1. What is a Gear Ratio RPM Speed 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 and vehicle speed for different gear ratios.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Speed (mph)
• \( RPM \) — Engine revolutions per minute
• \( TD \) — Tire diameter (inches)
• \( GR \) — Gear ratio (unitless)

Explanation: The formula accounts for how tire size and gear reduction affect the vehicle's speed at a given engine RPM.

3. Importance of Gear Ratio Calculations

Details: Proper gear ratio selection affects acceleration, fuel economy, top speed, and engine longevity.

4. Using the Calculator

Tips: Enter engine RPM, tire diameter in inches, and gear ratio (e.g., 3.73 for common rear-end ratios). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is the 336 constant in the formula?
A: This combines unit conversions (inches to miles, minutes to hours) and pi (π) for circumference calculations.

Q2: How do I measure tire diameter?
A: Measure from ground to top of tire (loaded) or use manufacturer specs. For more accuracy, use revs/mile data.

Q3: Does this include torque converter slip?
A: No, this calculates theoretical speed. For automatics, reduce calculated speed by 3-8% to account for slip.

Q4: What's a typical gear ratio?
A: Varies by vehicle: 2.73-3.23 for economy cars, 3.55-4.10 for trucks/tow vehicles, 4.56+ for off-road.

Q5: Can I use this for transmission gear calculations?
A: Yes, multiply final drive ratio by transmission gear ratio (e.g., 4th gear 1:1 × rear end 3.73 = 3.73 total ratio).