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Final Drive Ratio Equation:
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The final drive ratio is the gear reduction in the vehicle's drivetrain that converts the rotational speed of the transmission output shaft to the rotational speed of the wheels. It's a crucial factor in determining a vehicle's acceleration, top speed, and fuel efficiency.
The calculator uses the final drive ratio equation:
Where:
Explanation: The equation calculates how many times the driveshaft rotates for each rotation of the wheels, accounting for tire size and vehicle speed.
Details: The final drive ratio affects vehicle performance characteristics. Lower ratios provide better fuel economy and higher top speed, while higher ratios improve acceleration and towing capacity.
Tips: Enter RPM (engine speed), tire circumference in inches, and vehicle speed in mph. All values must be positive numbers. For accurate results, measure tire circumference when properly inflated.
Q1: How do I measure tire circumference?
A: Measure from the ground to the center of the axle (radius), multiply by 2 to get diameter, then multiply by π (3.1416). Or roll the tire one revolution and measure the distance traveled.
Q2: What's a typical final drive ratio?
A: Passenger cars typically range from 2.5:1 to 4.5:1. Performance cars may have higher ratios (4.0:1 to 5.0:1) while economy cars have lower ratios.
Q3: How does tire size affect the ratio?
A: Larger tires effectively lower the final drive ratio (fewer driveshaft rotations per wheel rotation), while smaller tires increase it.
Q4: Can I use this for different gear positions?
A: This calculates overall final drive ratio. For gear-specific calculations, you'd need to multiply by the transmission gear ratio.
Q5: Why is 336 the constant?
A: The 336 combines unit conversions: (5280 ft/mile × 12 in/ft) ÷ (60 min/hour × π × 2) ≈ 336.