I've got the Foundry 18 x 8 inch rims on my 2015 EB Premium. If I were to upgrade to 19" or 20" rims, how much (if any) would the Outside Diameter of the tires be for each different rim? Thanks in advance.
Pigdoc

 

Ok this is easy stuff, first you go to the Mustang brochure,
http://www.ford.com/services/assets/...tang&year=2015
then you find the wheel/tire sizes
235/50/18---------255/40/19--------265/35/20
if you want the info in inches convert dividing the width say 235mm by 25.4(the number of mm in an inch), then multiply the width by the sidewall ratio so 9.252x.50=4.626, then multiply by 2, so 4.626x2=9.252, then add 9.252+18=27.252
But since I know you don't want to do all that.
235/50/18=27.252"
255/40/19=27.032"
265/35/20=27.303"
Of course actual tire size will vary due to manufacturing tolerances.
No more than about a 1/4" difference between any of them, that's why bigger wheels give a harsher ride, less side wall to absorb the road imperfections.

 

Somebody paided attention in math class.