L33T35T 4Runner

Again i HIGHLY STRESS not to go below the load index (example the "101" part of a "101S") of the factory specification. This can be very dangerous. And as everybody else mentioned, do NOT go smaller. your truck is geared for a certain size tire. Going smaller your engine will have to rev higher to maintain speed and then your MPG will just take a dump.

But do what you like, it's not my truck

L33T35T 4Runner

Ok so just a did a little reserach, a standard P225/75R15 has a load index of 102. A standard P235/70R16 has a load index of 104. So you get my 2 thumbs up there.

As for overall diameter...

P225/75R16 Long Trail T/A Tour has an overall diameter of 28.3
P235/70R16 Long Trail T/A Tour has an overall diameter of 29

So I approve. This actually will be a very good choice of size.

P225/75R16XL would be good too, overall diameter of 29.3 and load index of 106. This would keep the tire narrow to resist rolling resistance

By the way, I used a the Long Trail T/A Tour from BF Goodrich as a comparison tire because they make many different tire sized in that model, and it's a good overall tire.

Meterpig

Again, even with the smaller tire than I have right now, I am still larger than what the truck is geared for.

I am going with the LTX A/T2 because of the quality and overall rating. I know they don't make smaller tire than 225/75-but that is ok. It is better than what I have now.

I don't care much for how it "looks" as it is more or less a car for us. I care about other things now.

If I was using it for trail running, then other things would come into play given that I was in 4lo most of the time.

The 4runners are very light and are barely capable of hauling 5K-especially at altitude. I once hauled 10K with the 4runner which was, among other things, dangerous. I also noticed severe strain on the tires.

Like I said in my first post, this is considered 4runner heresy by going smaller when the whole world is going bigger.

riverrat

I totally agree with the general points here. But I wonder if 31" is the "sweet spot" for trucks like mine and the OPs that came stock with 225/75 R15 tires and were geared for that size? The OP didn't mention what engine he has (I assume the V6) but the fact that I have the 3RZ 4 cyl is a consideration in my case. I'd love to be able to experiment with 245/75 R16s for awhile, and see how my 4runner does with that size...

Texas_Ace

right, like i said, for trucks that came with 30" tires, then that stands to reason is the sweet spot vs the trucks that came with 31".

Meterpig

With 4.3 gearing, I think 225/75 might be a tad small so going just a bit bigger might work.

I have no data on this, just talking.

For the tires that I have, it would seem 4.56 would work better.