1. What is Pulse Per Mile?

Pulse Per Mile (PPM) is a measurement used to calibrate speedometers by calculating the number of electronic pulses generated per mile traveled. This ensures accurate speed and distance readings.

2. How Does the Calculator Work?

The calculator uses the PPM equation:

Where:

• 63360 — Inches in one mile
• π — Mathematical constant Pi (~3.1416)
• Tire Diameter — Height of tire in inches
• Axle Ratio — Gear ratio of the vehicle's differential
• Teeth — Number of teeth on the speed sensor gear

Explanation: The equation calculates how many times the speed sensor will pulse based on tire revolutions per mile, gear reduction, and sensor gear teeth.

3. Importance of PPM Calculation

Details: Accurate PPM calculation is crucial for proper speedometer calibration, especially after changing tire sizes, gear ratios, or speed sensor gears.

4. Using the Calculator

Tips: Enter tire diameter in inches, axle ratio as a number (e.g., 3.73), and number of teeth on the speed sensor gear. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter?
A: Measure from the ground to the top of the tire (loaded radius) and multiply by 2, or use manufacturer specifications.

Q2: Where can I find my axle ratio?
A: Check your vehicle's specifications, door jamb sticker, or differential tag. It's often between 2.73 and 4.10 for most vehicles.

Q3: What if I don't know the teeth count?
A: You may need to physically count them or consult your vehicle's service manual. Common counts are between 7-45 teeth.

Q4: Why does PPM matter for speedometer accuracy?
A: The speedometer relies on these pulses to calculate speed. Wrong PPM = wrong speed reading.

Q5: How precise does this need to be?
A: For most applications, within 5% is acceptable, but precision is better for accurate odometer readings.