Optimizing Speed Reading for Custom Tire Sizes and Gear Ratios – Hypertech, Inc.

We will be closed Monday, May 27th in observance of Memorial Day

Optimizing Speed Reading for Custom Tire Sizes and Gear Ratios

Speedometer Calibration Necessities for Custom Tire and Gear Ratios

Your vehicle's speedometer comes calibrated to the tire size/rear gear ratio that was installed on the vehicle by the manufacturer. Changing either the tire size or the rear gear ratio that was installed by the manufacturer will more than likely mean an inaccurate speed reading. And remember…An accurate speed reading is required by law.

Solutions Offered by Hypertech


Hypertech offers two options to correct an inaccurate speed reading from a larger tire size or different rear gear ratio. The Speedometer Calibrator® and the In-Line Speedometer Calibrator® Module. Doing a Year/Make/Model search at www.hypertech.com for your vehicle will show you which of these products is available for your vehicle.

Installation and Usage

Installation and using both products is quick and easy. The Speedometer Calibrator has a 4.3” color screen with user-friendly navigation for simple installation/feature changes. It also lets you read/display/clear diagnostic trouble codes, along with a few other application-specific performance features. Our In-Line Speedometer Calibrator Module is perfect for vehicles with computers that don’t allow for tire size/rear gear correction or tire sizes/rear gear ratios that are outside the range of programmers. The In-Line Speedometer Calibrator Module installs behind the instrument cluster using factory-style connectors. And depending on the application, the Speedometer Calibrator and In-Line Speedometer Calibrator Module is 50-State legal.

Testing Your Speedometer’s Accuracy

Testing the accuracy of the speedometer after installation is a simple matter of using a GPS system. That can be either factory-installed or aftermarket. Have someone help you so that you can keep your eyes focused on the road while driving to test your recalibrated speed reading. You call out the numbers of your speed while looking at the vehicle's speedometer, and your friend watches the GPS system, which will also display the vehicle’s speed on the screen.