1. What is a Tire And Gear Ratio Calculator?

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

Purpose: It helps automotive enthusiasts and professionals determine vehicle speed at specific RPMs for gear ratio selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Speed (miles per hour)
• \( RPM \) — Engine revolutions per minute
• \( TD \) — Tire diameter (inches)
• \( GR \) — Gear ratio (unitless)
• \( 1056 \) — Conversion factor (combines inches to miles and minutes to hours)

Explanation: The formula calculates how far the vehicle travels per minute based on tire circumference and gear reduction, then converts to miles per hour.

3. Importance of Gear Ratio Calculation

Details: Proper gear ratio selection affects acceleration, top speed, fuel efficiency, and engine performance characteristics.

4. Using the Calculator

Tips: Enter engine RPM, measured tire diameter in inches, and gear ratio (including final drive ratio). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter accurately?
A: Measure from ground to top of tire under load, or calculate using: (wheel diameter) + 2*(section width*aspect ratio)/25.4.

Q2: What's included in the gear ratio?
A: Multiply transmission gear ratio by final drive ratio (differential ratio) for total gear reduction.

Q3: Why 1056 in the formula?
A: It converts inches per minute to miles per hour (63360 inches/mile ÷ 60 minutes/hour = 1056).

Q4: Does this account for tire slippage?
A: No, this is theoretical speed. Actual speed may vary due to traction conditions, transmission slippage, or tire growth at speed.

Q5: How does changing tire size affect speed?
A: Larger tires increase speed at same RPM (like higher gear ratio), while smaller tires decrease speed (like lower gear ratio).