1. What is an RPM to MPH Calculator?

Definition: This calculator estimates vehicle speed in miles per hour based on engine RPM, tire size, gear ratio, and axle ratio.

Purpose: It helps automotive enthusiasts and mechanics determine speed at specific RPMs for gear selection and performance tuning.

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)
• \( GR \) — Transmission gear ratio
• \( AR \) — Axle ratio

Explanation: The formula converts engine rotation through the drivetrain to linear speed, accounting for tire circumference and gear reductions.

3. Importance of RPM to MPH Calculation

Details: Accurate speed calculation helps with gear selection, fuel efficiency optimization, and performance tuning.

4. Using the Calculator

Tips: Enter engine RPM, tire diameter in inches, current gear ratio (1.0 for direct drive), and axle ratio (default 3.73). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter?
A: Measure from ground to top of tire or calculate from tire size markings (e.g., 275/60R15 ≈ 28" diameter).

Q2: What's a typical axle ratio?
A: Common ratios range from 3.08 (highway) to 4.10 (performance), with 3.73 being a popular all-around ratio.

Q3: Why is 1056 in the formula?
A: This constant converts inches per minute to miles per hour (12 in/ft × 5280 ft/mile ÷ 60 min/hour).

Q4: Does this account for tire slippage?
A: No, this is theoretical speed. Actual speed may vary due to traction conditions and transmission slip.

Q5: How accurate is this calculator?
A: Very accurate for theoretical calculations, but real-world factors like tire wear and inflation can affect actual speed.