1. What is a RPM Vs Gear Ratio Calculator?

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

Purpose: It helps automotive enthusiasts and mechanics understand the relationship between engine speed, gearing, and actual vehicle speed.

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 factor (combines unit conversions)

Explanation: The formula calculates how fast your vehicle is moving based on how fast your engine is turning, the size of your tires, and your gear reduction.

3. Importance of RPM/Gear Ratio Calculations

Details: Understanding this relationship helps with gear selection, fuel efficiency optimization, and performance tuning.

4. Using the Calculator

Tips: Enter your engine RPM, accurate tire diameter (measured or from specs), and gear ratio (including final drive ratio). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure my tire diameter?
A: Measure from ground to top of tire (loaded) or use the formula: (wheel diameter) + (tire width * aspect ratio / 100 * 2 / 25.4).

Q2: What gear ratio should I use?
A: Multiply transmission gear ratio by final drive ratio. For example, 4th gear (1:1) with 3.73 rear end = 3.73 overall ratio.

Q3: Why 1056 in the formula?
A: This converts inches/minute to miles/hour (12 in/ft × 5280 ft/mile ÷ 60 min/hour ≈ 1056).

Q4: Does this account for torque converter slip?
A: No, for automatics you may need to add 5-10% to RPM to account for converter slip.

Q5: How accurate is this calculation?
A: Very accurate if inputs are correct, but actual speed may vary slightly due to tire flex, wear, and other factors.