225/45-R17 tires are 0.01 inches (0.2 mm) smaller in diameter than 195/65-R15 tires and the speedometer difference is 0.1%.
205/55-R16 tires are 0.21 inches (5.3 mm) smaller in diameter than 225/40-R18 tires and the speedometer difference is 0.9%.
I track Miatas and for best performance use 225 width tires on 9" wheels. But, the tires are the most important component by far. A race 225 width tire on a 6" wheel will perform better than a street 225 width tire on 7" or 8" or 9" wheel, or a street 245 width tire for that matter (if the car has enough horsepower).
215/55-R17 tires are 1.69 inches (43 mm) larger in diameter than 215/45-R17 tires and the speedometer difference is 6.5%.
205/70-R14 tires are 0.55 inches (14 mm) smaller in diameter than 215/70-R14 tires and the speedometer difference is 2.1%.
. 63 444 120 281 287 258 91 370
difference between 205 and 225 tires
