1. What is Speedometer Correction?

Speedometer correction is necessary when changing tire sizes to maintain accurate speed and distance readings. The correction factor accounts for the difference in tire diameters between old and new tires.

2. How Does the Calculator Work?

The calculator uses the speedometer correction formula:

Where:

• \( New\ Tire\ Diameter \) — Diameter of the new tire (inches)
• \( Old\ Tire\ Diameter \) — Diameter of the original tire (inches)

Explanation: When your new tires are larger than the original tires, your speedometer will read slower than your actual speed. When they're smaller, it will read faster.

3. Importance of Speedometer Correction

Details: Accurate speedometer readings are crucial for maintaining proper vehicle speed, calculating fuel economy, and ensuring odometer accuracy. Incorrect readings can lead to speeding tickets or inaccurate maintenance schedules.

4. Using the Calculator

Tips: Enter both new and old tire diameters in inches. Measure from the ground to the top of the tire when properly inflated and under normal load. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter?
A: The most accurate method is to measure from the ground to the top of the tire when properly inflated and under normal load.

Q2: What if I only know the tire size code?
A: You can calculate diameter from the tire code (e.g., 235/75R15) using online calculators or specific formulas.

Q3: How does this affect my odometer?
A: The odometer uses the same signal as the speedometer, so it will be equally affected by tire size changes.

Q4: Can I adjust my speedometer?
A: Many modern vehicles allow speedometer calibration through the ECU. Some require aftermarket calibration devices.

Q5: What's a typical correction factor?
A: Most tire changes result in correction factors between 0.95 and 1.05. Factors outside this range may require special attention.