Do you have 18" rims for them to be mounted to? Stock CX-5 rims are either 17" or 19". A 235/65R18 is 4.5% larger in diameter then the stock tires of either size so your speedo will be off quite a bit using those. 245/55R18 would be a much better size if the wheels you plan on using are at least 8" wide.
