1. What is an RPM to MPH Converter?

Definition: This calculator converts engine RPM (revolutions per minute) to vehicle speed in MPH (miles per hour) based on tire diameter.

Purpose: It helps automotive enthusiasts, mechanics, and engineers understand the relationship between engine speed and vehicle speed.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Speed (miles per hour)
• \( RPM \) — Engine revolutions per minute
• \( TD \) — Tire diameter (inches)
• 336 — Constant that combines unit conversions

Explanation: The formula accounts for tire circumference and converts inches per minute to miles per hour.

3. Importance of RPM to MPH Conversion

Details: Understanding this relationship helps with gear ratio selection, fuel efficiency optimization, and performance tuning.

4. Using the Calculator

Tips: Enter the engine RPM and tire diameter in inches. For accurate results, measure the actual loaded tire diameter rather than using the nominal size.

5. Frequently Asked Questions (FAQ)

Q1: Where does the constant 336 come from?
A: It combines unit conversions (5280 feet/mile × 12 inches/foot ÷ 60 minutes/hour ≈ 336).

Q2: Does this account for gear ratios?
A: No, this assumes direct 1:1 drive ratio. For real vehicles, multiply by the overall gear ratio (transmission × differential).

Q3: How do I measure tire diameter accurately?
A: Measure from the ground to the center of the wheel and multiply by 2, with the vehicle's normal load.

Q4: Why is my actual speed different from the calculation?
A: Factors like tire slippage, gear ratios, transmission slip, and speedometer calibration can affect real-world results.

Q5: Can I use this for different wheel sizes?
A: Yes, just input the actual diameter of any wheel/tire combination.