Tire Size Calculator - Compare Tire Dimensions & Speedometer Error
Free online tire size calculator to compare current and new tire dimensions, revolutions per mile, and estimate speedometer error for accurate vehicle modifications.
Tire Size Comparison
Results
What is a Tire Size Calculator?
A Tire Size Calculator is a free automotive tool that helps you compare the specifications of different tire sizes. It determines key dimensions like overall diameter and revolutions per mile, and calculates the potential speedometer error when you change tire sizes.
This calculator is essential for:
- Vehicle Modification - Ensuring new tires fit and perform correctly.
- Speedometer Accuracy - Understanding how tire changes affect your vehicle's speed readings.
- Performance Tuning - Analyzing the impact of tire size on gearing and acceleration.
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How the Tire Size Calculator Works
The calculator uses standard tire measurement formulas:
Where:
- Tire Width = The width of the tire in millimeters (e.g., 205).
- Aspect Ratio = The height of the sidewall as a percentage of the tire's width (e.g., 55%).
- Wheel Diameter = The diameter of the wheel in inches (e.g., 16).
- π (Pi) = Approximately 3.14159.
- 63360 = Number of inches in a mile.
Key Concepts Explained
Tire Width (mm)
The measurement of the tire from sidewall to sidewall in millimeters.
Aspect Ratio (%)
The height of the tire's sidewall, expressed as a percentage of the tire's width.
Wheel Diameter (in)
The diameter of the wheel (rim) in inches, on which the tire is mounted.
Overall Diameter
The total height of the tire when inflated, from the top of the tread to the bottom.
Revolutions Per Mile (RPM)
The number of rotations a tire makes to travel one mile. Affects gearing and speedometer.
Speedometer Error
The percentage difference between your actual speed and the speed displayed on your speedometer due to a change in tire diameter.
How to Use This Calculator
Enter Current Tire Specs
Input the width, aspect ratio, and wheel diameter of your current tires.
Enter New Tire Specs
Input the width, aspect ratio, and wheel diameter of the new tires you are considering.
Get Results
View the overall diameter and revolutions per mile for both tires, plus the speedometer error.
Benefits of Using This Calculator
- • Accurate Comparison: Quickly compare two tire sizes side-by-side to understand their differences.
- • Prevent Speedometer Errors: Identify potential speedometer inaccuracies before installing new tires.
- • Informed Decisions: Make better choices for tire upgrades, ensuring compatibility and optimal vehicle performance.
Factors That Affect Your Results
1. Tire Width (mm)
A wider tire generally increases the overall diameter if the aspect ratio remains constant.
2. Aspect Ratio (%)
A higher aspect ratio means a taller sidewall, increasing the overall tire diameter.
3. Wheel Diameter (in)
A larger wheel diameter directly increases the overall tire diameter.
4. Tire Pressure
While not an input, proper tire inflation significantly impacts the actual rolling diameter and revolutions per mile.
Frequently Asked Questions (FAQ)
Q: What is a tire size calculator?
A: A tire size calculator is a tool that helps you compare the dimensions and performance characteristics of different tire sizes. It calculates metrics like overall diameter, sidewall height, and revolutions per mile, and estimates speedometer error when changing tire sizes.
Q: How do I read tire size numbers?
A: Tire sizes are typically displayed as a series of numbers and letters, e.g., 205/55R16. '205' is the tire width in millimeters, '55' is the aspect ratio (sidewall height as a percentage of width), and '16' is the wheel diameter in inches.
Q: Why is speedometer error important?
A: Changing tire sizes can affect your speedometer's accuracy. If the new tire's diameter is significantly different, your speedometer might show a speed higher or lower than your actual speed, which can lead to speeding tickets or inaccurate mileage tracking.
Q: What is revolutions per mile?
A: Revolutions per mile (RPM) is the number of times a tire rotates to cover one mile. This value is crucial for understanding how a tire change affects gearing and speedometer accuracy.