[MeteorGray]

You're on the right track for coping with poor roads and their potholes:

---the bigger the diameter, the better a wheel can span the gap in potholes

---the smaller the metal wheel for any given overall metal-wheel-and-tire-combo diameter, the more air-and-rubber "cushioning" effect a tire can provide for the combo.

And about the speedometer: IMHO the best solution is the ScanGauge. It is easy to change the gauge's calibrations to the exact speed of the car regardless of its wheel diameter, and it'd think it's a lot cheaper and more convenient than trying to get the car's computer reprogrammed.

I no longer look at my Mazda's speedometer and depend entirely on my ScanGauge. Not only is it more accurate especially since I've got larger-than-OEM wheels and I've adjusted it to them, it's more precise because it's digital and I can read it a lot better than the factory analog speedometer.

Besides, the ScanGauge has allowed me to achieve consistently better fuel economy by showing me how to hone my operating skills relative to speed, hills, wind, and etc.