1. What is Effective Gear Ratio?

The effective gear ratio is the actual ratio that accounts for both the rear axle ratio and the overdrive transmission ratio. It represents the final drive ratio when the overdrive is engaged.

2. How Does the Calculator Work?

The calculator uses the effective ratio formula:

Where:

• \( \text{Rear Ratio} \) — The ratio of the rear differential (e.g., 3.73, 4.10)
• \( \text{Overdrive Ratio} \) — The ratio of the overdrive gear (typically 0.70-0.80)

Explanation: The overdrive ratio reduces the effective rear ratio, resulting in lower engine RPM at highway speeds.

3. Importance of Effective Ratio

Details: Knowing the effective ratio helps in selecting the right gear combination for optimal performance and fuel economy, especially for highway driving.

4. Using the Calculator

Tips: Enter your vehicle's rear axle ratio and overdrive ratio (typically found in your vehicle's specifications). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical overdrive ratio?
A: Most overdrive ratios range between 0.70 and 0.80, meaning the output shaft turns 70-80% as fast as the input shaft.

Q2: How does effective ratio affect performance?
A: A lower effective ratio (numerically smaller) reduces engine RPM at cruising speeds, improving fuel economy but may reduce acceleration.

Q3: Where can I find my vehicle's rear ratio?
A: Check your owner's manual, vehicle specifications, or look for a tag on the rear differential. Some vehicles have it listed in the glove box or door jamb.

Q4: What's the difference between overdrive and final drive ratio?
A: The final drive ratio is the rear axle ratio, while overdrive is an additional gear reduction in the transmission. The effective ratio combines both.

Q5: Can I use this for non-overdrive transmissions?
A: For direct drive (1:1 ratio), simply use 1.0 as the overdrive ratio, which will give you the rear ratio as the effective ratio.