STEP 1 – Plug up your RTD Interface and your laptop to your vehicle.
NOTE: You will be using VCM Scanner BETA (not the RTD Flasher or VCM Editor) for this procedure, so open up that too.
*If you have not downloaded the VCM Scanner software, you can do so by clicking here.
STEP 2 – Connect to the vehicle by clicking on the Connect to Vehicle icon.
STEP 3 – Click the Vehicle Controls & Special Functions icon.
NOTE: If you get an empty window and do not have the option for the adjustment, click here for instructions. Complete that process, then continue on from here.
STEP 4 – Inside that box click on the Speedometer tab and select Speedometer Adjustment.
STEP 5 – The software will show the vehicle's current stored axle ratio. Enter your actual axle ratio here. If the displayed axle ratio matches your actual axle ratio, reenter the value in the box as it is required to enter a value in this field to move to the next step in the process. Input the correct value and click “OK”.
STEP 6 – Enter your tire size data here. We have included the Revs/Mile value for the tire size that you listed on your tune form. Please ONLY use this value. DO NOT use values from online calculators or tire manufacturers websites. If you listed more than one tire size on your tune form, we have included the Revs/Mile value for both tires (does not apply to forced induction tunes), and you will need to enter the Revs/Mile value that corresponds to the tires you have or plan to install and you must load the corresponding tune to go with those tires.
Revs Per Mile Example
STEP 7 – After calibrating your speedometer and installing your tune, you MUST verify the speedometer is accurate. You can use a phone app like Waze or a performance monitoring device like a Dragy or any other reliable method to measure GPS speed.
- The easiest way to verify speedometer accuracy is by reaching a relatively high and stable speed on the highway, as any error in the speedometer calibration will increase as vehicle speed increases. Using higher speeds will make it easier to see any error.
- We recommend testing at speeds between 80-100 mph IF you can do so safely.
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If your speedometer is more than +/- 1 mph off between 80-100 mph, reply to the email that was sent with your tune.
- Include the error you measured - For example Speedo=100 mph and GPS=105 mph. We need to know both the speedometer speed and GPS speed. Please do not reply and say "My speedo is 7 mph off" as that is not sufficient information to help you.
- Once you provide the necessary info, our calibrators will help you find the cause of the error and help you correct it.
If there are any other prompts, just click “OK” on them. That’s it. Done!
