Tires: How much width can I loose on my Ford factory r18 rims?

Question
Currently I have a 2006 F150 with 275/65/R18's factory ford rims. I was wondering if I buy 265's will they beable to be put on these rims without issue? I'm sure you've been asked this, I was trying to find an answer.
Thanks,
Joe

Answer
Joe,

First, there are other numbers in the tire size besides 265 (and obviously 18) - and they affect the answer.  In fact, there are so many different answers depending on what the middle number is that I really can't answer your question.

Plus, it is never a good idea to go down in load carrying capacity and that sounds like what you are trying to do.  

You didn't indicate what you are trying to accomplish  - and I've seen people try to use different sized tires only to find out their idea was false.

So post back with the middle number and I'll try to answer your question.  Plus let me know WHY you are thinking about the change.