Factory equipment size should be located on a sticker on the door frame or side of the driver's doorjamb. Any local tire shop will be able to give you the correct size also. Not knowing if you have different wheels, I can tell you my '92 Cherokee Sport will take a 235-75R15 on the small side.
why not just put the same size tire on that you are taking off? seems pretty simple
Search Jeep Grand Cherokee Questions
Jeep Grand Cherokee Experts
Related Models For Sale
Used Cars For Sale