1. What is the Wallace RPM Gear Calculator?

The Wallace RPM Gear Calculator estimates engine revolutions per minute (RPM) based on vehicle speed, gear ratio, and tire diameter. This calculation is essential for automotive performance tuning and gear selection.

2. How Does the Calculator Work?

The calculator uses the Wallace RPM formula:

Where:

• \( RPM_{wrg} \) — Engine revolutions per minute
• \( Speed_w \) — Vehicle speed in miles per hour
• \( GR_w \) — Gear ratio (unitless)
• \( D_{tire_w} \) — Tire diameter in inches

Explanation: The constant 336 converts units to provide RPM result. This formula assumes direct drive without torque converter slip.

3. Importance of RPM Calculation

Details: Accurate RPM calculation helps optimize gear selection, improve fuel efficiency, prevent engine over-revving, and maximize performance in racing applications.

4. Using the Calculator

Tips: Enter vehicle speed in MPH, gear ratio (typically between 2.0-4.0 for most vehicles), and measured tire diameter in inches. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is the constant 336 used in the formula?
A: The constant 336 combines unit conversion factors (5280 feet/mile, 12 inches/foot, 60 minutes/hour) divided by π (3.1416).

Q2: How do I measure tire diameter accurately?
A: Measure from ground to top of tire with vehicle weight on it, or calculate using tire size markings (e.g., 275/60R15 = [(275×0.60×2)/25.4] + 15).

Q3: Does this account for torque converter slip in automatics?
A: No, this formula calculates theoretical RPM. Actual RPM may be higher due to torque converter slip in automatic transmissions.

Q4: What is a typical gear ratio range?
A: Final drive ratios typically range from 2.73 to 4.10 for street vehicles, with higher numbers for performance applications.

Q5: Can I use this for metric measurements?
A: The formula is designed for imperial units. Convert km/h to MPH (divide by 1.609) and mm to inches (divide by 25.4) for metric inputs.