1. What is the Auto Gear Ratio Calculator?

The Auto Gear Ratio Calculator with Tire Size estimates vehicle speed (MPH) based on engine RPM, tire diameter, and gear ratio. This helps automotive enthusiasts and mechanics understand vehicle performance characteristics.

2. How Does the Calculator Work?

The calculator uses the following equation:

Where:

• \( RPM \) — Engine revolutions per minute
• \( tire\_dia\_in \) — Tire diameter in inches
• \( GR \) — Gear ratio (dimensionless)
• 336 — Conversion factor combining several unit conversions

Explanation: The equation accounts for the relationship between engine speed, tire size, and final drive ratio to determine vehicle speed.

3. Importance of Gear Ratio Calculation

Details: Understanding the relationship between RPM and speed helps with gear selection, fuel efficiency optimization, and performance tuning.

4. Using the Calculator

Tips: Enter RPM (typically between 1000-7000 for most vehicles), accurate tire diameter (measured or from manufacturer specs), and gear ratio (including final drive ratio). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure my tire diameter?
A: Measure from ground to top of tire (loaded) or calculate from tire size markings (e.g., 225/45R17 has ~25" diameter).

Q2: What is a typical gear ratio?
A: Final drive ratios typically range from 2.73 to 4.10 for passenger vehicles, with higher numbers for performance/towing.

Q3: Does this account for torque converter slip?
A: No, this calculates theoretical speed. Automatic transmissions may show slightly lower actual speeds due to converter slip.

Q4: Can I use this for motorcycle calculations?
A: Yes, the formula works for any wheeled vehicle when using proper tire diameter and gear ratio.

Q5: Why is 336 the conversion factor?
A: It combines conversions for inches to miles, minutes to hours, and accounts for pi in circumference calculations.