Calculate Gear Ratio From RPM And Speed

Gear Ratio Formula:

\[ \text{Gear Ratio} = \frac{RPM \times \text{Tire Circumference} \times 60}{\text{Speed} \times \text{Final Drive} \times 63360} \]

RPM:

revolutions per minute

Tire Circumference:

inches

Speed:

mph

Final Drive Ratio:

unitless

Gear Ratio:

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1. What is Gear Ratio?

The gear ratio is the ratio of the number of rotations a drive gear must make to spin a driven gear once. In automotive terms, it represents how many times the engine turns for each revolution of the wheels.

2. How Does the Calculator Work?

The calculator uses the gear ratio formula:

\[ \text{Gear Ratio} = \frac{RPM \times \text{Tire Circumference} \times 60}{\text{Speed} \times \text{Final Drive} \times 63360} \]

Where:

\( RPM \) — Engine revolutions per minute
\( \text{Tire Circumference} \) — Distance traveled in one tire revolution (inches)
\( \text{Speed} \) — Vehicle speed (miles per hour)
\( \text{Final Drive} \) — Final drive ratio (unitless)
60 — Conversion factor (minutes to hours)
63360 — Conversion factor (inches to miles)

Explanation: The formula calculates how many times the engine turns for each revolution of the wheels at a given speed.

3. Importance of Gear Ratio Calculation

Details: Gear ratio affects vehicle performance, fuel efficiency, and engine longevity. Proper gear ratio selection ensures optimal power delivery across different driving conditions.

4. Using the Calculator

Tips: Enter RPM (engine speed), tire circumference in inches, vehicle speed in mph, and final drive ratio. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: How do I measure tire circumference?
A: Measure from ground to wheel center (radius), multiply by 2 for diameter, then multiply by π (3.1416). Or roll the tire one revolution and measure distance traveled.

Q2: What is a typical final drive ratio?
A: Passenger cars typically range from 2.5:1 to 4.5:1, while trucks may have ratios from 3.5:1 to 6.5:1.

Q3: Why does gear ratio matter?
A: Lower ratios provide better acceleration but lower top speed, while higher ratios improve fuel efficiency at cruising speeds.

Q4: How does gear ratio affect RPM?
A: At a given speed, a lower gear ratio means higher engine RPM, while a higher gear ratio means lower RPM.

Q5: Can I use this for different transmission gears?
A: This calculates overall gear ratio. For specific transmission gears, multiply this result by the transmission gear ratio.