1. What is a Gear Ratio To RPM Calculator?

Definition: This calculator estimates engine RPM (revolutions per minute) based on vehicle speed, gear ratio, and tire diameter.

Purpose: It helps automotive enthusiasts, mechanics, and engineers determine engine speed for gear selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( RPM \) — Engine revolutions per minute
• \( S \) — Vehicle speed (miles per hour)
• \( GR \) — Gear ratio (unitless)
• \( TD \) — Tire diameter (inches)
• \( 1056 \) — Conversion constant (combining various unit conversions)

Explanation: The formula converts vehicle speed through the gear reduction and tire circumference to determine engine rotation speed.

3. Importance of RPM Calculation

Details: Knowing engine RPM helps optimize gear selection, improve fuel efficiency, prevent over-revving, and maximize performance.

4. Using the Calculator

Tips: Enter the vehicle speed in mph, gear ratio (e.g., 3.73 for a common rear axle ratio), and tire diameter in inches. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's the 1056 constant in the formula?
A: It combines conversions for mph to inches per minute (63360) and accounts for the 60 minutes in an hour (63360/60 = 1056).

Q2: How do I measure tire diameter accurately?
A: Measure from ground to top of tire (loaded) or calculate using: (wheel diameter) + 2*(sidewall height).

Q3: Does this include torque converter slip in automatics?
A: No, for automatic transmissions you may need to add 5-10% to account for converter slip under load.

Q4: What's a typical gear ratio range?
A: Final drive ratios typically range from 2.73 (highway gears) to 4.56 (performance/towing gears).

Q5: How can I use this for gear selection?
A: Compare RPM at desired cruising speed with your engine's power band to choose optimal gears.