My 2017 originally came on 195/45/16s. The speedo was more or less dead on accurate with GPS.

A couple years ago I put on 17x7s with 205/40/17s. Ever since my speedometer has read lower than actual, not ideal.

70 on my speedometer is 72 mph GPS. When I was able to top the car out, the speedo said 133, and GPS 138!

I have gone to the ends of the earth to find a way to change this calibration, and that took me to AlfaOBD. I have found at least two ways in the body computer.
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Not sure if that will be readable for you, but there is both a speedometer tolerance and a tire size function.

The problem is proxi aligning after, I don't have the factory radio in. I have an Alpine with the Maestro RR for CAN communication.

Has anybody successfully used these option to fix their speedo? Or can test it?