1. What is the RPM Formula?

The RPM formula calculates engine revolutions per minute based on vehicle speed, gear ratio, and tire diameter. It's essential for understanding engine performance and gear selection.

2. How Does the Calculator Work?

The calculator uses the RPM equation:

Where:

• \( Speed \) — Vehicle speed in miles per hour (mph)
• \( Gear\ Ratio \) — Transmission gear ratio (dimensionless)
• \( Tire\ Diameter \) — Tire diameter in inches
• 336 — Constant to convert units

Explanation: The formula accounts for the relationship between wheel rotation and engine rotation through the gear ratio.

3. Importance of RPM Calculation

Details: Knowing engine RPM at different speeds helps with gear selection, fuel efficiency optimization, and preventing engine over-revving.

4. Using the Calculator

Tips: Enter speed in mph, gear ratio as a number (e.g., 3.73), and tire diameter in inches. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is 336 used in the formula?
A: 336 is a constant that combines unit conversions (5280 feet/mile, 12 inches/foot, 60 minutes/hour) and π (pi) to simplify the calculation.

Q2: How accurate is this calculation?
A: It provides a good estimate but actual RPM may vary slightly due to factors like tire wear, transmission slip, or converter clutch engagement.

Q3: Can I use this for metric units?
A: No, this formula is specifically for mph and inches. A different constant would be needed for km/h and mm.

Q4: What's a typical RPM range?
A: Most engines operate between 1,500-3,500 RPM at cruising speeds, with redlines typically between 5,000-7,000 RPM for passenger vehicles.

Q5: Does this work for all gear ratios?
A: Yes, but remember to use the current gear ratio (not final drive ratio unless you're in 1:1 gear).