My on-order F350 SRW is coming with 275/70R18 AT tires. Could be either Michelins or Goodyear Wrangler, neither of which are rated very good for snow.
I am considering swapping tires before pickup for that reason, and also to gain some load capacity by going with 285/75R18 Wrangler Duratrac. These are 35" tires.
I would then sell the stock tires on craigslist or locally. The dealership has a fair price for those tires if they don't overdue the installation charges. Could get them at Discount Tire for the same price and include install and rotations.
So, a couple questions. It would seem that it would be smart to switch out all 5 tires.
What kind if rim does the spare come on?
And will that 35" tire fit in the spare tire compartment?

 

On my Lariat all five tires are the same size as you listed. The spare wheel is a different type (steel?) than the other four. I think I've read that there is room for a slightly larger tire.

Unless you planned to include the spare tire in your tire rotations I wouldn't replace it.

 

 

 

No reason to swap for seasons is for sure. The DT's are good tires all year round. That's what I have on my work truck.

Rotate often, every 10,000 at least. Miss a rotation, they're toast and will have dismal wear mileage. I'm on my 4th set. Also note, they'll be loose and very wiggly the 1st 5000 miles until they dry out somewhat. Keep your pressures maxed out during that time. (88 psi for me)

 

All the 18" AT tires I've seen have been the Goodyear Wranglers.

I had a set and didn't like them on wet roads so I replaced them with 295/70R18 Nitto Ridge Grapplers. So yeah I would replace them.
The spare is on a steel wheel with a Goodyear Wrangler.

Getting a matching sized spare makes sense if you're out in the boonies using 4x4, and if you pick up a matching wheel with tpms sensor you could get the money out of it with 5 wheel rotations.

295s fit under the bed so 285s should.