What is your Gear and Speed Ratio?

Semi-Truck Gear Ratio & Speed Calculator

Please note these calculators are provided for informational purposes only and unrelated to Drivewyze and its software products.

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Understanding your semi-truck’s speed capability is essential for safe driving, especially during long journeys on highways. Our easy-to-use Speed Calculator assists truck owners and operators in estimating their speed based on Ring & Pinion Gear Ratio, RPM, Tire Diameter (mm), and Overdrive Gear Ratio. By inputting these parameters, our calculator swiftly computes the truck’s speed in MPH.

Calculate Your Truck’s Speed

Formula Used

Speed (MPH) = (RPM × Tire Diameter (inches) × Overdrive Gear Ratio) / (Gear Ratio × 336)


In this formula:
  • RPM is the revolutions per minute of the engine.
  • Tire Diameter is the diameter of the tire in mm.
  • Overdrive Gear Ratio and Gear Ratio affect how the engine’s power is translated to movement.

Speed & Gear Ratio Calculation Example

Suppose a truck has the following specifications:

  • Ring & Pinion Gear Ratio: 3.55
  • RPM: 2500
  • Tire Diameter: 1000mm (39.37 inches)
  • Overdrive Gear Ratio: 0.75

Using the formula, the calculated speed would be approximately 66.15 MPH.

How Gear Ratios Affect Your Truck’s Speed

Gear ratios play a significant role in determining how the engine’s power is transferred to the wheels. A lower gear ratio can provide more power but less speed, while a higher gear ratio can offer greater speed but less power.

Further, your truck’s gear ratio has a major impact on its fuel efficiency and performance. This is especially true when considering the impact of various gears, like the difference between 1st gear, 5th gear, 12th gear, and more. For example, a lower gear ratio (i.e., 1st or 2nd gear) can give your truck more torque and make it easier to haul heavier loads or drive in the mountains.

On the other hand, higher gears allow for greater speeds and require less effort. Here are additional ways to enhance the average vehicle speed of your fleet:

  • Use an RPM calculator or learn how the transmission gear ratio interacts with torque converters and differential ratios
  • Modify your truck with aftermarket sprockets or adjust the number of teeth in the gears
  • Fine tune your truck’s differential and final drive ratio

Frequently asked questions (FAQs)

Why is knowing my truck’s speed important?

Understanding your truck’s speed potential is essential for several reasons. It helps you plan routes more effectively, ensuring that you adhere to speed limits and maintain safe driving conditions. Additionally, knowing your speed can help you meet delivery deadlines, optimize fuel efficiency, and avoid costly fines or accidents, ultimately leading to smoother and more profitable journeys.

Given ideal conditions, a truck with a gear ratio closer to 3.23 is likely to achieve greater fuel efficiency and even higher maximum speeds. While truck’s with gear ratios closer to 3.42 might be slightly less fuel efficient, but will have a quicker acceleration alongside more torque at lower RPMs.

Yes, the tire diameter directly influences the distance a truck can travel in one tire revolution. Larger tires will cover more ground per revolution, potentially increasing the speed if all other variables remain constant.

This calculator provides an estimate based on the input values provided. Real-world factors, such as truck load, terrain, and engine efficiency, can influence the actual speed.

We offer a number of calculators for the trucking industry, including:

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