1. What is a Gear Ratio Speed Calculator?

Definition: This calculator estimates vehicle speed based on engine RPM, tire diameter, and gear ratio.

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

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Vehicle speed (mph)
• \( RPM \) — Engine revolutions per minute
• \( TD \) — Tire diameter (inches)
• \( GR \) — Gear ratio (unitless)
• \( 1056 \) — Conversion factor (combines inches to miles and minutes to hours)

Explanation: The formula calculates how far the vehicle travels per minute based on tire circumference and gear reduction, then converts to miles per hour.

3. Importance of Gear Ratio Calculations

Details: Proper gear ratio selection affects acceleration, top speed, fuel efficiency, and engine performance characteristics.

4. Using the Calculator

Tips: Enter engine RPM, tire diameter in inches, and gear ratio (e.g., 3.73 for a common rear axle ratio). 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 (loaded) or calculate from tire size markings (e.g., 275/60R15 = ~28" diameter).

Q2: What gear ratio should I use?
A: Lower ratios (3.08) favor highway cruising, higher ratios (4.10) favor acceleration. Consider engine power and intended use.

Q3: Does this account for torque converter slip?
A: No, automatic transmissions may show slightly lower actual speeds due to converter slip (typically 2-5%).

Q4: How accurate is this calculator?
A: It provides theoretical speed. Actual speed may vary due to tire growth at speed, traction conditions, and drivetrain losses.

Q5: Can I use this for motorcycle or bicycle calculations?
A: Yes, the formula works for any wheeled vehicle. Just input appropriate values for RPM, tire size, and gear ratio.