1. What is RPM to MPH Calculator?

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

Purpose: It helps automotive enthusiasts, mechanics, and engineers determine vehicle speed at specific RPM levels for gear tuning and performance analysis.

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)
• \( GR \) — Gear ratio (unitless)
• 336 — Constant combining unit conversions

Explanation: The formula accounts for how many times the tire rotates per minute (based on gear ratio) and converts that to linear distance traveled per hour.

3. Importance of RPM to MPH Calculation

Details: Understanding the relationship between RPM and speed helps in gear selection, fuel efficiency optimization, and performance tuning.

4. Using the Calculator

Tips: Enter the engine RPM, tire diameter (measured from ground to top of tire), and gear ratio (default 3.73). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is 336 used in the formula?
A: It combines conversion factors for inches to miles (63,360) and minutes to hours (60) divided by π (3.1416): (63360)/(60*π) ≈ 336.

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

Q3: What affects the gear ratio value?
A: Transmission gear, differential ratio, and transfer case ratio (for 4WD) all contribute to the final drive ratio.

Q4: Does this account for tire slippage?
A: No, this calculates theoretical speed. Actual speed may vary due to tire slip, wear, or inflation.

Q5: How can I use this for gear selection?
A: Compare speed at redline RPM with different gear ratios to optimize acceleration or top speed.