Wheel size has nothing to do with the speedometer calibration. That depends completely on tire outer diameter. The stock 19" tires are 255/45R19, not 235.
This thread is about using the Model 3 18" Aero wheels, which would optimally have a 255/50R18 tire to match the OE tires, but that size isn't available with any real selection of tires. The closest sizes that do have tire choices are 245/50R18 or 245/55R18.
Sorry wasn’t trying to hijack this thread but since it was about 18” wheels and I’m looking at something similar wanted to get some input.
Also, I was looking at 235 because of the 18x8.5" wheel and thought that would fit it.