Changing your vehicle’s tire size can offer numerous benefits, from enhanced off-road capability to improved aesthetics. However, a less discussed consequence of altering tire dimensions is its impact on your speedometer accuracy. If you’ve recently upgraded your tires and noticed your speedometer reading seems off, you’re not alone. This article will guide you through how to use a “Chg Tire Size Scan Tool” to recalibrate your speedometer and ensure accurate readings.
Why Tire Size Matters for Speedometer Accuracy
Your vehicle’s speedometer is calibrated at the factory to work with a specific stock tire size. This calibration is based on the circumference of the original tires. When your tires rotate, sensors in your vehicle track these rotations to calculate your speed and mileage. Changing to a different tire size, especially altering the tire diameter, directly affects the number of rotations per mile.
For instance, if you install taller tires, your wheels will cover more ground with each rotation than the stock tires. This means your speedometer, still calibrated for the smaller stock tires, will register a slower speed than you are actually traveling. Conversely, smaller diameter tires will cause your speedometer to read higher than your actual speed. For vehicles like the Jeep Patriot, stock 17-inch rim tire sizes might range around 215/60/r17 or 215/65/r17. Moving away from these dimensions without recalibration will lead to inaccuracies.
The Problem: Speedometer Inaccuracy After Tire Change
The most obvious symptom of speedometer inaccuracy after a tire change is a discrepancy between your speedometer reading and your actual speed. You might notice this by comparing your speedometer with GPS-based speed readings on your phone or navigation device. A small difference might seem negligible, but even a few miles per hour off can accumulate over time, affecting not just your speed readings but also your odometer.
When your speedometer underreads, meaning it shows a lower speed than you’re actually traveling, your odometer will also record fewer miles than you’ve actually driven. While this might seem minor, it can impact your vehicle’s resale value, maintenance schedules, and fuel efficiency calculations. Inaccurate speed readings can also lead to unintentional speeding, as you might believe you are driving within the speed limit when you are actually exceeding it.
Solution: Recalibrating with an OBDII Scan Tool and JScan App
Fortunately, modern vehicles equipped with electronic speedometers can be recalibrated to accommodate changes in tire size. A cost-effective and increasingly popular method for this recalibration is using an OBDII (On-Board Diagnostics II) scan tool in conjunction with a smartphone application like JScan. This combination effectively acts as a “chg tire size scan tool,” empowering you to adjust your vehicle’s computer settings to accurately reflect your new tire dimensions.
This DIY approach eliminates the need to visit a dealership or mechanic for speedometer correction, saving you both time and money. By using readily available tools and a user-friendly app, you can regain accurate speed and mileage readings after changing your tires.
Tools You’ll Need
To perform a tire size recalibration using the “chg tire size scan tool” method, you’ll need the following:
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OBDII Scanner: This Bluetooth device plugs into your vehicle’s OBDII port and communicates with your smartphone via Bluetooth. Several reliable OBDII scanners are available online. Two popular options, often recommended for their compatibility and affordability, include:
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Veepeak Bluetooth OBDII Scanner: https://www.amazon.com/Veepeak-Bluetooth-Diagnostic-Supports-Vehicles/dp/B076XVQMVS/
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Vgate Bluetooth OBDII Scanner: https://www.amazon.com/Vgate-Bluetooth-Scanner-Android-Compatible/dp/B06XGB4873
Ensure the scanner you choose is compatible with your vehicle’s make and model.
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Smartphone (Android or iPhone): You’ll need a smartphone that is compatible with the JScan application.
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JScan App: This application is specifically designed for Jeep, Chrysler, Dodge, and Ram vehicles and provides advanced diagnostic and customization options, including tire size adjustment. You can download JScan from the App Store (for iPhones) or Google Play Store (for Android phones). Note that a license purchase (approximately $20) is required to access the tire size programming feature.
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Tape Measure: A standard tape measure will be needed to accurately measure the actual diameter of your new tires.
Step-by-Step Guide: Recalibrating Your Speedometer
Once you have gathered all the necessary tools, follow these steps to recalibrate your speedometer using the “chg tire size scan tool” method:
Step 1: Connect Your OBDII Scanner
Locate the OBDII port in your vehicle. In most vehicles, it’s typically found under the dashboard on the driver’s side. Plug your OBDII scanner securely into this port.
Step 2: Set Up JScan App and License
Download and install the JScan app on your smartphone. Open the app and follow the initial setup prompts, selecting your vehicle’s make, model, and year. The app will guide you through connecting to your OBDII scanner via Bluetooth. You will be prompted to purchase a license to access advanced features like tire size correction. Complete the license purchase within the app.
Step 3: Measure Your Tire Diameter
While online tire size calculators can provide estimated diameters, it’s crucial to measure your tires directly for the most accurate recalibration. Use your tape measure to measure the diameter of your tire from the top to the bottom, ensuring you measure in a straight line through the center of the wheel. Record this measurement in inches.
Step 4: Enter New Tire Size in JScan
Within the JScan app, navigate to the “Adaptations” or “Configuration” section. Look for the “Tire Size” or “Speedometer Calibration” setting. The app might display your current (incorrect) tire size setting. Enter the tire diameter measurement you obtained in Step 3 into the app. Follow the app’s instructions to write the new tire size setting to your vehicle’s computer. This process may take a minute or two, so be patient and do not interrupt the process by closing the app or disconnecting the scanner.
Step 5: Verify Speedometer Accuracy
After successfully writing the new tire size, it’s essential to verify the accuracy of your speedometer. Use a GPS-based speedometer app on your smartphone or a standalone GPS device. Drive at a steady speed and compare your speedometer reading to the GPS speed. Ideally, they should now be very close or identical. You can also use a “Car Scanner ELM OBD2” app (recommended in some OBDII scanner instructions) to view sensor data and further confirm speedometer accuracy.
Important Considerations and Troubleshooting
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Connection Issues: Occasionally, you might encounter Bluetooth connection issues between your smartphone and the OBDII scanner. If this happens, try closing and reopening the JScan app, disconnecting and reconnecting the OBDII scanner, or ensuring your vehicle’s ignition is switched to the “ON” position (engine can be off or on).
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Processing Time: When submitting tire size changes in JScan, allow sufficient time for the change to process. It may take up to two minutes. Avoid interrupting the process.
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Warning Lights: In rare cases, users have reported temporary warning lights, such as ABS lights, appearing after making changes with JScan. These are often temporary glitches and disappear after restarting the vehicle. However, it’s crucial to exercise caution and only change settings you are confident about. Incorrect settings can potentially affect other vehicle systems.
Benefits of Using a Scan Tool for Tire Size Correction
Utilizing a “chg tire size scan tool” like an OBDII scanner and JScan app offers several advantages:
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DIY Convenience: You can perform the speedometer recalibration yourself at home, eliminating the need for professional assistance.
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Cost-Effectiveness: The cost of an OBDII scanner and JScan license is significantly less expensive than dealership or mechanic service charges for speedometer correction.
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Accuracy: When done correctly, this method provides accurate speedometer and odometer readings, ensuring your vehicle’s measurements are reliable.
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Versatility: JScan and similar apps often offer other diagnostic and customization features beyond tire size correction, providing added value.
Conclusion
Correcting your speedometer after a tire size change is crucial for maintaining accurate speed and mileage readings, and ensuring safe driving. Using a “chg tire size scan tool,” specifically an OBDII scanner and the JScan app, provides a straightforward, affordable, and effective DIY solution. By following the steps outlined in this guide, you can easily recalibrate your speedometer and enjoy the benefits of your new tires with confidence and accuracy.
