MPH changes?
 

so if i go from 17X9's to 18x(anything) am i going to have to get the speedometer re-calibrated? some people have mentioned it to me that changing tire sizes could affect the speedometer... i didn't really know so i thought i'd ask...

depends on if u change ur tire size. the speed changes from teh outside diameter, (tire) not the inside diameter (wheel) soo if u go from running stock 16x8's? with stock tires on it to an 18 w/low profiles on it, ur speedo. shouldn't change much at all if the outside size is about the same

Yup...it is all about the tire and wheel height. As long as it stays equal, the speedo will be the same.