Calculate Speed From RPM

Speed Formula:

\[ S = \frac{RPM \times \pi \times TD}{1056} \]

Speed (mph):

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1. What is Speed From RPM Calculator?

Definition: This calculator estimates vehicle speed based on engine RPM (revolutions per minute) and tire diameter.

Purpose: It helps automotive enthusiasts, mechanics, and engineers determine vehicle speed at specific RPM levels for gear ratio analysis and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ S = \frac{RPM \times \pi \times TD}{1056} \]

Where:

\( S \) — Speed (miles per hour)
\( RPM \) — Engine revolutions per minute
\( \pi \) — Mathematical constant (~3.14159)
\( TD \) — Tire diameter (inches)
1056 — Conversion factor (combining inches to miles and minutes to hours)

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

3. Importance of Speed-RPM Calculation

Details: Understanding the relationship between RPM and speed helps in gear ratio selection, fuel efficiency optimization, and performance tuning.

4. Using the Calculator

Tips: Enter the engine RPM and tire diameter in inches. For accurate results, measure the actual loaded tire diameter rather than using the nominal size.

5. Frequently Asked Questions (FAQ)

Q1: Why is the conversion factor 1056?
A: It combines 63,360 (inches per mile) divided by 60 (minutes per hour), simplifying to 1056 (63,360 ÷ 60 = 1056).

Q2: Does this account for gear ratios?
A: No, this assumes direct drive (1:1 ratio). For different gears, use the RPM at the wheels (engine RPM ÷ gear ratio).

Q3: 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: (wheel diameter) + (tire width × aspect ratio × 2 ÷ 25.4).

Q4: Why does my actual speed differ from the calculation?
A: Factors like tire slippage, inflation pressure, load, and transmission slip can affect actual speed. The calculation assumes perfect conditions.

Q5: Can I use this for different units?
A: For km/h, use the formula: \( S = \frac{RPM \times \pi \times TD}{1666.22} \) where TD is in inches, or adjust the conversion factor for mm tire diameter.