Gear Ratio Speed Calculator Formula

Gear Ratio Speed Formula:

\[ S = \frac{RPM \times TD}{GR \times 336} \]

Vehicle Speed (mph):

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1. What is a Gear Ratio Speed Calculator?

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

Purpose: It helps automotive enthusiasts and mechanics determine theoretical vehicle speed for given gearing and RPM.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ S = \frac{RPM \times TD}{GR \times 336} \]

Where:

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

Explanation: The formula calculates how far the vehicle travels per minute based on tire circumference and gear reduction, then converts to miles per hour.

3. Importance of Gear Ratio Calculations

Details: Proper gearing calculations ensure optimal performance, fuel efficiency, and prevent engine over-revving.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What does the 336 constant represent?
A: It combines unit conversions (inches to miles and minutes to hours) with the π calculation for tire circumference.

Q2: How do I measure tire diameter?
A: Measure from ground to top of tire under load, or use manufacturer specs for unloaded diameter.

Q3: Does this account for transmission gear ratios?
A: No, this calculates final speed based on the final drive ratio. Multiply transmission gear ratio by final drive ratio for complete calculation.

Q4: Why might actual speed differ?
A: Tire slip, transmission efficiency, wind resistance, and load can affect actual speed.

Q5: How accurate is this calculation?
A: It provides theoretical speed. Actual speed may vary by 1-5% due to various factors.