I just bought a 2007 XLT Screw 4x4 and the tires that are on it are 265/70/17.
When I looked at the tire data tag on the door it says the tires should be 275/65/18. I looked up my truck on tirerack.com and it says I have two possible OEM sizes 255/70-17 or 275/65-18. When i measured the wheel with the tire on I got about 18 1/2" outside to outside. Measured just inside the rim lip I got 18". I know this going to sound stupid but is it possible to put a 17 tire on an 18 wheel?

 

No. They are 17s. At some point someone traded or sold the 18s for the 17s. Happens often. 17 inch tires are cheaper and u can't really notice an inch difference.