Tires: 255/70/18 on 9 inch rim, steel rims, rim width

Question
I have a new tundra with 255/70/18 tires on 18x8 inch steel rims. I want to upgrade to a rim that only comes in 18x9 inch. Can I safely use these tires on the new rims?

Answer
Terry,

The allowable rim width range for a P255/70R18 is 6 1/2" to 8 1/2".

So, no, this is not a good fitment.

But if you change the tire size to P265/65R18, that will fit on the rim and still have the same load carrying capacity.  

The only question will be - Will it fit on your vehicle?  And I'm sorry, but I can't tell you the answer to that question, but the folks that are selling you the rim should be able to - unless they really aren't doing the professional job they ought to.