1. What is a Gearing Tire Size Calculator?

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

Purpose: It helps automotive enthusiasts and mechanics determine speed at specific RPMs for different gear and tire combinations.

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)

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 Gearing Calculations

Details: Proper gearing ensures optimal engine performance, fuel efficiency, and desired speed characteristics for different applications.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

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

Q2: How do I measure tire diameter?
A: Measure from ground to top of tire or calculate from tire size markings (e.g., 275/60R15 = ((275×0.60×2)/25.4)+15).

Q3: Does this account for tire slip or deformation?
A: No, this is theoretical speed. Actual speed may vary due to tire slip, wear, or load.

Q4: What's a typical gear ratio?
A: Varies by vehicle, but common final drive ratios range from 2.73 to 4.10 for street vehicles.

Q5: Can I use this for transmission gear selection?
A: Yes, multiply transmission gear ratio by final drive ratio for total GR in each gear.