This is for a 4th gen.

Been searching on here and using the tire calculators and it seems that if I want to keep the speedometer as accurate as possible I would go to a 235/40/18? Also, it seems, according to the tire calculators, that I would use a 235/40/18 for both the 8.5" as well as the 8" wheel. Is this correct?

Also, for my own personal knowledge, I was reading the tirerack.com article describing what tire sizes mean and the article mentions that the 235 is a millimeter measurement from the outside tire wall to the inside tire wall. To convert this measurement to inches is to divide the number by 25.4, which is the amount of millimeters in an inch. My question is this: my stock tires are 215/55/16. According to tirerack.com and their math, that is 8.46." This makes no sense to me because the wheel is only 6.5" wide and the tire conforms to that wheel and is very skinny. Yet a 235 wheel, which is only 9.25" will fit and conform to a 8" wheel? What am I missing here?

 

That is the tire width, not the wheel width. The tires you speak of (235) are 9.25" wide, and you are wrapping them around an 8" or 8.5" wheel.

Personally, I like the way 245-40 18"s look on an 8" wide wheel an an A32 chassis.

Also, for better handling, you want a wheel that is about 90% of your tire width. But of course iIt all depends on the tire though. Also, keep this term in mind : Aspect Ratio.