1. What is a Tire Size Gear Ratio Calculator?

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

Purpose: It helps automotive enthusiasts and mechanics select the right gear ratio when changing tire sizes or transmission components.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

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

Explanation: The formula calculates how many times the driveshaft rotates for each wheel revolution at a given speed and RPM.

3. Importance of Gear Ratio Calculation

Details: Proper gear ratio selection maintains engine performance, fuel efficiency, and correct speedometer readings when changing tire sizes.

4. Using the Calculator

Tips: Enter the engine RPM at cruising speed, your tire diameter (measured or from specs), and desired vehicle speed. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is gear ratio important when changing tire size?
A: Larger tires effectively change your final drive ratio, which can affect acceleration, towing capacity, and fuel economy.

Q2: How do I measure my tire diameter?
A: Measure from ground to top of tire (inflated) or calculate using sidewall numbers: (width * aspect ratio / 1270) + wheel diameter.

Q3: What's a typical gear ratio range?
A: Most vehicles range from 2.73 to 4.10, with lower numbers for fuel efficiency and higher for towing/performance.

Q4: Does this account for transmission gear?
A: This calculates final drive ratio. For specific gears, multiply by transmission gear ratio.

Q5: What if my speedometer is off after tire changes?
A: This calculator helps determine needed gear ratio adjustments to correct speedometer readings.