1. What is a Gear and Tire Calculator?

Definition: This calculator determines the gear ratio based on engine RPM, tire diameter, vehicle speed, and final drive ratio.

Purpose: It helps automotive enthusiasts and mechanics optimize vehicle performance by calculating the ideal gear ratio for given parameters.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( GR \) — Gear Ratio (dimensionless factor)
• \( RPM \) — Engine revolutions per minute
• \( TD \) — Tire diameter (inches)
• \( MPH \) — Vehicle speed (miles per hour)
• \( FD \) — Final drive ratio (factor)
• 336 — Constant for unit conversion

Explanation: The formula calculates the transmission gear ratio needed to achieve a specific RPM at a given speed with particular tires and final drive.

3. Importance of Gear Ratio Calculation

Details: Proper gear ratio selection affects acceleration, fuel economy, towing capacity, and overall vehicle performance.

4. Using the Calculator

Tips: Enter engine RPM, tire diameter in inches, vehicle speed in MPH, and final drive ratio (default 1.0). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's the significance of the 336 constant?
A: It converts units from inches and miles to revolutions per hour (5280 ft/mi × 12 in/ft ÷ 60 min/hr ≈ 336).

Q2: How do I measure tire diameter accurately?
A: Measure from ground to top of tire under load, or use manufacturer specs for unloaded diameter.

Q3: What if I have an overdrive transmission?
A: Include the overdrive ratio in your final drive calculation (e.g., 0.7 overdrive × 3.73 axle = 2.611 effective ratio).

Q4: Why does gear ratio matter for performance?
A: Lower ratios provide better acceleration, higher ratios improve fuel economy at highway speeds.

Q5: Can I use this for transmission gear selection?
A: Yes, this helps determine ideal transmission ratios when combined with axle ratio and tire size.