I saw a VX that has 20x9 KMC Thunder wheels and Falkien tires. The owner said the tires are the same diameter of the orginal wheels so his speedometer reads correctly.

I'm no tire expert and was wondering how this can be. So if I were to get 20x9 wheels, what kind of tires would I need to get so the diameter is still the same as the orginal? I love the look of 20" wheels, but do not want my speedometer to be incorrect.

I wish I understood this stuff better