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

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

Purpose: It helps automotive enthusiasts and mechanics select proper tire sizes when changing gear ratios or vice versa.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( TD \) — Tire diameter (inches)
• \( S \) — Vehicle speed (miles per hour)
• \( GR \) — Gear ratio (unitless)
• \( RPM \) — Engine revolutions per minute
• \( 1056 \) — Conversion constant (feet to inches and hours to minutes)
• \( \pi \) — Pi (approximately 3.1416)

Explanation: The formula calculates the tire diameter that will maintain your desired RPM at a specific speed with a given gear ratio.

3. Importance of Proper Tire Size Calculation

Details: Correct tire sizing ensures optimal engine performance, fuel efficiency, and speedometer accuracy when changing gear ratios.

4. Using the Calculator

Tips: Enter your desired cruising speed, gear ratio, and target RPM. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's the 1056 constant in the formula?
A: It converts mph to inches per minute (5280 feet/mile × 12 inches/foot ÷ 60 minutes/hour = 1056).

Q2: How accurate is this calculation?
A: It provides theoretical diameter. Actual results may vary slightly due to tire flex, traction, and other factors.

Q3: Can I use this for both metric and imperial units?
A: This version uses mph and inches. For metric, you'd need to adjust the formula (km/h and mm).

Q4: What's a typical gear ratio for street vehicles?
A: Most street cars have final drive ratios between 3.0 and 4.0, but this varies by vehicle type.

Q5: How does tire size affect performance?
A: Larger tires effectively lower gear ratio (higher top speed but slower acceleration), while smaller tires do the opposite.