1. What is the Final Drive Gear Ratio Calculator?

The Final Drive Gear Ratio Calculator helps determine the adjusted gear ratio when changing tire sizes. It calculates how your vehicle's performance characteristics will change with different tire diameters.

2. How Does the Calculator Work?

The calculator uses the following formula:

Where:

• \( \text{Ratio} \) — Original gear ratio (dimensionless)
• \( \text{New Tire} \) — Diameter of new tires (inches)
• \( \text{Old Tire} \) — Diameter of original tires (inches)

Explanation: The formula accounts for the change in effective gear ratio caused by different tire diameters. Larger tires effectively decrease your final drive ratio, while smaller tires increase it.

3. Importance of Ratio Adjustment

Details: Correctly calculating the adjusted ratio is crucial for maintaining proper vehicle performance, fuel efficiency, and speedometer accuracy when changing tire sizes.

4. Using the Calculator

Tips: Enter your original gear ratio, old tire diameter, and new tire diameter in inches. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why does tire size affect gear ratio?
A: Larger tires cover more ground per rotation, effectively making your final drive ratio numerically lower, while smaller tires do the opposite.

Q2: How do I measure tire diameter?
A: You can calculate tire diameter using the sidewall markings (e.g., 265/75R16) or measure the actual mounted diameter with a tape measure.

Q3: What's a typical gear ratio range?
A: Most passenger vehicles have final drive ratios between 2.5:1 and 4.5:1, while trucks may have ratios up to 6:1.

Q4: How does this affect performance?
A: Larger tires (lower effective ratio) reduce acceleration but may improve fuel economy at highway speeds. Smaller tires increase acceleration but reduce top speed potential.

Q5: Should I adjust my speedometer after changing tire sizes?
A: Yes, significant tire size changes require speedometer recalibration to maintain accuracy.