1. What is a Gear Ratio 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 vehicle speed at specific RPMs for gear 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 constant (combines inches to miles and minutes to hours)

Explanation: The formula calculates how far the vehicle travels per minute based on wheel rotation, then converts this to miles per hour.

3. Importance of Gear Ratio and Tire Size Calculation

Details: Proper gear ratio selection affects acceleration, top speed, fuel efficiency, and engine performance. Tire size changes effectively alter the final drive ratio.

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: How do I measure tire diameter?
A: Measure from ground to top of tire when properly inflated, or calculate using tire size markings (e.g., 275/60R15).

Q2: What gear ratio should I include?
A: Multiply transmission gear ratio by final drive ratio (e.g., 4th gear 1:1 with 3.73 rear end = 3.73 total ratio).

Q3: Why is the result not matching my actual speed?
A: Variations can occur due to tire flex, converter slip (automatics), or inaccurate measurements.

Q4: How does tire size affect speed?
A: Larger tires increase speed per RPM but reduce torque; smaller tires do the opposite.

Q5: What's a typical gear ratio for highway driving?
A: Most vehicles use 2.5-3.5:1 final drive ratios for balanced performance and economy.