Gear Ratio Speed Calculator MPH RPM

Speed Formula:

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

RPM:

RPM

Tire Diameter:

inches

Gear Ratio:

Axle Ratio:

Speed (mph):

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1. What is a Gear Ratio Speed Calculator?

Definition: This calculator determines vehicle speed in miles per hour (mph) based on engine RPM, tire diameter, gear ratio, and axle ratio.

Purpose: It helps automotive enthusiasts, mechanics, and engineers calculate theoretical vehicle speed for gear selection and performance tuning.

2. How Does the Calculator Work?

The calculator uses the formula:

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

Where:

\( S \) — Speed (mph)
\( RPM \) — Engine revolutions per minute
\( TD \) — Tire diameter (inches)
\( GR \) — Gear ratio (unitless)
\( AR \) — Axle ratio (unitless)
1056 — Conversion constant for units

Explanation: The formula calculates how fast a vehicle moves based on how fast the engine is turning (RPM), the tire size, and the gear reduction ratios.

3. Importance of Gear Ratio Calculations

Details: Proper gear ratio selection affects acceleration, top speed, fuel economy, and engine longevity. This calculation helps optimize these factors.

4. Using the Calculator

Tips: Enter RPM (typically 1500-6500 for most vehicles), tire diameter (measure or check manufacturer specs), gear ratio (transmission gear), and axle ratio (differential). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's the 1056 constant in the formula?
A: It combines unit conversions (inches to miles, minutes to hours) and pi/12 for tire rotation calculations.

Q2: How do I measure tire diameter?
A: Measure from ground to top of tire under load, or use manufacturer specs. Formula: (Width * Aspect Ratio / 1270) + Wheel Diameter.

Q3: What's a typical axle ratio?
A: Common ratios range from 2.73 to 4.10 for passenger vehicles, with higher numbers for towing/hauling.

Q4: Does this account for tire slip or torque converter slip?
A: No, this is theoretical speed. Actual speed may be 2-5% lower due to these factors.

Q5: How does changing gear ratios affect performance?
A: Lower ratios increase top speed but reduce acceleration. Higher ratios improve acceleration but reduce top speed and may increase RPM at highway speeds.