1. What is a Gear Ratio Speed Calculator?

Definition: This calculator estimates vehicle speed in miles per hour based on engine RPM, tire diameter, gear ratio, and final drive ratio.

Purpose: It helps automotive enthusiasts, mechanics, and engineers determine vehicle speed at specific RPMs for gear selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \text{MPH} \) — Vehicle speed (miles per hour)
• \( \text{RPM} \) — Engine revolutions per minute
• \( \text{TD} \) — Tire diameter (inches)
• \( \text{GR} \) — Transmission gear ratio
• \( \text{FD} \) — Final drive (differential) ratio
• 336 — Constant to convert units to MPH

Explanation: The formula calculates how much distance the vehicle travels per engine revolution based on tire size and gear reduction.

3. Importance of Speed Calculation

Details: Accurate speed calculations help optimize gear ratios for performance, fuel efficiency, and proper engine operation within its power band.

4. Using the Calculator

Tips: Enter engine RPM, tire diameter (measured from ground to top of tire), current gear ratio, and final drive ratio. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire diameter accurately?
A: Measure from the ground to the top of the tire with the vehicle's weight on it, or calculate using tire size markings (e.g., 275/60R15).

Q2: What's the 336 constant in the formula?
A: It combines unit conversions (inches to miles, minutes to hours) and π (pi) for circumference calculation.

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

Q4: Where can I find my gear ratios?
A: Check your vehicle's service manual or manufacturer specifications for gear and final drive ratios.

Q5: Can I use this for different speed units?
A: This calculates MPH. For KPH, multiply the result by 1.60934.