The speedo reads over so at 30 it would read 35 so it shouldn't be the cause of a speeding fine. Happy sunny motoring
But it's also adding an inflated number of miles at 8.5% per mile. At least if you were to go a constant 30 mph. I may stay the same all through your mph range at a flat percentage fast.
I know it's nice to have a cushion "safety" factor built in, but not at an 8.5% surcharge in miles accrued.
I would get the speed calibrated and some of the calibration modules work well. Also they make a GPS module that you can convert to that sends out pulse to the speedo.
