1. What is the Final Drive Ratio?

The final drive ratio is the gear reduction in the vehicle's drivetrain that multiplies the torque from the transmission to the wheels. The effective ratio accounts for tire size and pressure through the tire factor.

2. How Does the Calculator Work?

The calculator uses the effective ratio formula:

Where:

• \( Ratio \) — The nominal gear ratio (dimensionless)
• \( Tire Factor \) — Adjustment factor for tire size and pressure (dimensionless)

Explanation: The tire factor accounts for how changes in tire diameter (affected by size and pressure) alter the effective gear ratio.

3. Importance of Tire Factor

Details: The tire factor is crucial because larger tires effectively reduce the final drive ratio (making it numerically lower), while smaller tires increase it. Tire pressure also affects the rolling diameter slightly.

4. Using the Calculator

Tips: Enter the nominal gear ratio and the calculated tire factor (typically between 0.9 and 1.1 for most applications). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: How do I determine the tire factor?
A: The tire factor is calculated as (original tire diameter)/(new tire diameter). Measure or look up manufacturer specs for diameters.

Q2: How much does tire pressure affect the ratio?
A: Pressure has a minor effect (typically <1% change in effective ratio) unless pressure changes are extreme.

Q3: What's a typical final drive ratio?
A: Passenger cars typically range from 2.5:1 to 4.5:1, while trucks may have ratios up to 6:1 or higher.

Q4: Why is effective ratio important?
A: It determines actual torque multiplication and affects acceleration, fuel economy, and top speed.

Q5: Does this account for tire wear?
A: No, this calculator assumes new tire diameters. Significant tread wear would slightly increase the effective ratio.