Tires: tires for larger rims, rear tire size, cadillac sts

Question
Hello my name is AnTonio I have a 2005 Cadillac STS it currently has 17"x7.5 rims front tire size 235/50/17 rear tire size 255/45/17 I was wanting to put 20"x8 rims what would be the best tire sizes for this set up and do I need to keep the tire size split or can I put the same all round as far as the height goes? THANK YOU

Answer
AnTonio,

Both Tire Rack and Discount Tire have on line tire upsize programs.

http://www.tirerack.com/

http://www.discounttire.com/dtcs/home.do

Follow those for the best advice available.  They will tell you about the staggered fitement, but I think the car is supposed to have the stagger continued for handling reasons - but both of them will tell you the answer.