If you have replaced your vehicle's speedometer or odometer, Road Trip can be configured to use your new odometer while preserving your existing fuel, expense, and trip data.
When you replace your vehicle's odometer, make a note of the last odometer reading from the original odometer, as well as the initial odometer reading from your new odometer.
In Road Trip, select Vehicle Info > Tools > Replace Odometer.
Enter the last reading from your old odometer, as well as the initial reading from your new odometer. Your new odometer can be in either miles or km and Road Trip will perform the necessary conversion.
Finally, select Convert to convert your data to the new odometer. This operation will create a new vehicle in Road Trip without affect any of your existing data. The converted vehicle will have "(New)" prepended to the vehicle name.
You can review the data in the new vehicle to ensure it now matches your vehicle's current odometer. Once you're satisfied with the conversion you can delete or archive the original vehicle.
Note that the converted vehicle may now contain negative odometer values. This is normal and expected if your new odometer has a lower value than your original odometer.