Check the panel on the drivers side door of your xj ,both of mine list 215/75r15 as the stock tire sizethat should only be slightly smaller then 225's .If anyone has 225/75r15's on they could tell us what the proper rpms are for 60 and 70mph.My 94 speedo is still setup for the stock tires,my 2001 has been set for my 31x10.50's and runs 2200-2250 at 70mph.