Calculate Gear Ratio With Tire Size

Effective Gear Ratio Formula:

\[ \text{Effective\_GR} = \text{GR} \times \left( \frac{\text{New\_Tire\_Diam}}{\text{Old\_Tire\_Diam}} \right) \]

Effective Gear Ratio:

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1. What is Effective Gear Ratio?

The effective gear ratio calculation determines how changing tire size affects your vehicle's final drive ratio. When you install larger or smaller tires, it changes the effective gear ratio, which impacts acceleration, fuel economy, and speedometer accuracy.

2. How Does the Calculator Work?

The calculator uses the effective gear ratio formula:

\[ \text{Effective\_GR} = \text{GR} \times \left( \frac{\text{New\_Tire\_Diam}}{\text{Old\_Tire\_Diam}} \right) \]

Where:

\( \text{GR} \) — Original gear ratio (unitless)
\( \text{New\_Tire\_Diam} \) — New tire diameter in inches
\( \text{Old\_Tire\_Diam} \) — Original tire diameter in inches

Explanation: The formula calculates how much your effective gear ratio changes when you install different sized tires. Larger tires effectively lower your gear ratio, while smaller tires effectively raise it.

3. Importance of Gear Ratio Calculation

Details: Understanding effective gear ratio is crucial for maintaining proper vehicle performance after tire changes. It affects acceleration, towing capacity, fuel efficiency, and ensures your speedometer remains accurate.

4. Using the Calculator

Tips: Enter your original gear ratio, the diameter of your old tires, and the diameter of your new tires. All values must be positive numbers. Tire diameter should be measured in inches for accurate results.

5. Frequently Asked Questions (FAQ)

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

Q2: How do I measure tire diameter?
A: Measure from the ground to the top of the tire while properly inflated, or calculate using tire size markings (e.g., 275/65R18).

Q3: What is a typical gear ratio range?
A: Most vehicles have gear ratios between 2.73:1 and 4.10:1, with performance and towing vehicles often having higher ratios.

Q4: How does this affect my speedometer?
A: Changing tire size without adjusting the speedometer calibration will cause it to read inaccurately. Larger tires make it read slower than actual speed.

Q5: Should I regear after changing tire size?
A: For significant tire size changes (more than 2 inches), regearing may be necessary to maintain optimal performance and fuel economy.