1. What is a Speed Calculator from RPM and Tire Size?

Definition: This calculator estimates vehicle speed based on engine RPM and tire diameter.

Purpose: It helps automotive professionals, mechanics, and enthusiasts determine vehicle speed at specific engine RPMs for gear ratio analysis 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
• \( \pi \) — Pi (approximately 3.1416)
• \( TD \) — Tire diameter (inches)
• 1056 — Conversion factor (combines unit conversions for mph)

Explanation: The formula calculates how much distance the vehicle travels per minute based on tire circumference and RPM, then converts to miles per hour.

3. Importance of Speed Calculation

Details: Accurate speed calculations help in gear ratio selection, transmission tuning, and verifying speedometer accuracy.

4. Using the Calculator

Tips: Enter the engine RPM and tire diameter in inches. For accurate results, measure tire diameter when properly inflated and under load.

5. Frequently Asked Questions (FAQ)

Q1: What's the 1056 conversion factor?
A: It combines conversions from inches to miles (63360), minutes to hours (60), and simplifies the equation (63360/60 = 1056).

Q2: How do I measure tire diameter?
A: Measure from ground to top of tire under load, or calculate from tire size markings (e.g., 225/45R17: diameter = (225×0.45×2)/25.4 + 17).

Q3: Does this account for gear ratios?
A: No, this assumes direct 1:1 drive ratio. For other gears, use RPM at the wheels (divide engine RPM by gear ratio).

Q4: Why is my actual speed different?
A: Factors like tire slip, transmission slippage, and load can affect actual speed. This is a theoretical calculation.

Q5: Can I use this for different units?
A: For km/h, replace 1056 with 1666. For meters/second, use different conversion factors.