Heritage Blue 4Runner SR5 — The Start of My Build (Please Help!)

[neilkansal]

That is correct logic, you'll also put less strain on your engine, suspension components, MPG, etc.

If you don't plan on lifting/upgrading suspension but adding a good bit of weight I think 275's are your optimal choice. The more weight the more your suspension compresses = rub.

If I was keeping my build as is I'd probably be running 275's as well. But full width front and rear bumpers are too much weight to be abusing stock suspension off road.

I think you’ve sold me. A real beefy looking 275 should do the trick paired with a 1.25in spacer

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[MikeD]

I think you’ve sold me. A real beefy looking 275 should do the trick paired with a 1.25in spacer

With 275s on your stock 17 +55 offset wheels you will probably be OK with subtracting 31.75 mm (1.25") to effectively go down to +23 mm offset.
I've avoided commenting earlier because I don't really know how the TRD OR (my vehicle) suspension differs from the SR5. The tire size difference (265/70/18 vs 17) accounts for 1/2" of the 1" difference in ground clearance so assumedly it is strut length and suspension geometry that accounts for the rest - but I really don't know about SR5 fitment. However, I can say this:
On a TRD OR, 285/70R18 tires on TRD PRO +20 offset wheels rubs the rear fender when fully articulated (i.e., on a very rocky trail). I switched to the TRD Flat Black +45 offset wheel to avoid this in the future. (Note: if I had a PRO or TH the extended fenders would not have rubbed - which is consistent with them having +20 offset wheels)
Your 275/70R17s at +23 effective offset will almost certainly NOT have this problem but I wanted to offer the caution since you mentioned the spacer (and I see others on this forum describing setups with spacers that I KNOW will rub the fender at full articulation).
You might even be OK with the 285s given the inch smaller diameter but ... offset matters!
Here is my test to convince myself that I had fixed the rub by moving to the +45 offset wheels (I couldn't quite get this set up to full articulation but the angles and apparent clearance convinced me I had fixed the problem):

 

[neilkansal]

With 275s on your stock 17 +55 offset wheels you will probably be OK with subtracting 31.75 mm (1.25") to effectively go down to +23 mm offset.
I've avoided commenting earlier because I don't really know how the TRD OR (my vehicle) suspension differs from the SR5. The tire size difference (265/70/18 vs 17) accounts for 1/2" of the 1" difference in ground clearance so assumedly it is strut length and suspension geometry that accounts for the rest - but I really don't know about SR5 fitment. However, I can say this:
On a TRD OR, 285/70R18 tires on TRD PRO +20 offset wheels rubs the rear fender when fully articulated (i.e., on a very rocky trail). I switched to the TRD Flat Black +45 offset wheel to avoid this in the future. (Note: if I had a PRO or TH the extended fenders would not have rubbed - which is consistent with them having +20 offset wheels)
Your 275/70R17s at +23 effective offset will almost certainly NOT have this problem but I wanted to offer the caution since you mentioned the spacer (and I see others on this forum describing setups with spacers that I KNOW will rub the fender at full articulation).
You might even be OK with the 285s given the inch smaller diameter but ... offset matters!
Here is my test to convince myself that I had fixed the rub by moving to the +45 offset wheels (I couldn't quite get this set up to full articulation but the angles and apparent clearance convinced me I had fixed the problem):

Thanks Mike, that’s a really great explanation and I appreciate it! So what I’m hearing is id probably be okay with 285s with a 1.25in spacer…

 

[MikeD]

Thanks Mike, that’s a really great explanation and I appreciate it! So what I’m hearing is id probably be okay with 285s with a 1.25in spacer…

That is my guess.
The issue of fitting 285s on your 7" wide wheels (when the tire manufacturers give a 7.5"-9" "approved rim width") is a separate matter of which I have no experience. (Am guessing it would work but might not be worth the risk.) My TRD ORP OEM wheels were 7.5". TRD Flat Black are 8". TRD PRO are 8.5". (All 18" dia.)
I'll note, however, that the narrower wheel further diminishes the poke - and the possibility of rear fender rub at full articulation. so there is that....

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