibration is needed.

Clearance Considerations

While the calculator shows dimensions, physical clearance still requires expert or visual checking. Larger diameter or wider tires can rub on fenders, suspension components, or wheel wells. Always verify that your chosen tire size has adequate clearance, especially when turning or under load.

Load Index and Speed Rating

Remember that a tire size calculator does not replace checking load index and speed rating. Always ensure replacements meet or exceed the vehicle's specified ratings for these safety-critical specifications. Larger, heavier tires can also affect ride quality, acceleration, and fuel consumption.

Frequently Asked Questions

What does the aspect ratio mean in tire sizing?

The aspect ratio is the second number in a tire size (e.g., 70 in 265/70R17) and represents the sidewall height as a percentage of the tire's width. A 70 aspect ratio means the sidewall height is 70% of the tire's width. Lower aspect ratios (like 40 or 50) mean shorter sidewalls and typically sportier handling, while higher ratios (like 70 or 75) provide more cushioning and comfort.

Can I use a tire size calculator for any vehicle?

Yes, tire size calculators work for all vehicles including cars, trucks, SUVs, and motorcycles. However, always start from your vehicle's OEM specifications found on the door placard or owner's manual. The calculator helps you compare candidate sizes to the original, but final choices should be confirmed with a tire professional, especially for vehicles with advanced driver-assistance systems.

How much can I deviate from my original tire size?

The recommended guideline is to stay within ±3% of the original overall diameter. This helps maintain speedometer accuracy, preserve safety system calibration, and avoid clearance issues. Deviating more than 3% can affect vehicle handling, braking performance, and may require speedometer recalibration. Always consult with a tire professional for significant size changes.

Will changing tire size affect my fuel economy?

Yes, tire size changes can impact fuel economy. Larger, heavier tires require more energy to rotate, potentially reducing fuel efficiency. Additionally, changes in rolling diameter affect engine RPM at a given speed, which can influence fuel consumption. Wider tires also increase rolling resistance. However, the impact varies by vehicle and driving conditions.

Do I need to recalibrate my speedometer after changing tire sizes?

If you stay within the ±3% diameter difference, recalibration is usually not necessary. However, if you exceed this range, your speedometer will be inaccurate and recalibration is recommended. Some modern vehicles allow electronic speedometer recalibration, while others may require physical changes. Check with your vehicle manufacturer or a qualified technician for specific guidance.