1. What is a RPM to MPH Calculator?

Definition: This calculator converts rotational speed (RPM) to linear speed (MPH) based on tire diameter.

Purpose: It helps automotive enthusiasts, engineers, and mechanics determine vehicle speed from engine RPM and tire size.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Speed (miles per hour)
• \( RPM \) — Revolutions per minute
• \( TD \) — Tire diameter (inches)
• 336 — Conversion constant (combines unit conversions for inches to miles and minutes to hours)

Explanation: The formula calculates how much distance the tire covers in one minute, then converts it to miles per hour.

3. Importance of RPM to MPH Conversion

Details: Understanding this relationship helps in gear ratio selection, speedometer calibration, and performance tuning.

4. Using the Calculator

Tips: Enter the engine RPM and tire diameter in inches. The tire diameter should be the overall diameter including tread.

5. Frequently Asked Questions (FAQ)

Q1: Where does the 336 constant come from?
A: It combines 5280 (feet per mile) × 12 (inches per foot) ÷ 60 (minutes per hour) = 1056, then divided by π (3.1416) ≈ 336.

Q2: How do I measure tire diameter accurately?
A: Measure from the ground to the top of the tire, or calculate from tire size markings (e.g., 225/45R17).

Q3: Does this account for gear ratios?
A: No, this calculates theoretical speed at the wheels. For actual vehicle speed, use driveshaft RPM instead of engine RPM.

Q4: Why is my actual speed different?
A: Factors like tire wear, inflation pressure, load, and slippage can affect actual speed.

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