1. What is Speedometer Size?

The speedometer size factor indicates how much the speedometer reading needs to be adjusted based on the difference between the effective diameter (current tire size) and actual diameter (original tire size).

2. How Does the Calculator Work?

The calculator uses the speedometer size formula:

Where:

• \( Effective\_Dia \) — Diameter of current tires (inches)
• \( Actual\_Dia \) — Diameter of original tires (inches)
• \( Reading \) — Speedometer reading (mph)

Explanation: The equation calculates the correction factor needed when changing tire sizes to maintain accurate speedometer readings.

3. Importance of Correct Speedometer Size

Details: Accurate speedometer readings are crucial for maintaining proper vehicle speed, avoiding speeding tickets, and ensuring odometer accuracy.

4. Using the Calculator

Tips: Measure both your original and current tire diameters carefully. Enter all values in inches except speed which is in mph. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why does tire size affect speedometer accuracy?
A: Larger tires rotate fewer times per mile than smaller tires, causing the speedometer to read slower than actual speed if not corrected.

Q2: How do I measure tire diameter?
A: Measure from the ground to the top of the tire (while loaded) and multiply by 2, or use manufacturer specifications.

Q3: What's a typical speedometer size factor?
A: For stock vehicles, the factor is typically close to 1.0. Modified vehicles might range from 0.9 to 1.2 depending on tire changes.

Q4: Does this affect odometer readings?
A: Yes, the same correction factor applies to odometer readings as they use the same speed sensor data.

Q5: Can I use this for metric measurements?
A: The calculator works with any consistent units, but the formula assumes all diameter measurements are in the same unit (inches or mm).