1. What is Speed From Gear Ratio Calculator?

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

Purpose: It helps automotive enthusiasts and professionals determine vehicle speed at specific RPM points for gear selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Speed (mph)
• \( RPM \) — Engine revolutions per minute
• \( TD \) — Tire diameter (inches)
• \( GR \) — Gear ratio (unitless)
• \( AR \) — Axle ratio (unitless)

Explanation: The formula calculates how fast the vehicle moves based on how fast the engine is turning, the tire size, and the gear reduction ratios.

3. Importance of Speed Calculation

Details: Accurate speed calculation helps in gear selection, performance tuning, fuel efficiency optimization, and ensuring speedometer accuracy.

4. Using the Calculator

Tips: Enter RPM, tire diameter in inches, gear ratio, and axle ratio. All values must be > 0. Typical axle ratios range from 2.73 to 4.10 for passenger vehicles.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter?
A: Measure from the ground to the top of the tire (loaded radius) and multiply by 2, or use manufacturer specifications.

Q2: What's a typical gear ratio?
A: Transmission gear ratios vary: 1st gear might be 2.66-3.97:1, while overdrive might be 0.67-0.85:1.

Q3: Why is the axle ratio important?
A: The axle ratio provides final gear reduction after the transmission, affecting both acceleration and cruising RPM.

Q4: How accurate is this calculation?
A: It's theoretical - actual speed may vary due to tire slip, wear, inflation, and drivetrain losses.

Q5: Can I use this for different units?
A: This version uses inches and mph. For metric units, conversion would be needed.