I have an '07 X5 4.8 CPO. The original window sticker says I have the "ZSP" Sports Package w/ 19" wheels - a $3,600 option at the time. My rear tires are bald and need replacing. When I look online for sizing at tire stores, their sites universally tell me that the X5 4.8 w/ sports package has larger tires on the rear versus the front. Yet, all my tires are sized the same Michelin Latitude Tour HP ZP(255 50 19).

Any thoughts on what I should get?