1. What is a Gear Ratio Calculator for Tire Size?

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 proper 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 (combines unit conversions)

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 ensures optimal engine performance, fuel efficiency, and prevents over-revving or lugging the engine.

4. Using the Calculator

Tips: Enter the engine RPM at cruise, your actual tire diameter (measured is best), and desired cruising speed. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is tire diameter important in gear ratio?
A: Larger tires effectively create a taller gear ratio, while smaller tires create a shorter ratio, affecting engine RPM at any given speed.

Q2: What's a typical gear ratio range?
A: Most vehicles range from 2.73:1 to 4.10:1, with performance vehicles sometimes using ratios up to 5.13:1.

Q3: How do I measure my actual tire diameter?
A: Measure from ground to top of tire with vehicle at normal weight, or calculate using: (Width × Aspect Ratio × 2 / 25.4) + Wheel Diameter.

Q4: What RPM should I use for calculations?
A: Use your engine's optimal cruising RPM (typically where it makes good torque without excessive fuel consumption).

Q5: Does this account for transmission gear?
A: No, this calculates final drive ratio. Multiply by transmission gear ratio for complete engine-to-wheel ratio.