calculate it dude

205 is the tread width 45 is tire wall's percentage in respect to the treadwidth. once you find that number divide by 25.4 to put it in inches. multiply the sidewall by two and add the diameter of the rim (to get total diamter) multiply by pi and you get your total circumference

do that for your stock wheels and the ones you are looking at. 40 is small 45 is slightly larger in this case