1. What is a Gear Ratio Calculator for MPH?

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

Purpose: It helps automotive enthusiasts, mechanics, and engineers calculate vehicle speed 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)
• 336 — Constant combining unit conversions

Explanation: The formula calculates how fast your vehicle will go at a given RPM based on your tire size and gear ratio.

3. Importance of Gear Ratio Calculation

Details: Proper gear ratio selection affects acceleration, top speed, fuel economy, and engine performance. This calculation helps optimize these factors.

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 the ground to the top of the tire (loaded radius) and multiply by 2, or use manufacturer specifications.

Q2: What's the 336 constant in the formula?
A: It combines conversion factors for inches to miles (63360) and minutes to hours (60), simplified to 336 (63360/60/π).

Q3: Does this account for torque converter slip?
A: No, for automatic transmissions you may need to account for 5-10% converter slip in actual speed.

Q4: How accurate is this calculation?
A: It provides theoretical speed. Actual speed may vary due to tire growth at high speed, traction, and other factors.

Q5: Can I use this for different transmission gears?
A: Yes, but remember to multiply transmission gear ratio by final drive ratio for the total GR value.