1. What is a Gear and 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 tire and gear combinations.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Vehicle speed (mph)
• \( RPM \) — Engine revolutions per minute
• \( TD \) — Tire diameter (inches)
• \( GR \) — Gear ratio (unitless)
• \( 1056 \) — Conversion constant (combines unit conversions)

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 and Tire Calculations

Details: Proper calculations ensure optimal performance, fuel efficiency, and prevent engine strain from improper gearing.

4. Using the Calculator

Tips: Enter engine RPM, tire diameter in inches, and gear ratio (default 3.73). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter?
A: Measure from ground to top of tire or calculate using: (Width * Aspect Ratio / 1270) + Wheel Diameter.

Q2: What's a typical gear ratio?
A: Most vehicles range from 2.73 (highway) to 4.10 (performance/towing), with 3.23-3.73 being common.

Q3: Does this account for torque converter slip?
A: No, automatic transmissions may show slightly lower actual speeds due to converter slip (typically 2-5%).

Q4: How accurate is this calculation?
A: Very accurate for manual transmissions; automatic transmissions may vary slightly due to slip.

Q5: Can I use this for different transmission gears?
A: Yes, but remember to use the gear ratio for the specific gear you're calculating (not just final drive).