For some reason it seems 285/75 tires are far and away the most common tire people aspire to put on their rigs regardless of an individual's actual driving habits, conditions, etc. This completely confounds me. Cars are not an inexpensive hobby, and it seems silly to waste money like that (not only on the tires themselves, but the related repairs and modifications that result). The subject of 255s/285s subject has come up in a number of threads here lately, and I feel most people are basing their decisions on these sorts of things based on aesthetics, W-esque feelings, and "what Bobby-Joe did" rather than anything all that objective or substantial... Hopefully it's for lack of information rather than such poor decision making.
For starters, read
this article. It's not a blog, not a sales piece, not some random guy's post on some random forum, it's a fairly well written and researched white paper. If you need help understanding anything in the article,
this link and
this one will probably come in handy.
The best tire for a given rig is dependent upon where and what that rig will be doing its thing (and definitely not what other people in the area or on your favorite forum are using). If you wheel mostly in sand and mud, yes a wider tire is probably a better bet. If you wheel just about anywhere else (to include mall parking lots) the narrower tire is better.
The standard theory on tire size as I've seen it stated in the myriad discussions on the subject is that wider tires provide better grip because the tread covers more square inches. This is excellent justification for a wider tire IF your surfaces you're getting traction on are smooth and regular like tarmac. The alternate side to that theory is flotation; this applies only to smooth regular surfaces that are soft like sand or mud and deep enough that cutting through does not provide the greater tractive force. These are the ONLY instances in which that theory holds water.
Most of us, however, do not do our wheeling in deep soft sand and mud, we do it on rocks and sticks and dirt and such. These surfaces are hard and irregular, and do not require or benefit from any sort of flotation or distributed surface area (you're only going to be contacting the highest spots). If you read the white paper (the link), I don't think you have to get through more than the intro to see the point illustrated that a narrower tire grips these few high spots BETTER than the wider tires at the same pressure.
When wheeling you air your tires down not to increase the footprint of the tread, but to allow the tire to conform to the terrain and "grip" it. The paper uses the more appropriate term "mechanical keying". A narrower tire aired down and compared to an identically inflated wider tire will grip the available terrain BETTER than a wider tire due to the exact same effect as the flotation advantage had by the wider tires in soft terrain. Since the load on the wider tire is spread out more, it can't grip the available grippy spots as tightly (because that grip is spread out over more potential grippy spots) as the narrower tire.
Think in terms of specific scenarios:
A big rock:
Smooth, rounded, probably some sand or something dusted over the top
Advantage: draw. Unless the big rock is really big and really smooth, they're pretty much going to be contacting the same area
A bunch of smaller, but still decent-sized rocks:
Jagged, irregularly distributed, firm
Advantage: skinny tire. The narrower tire grips more firmly on fewer points as it deforms over them than the wider tire which is "floating" (borrowing the term) more loosely over the top of several rocks with less overall deformation.
Hard dirt:
Distributed, gives some but not much, irregular surface, will displace
Advantage: skinny tire. The narrow tire will, for the same reasons as the smaller rocks scenario, grip the parts of the terrain that are firm. Where the terrain is loose, the narrower tire has a better chance of cutting through to the more firma terra.
Slick Rock:
wide, generally flat textured surfaces with gentle curves, firm
Advantage: kind of a draw really... It's like driving over sand paper. You could pretty easily get by with just about any tire. It's called slick rock because it was slick for horses with their shoes and the hard wagon wheels, not because tires didn't stick to it like glue.
Mud:
Mud
Advantage: Depends on the depth... Narrower tire wins if the mud is shallow, wider if it's deep and soupy.
Sand:
sand
Advantage: see mud.
Snow:
snow:
Advantage: wider is better for deep snow to stay on top, narrower is better for less deep snow to cut through to the grippy terrain.
I'm going to go ahead and stop with the scenarios. Apply the logic to whatever you want.
If you use your 4Runner for anything other than occasional (or even regular) wheeling like, I don't know, a general mode of transportation, the narrower tires are better period. Better fuel economy, larger tires without body modification, etc. All those reasons stated a million times elsewhere. If your rig is built for extended adventure travel (long, unsupported trips over any and all terrain), you're generally better off with the narrower tires as they're better suited for a wider variety of uses. If you just want it to look cool in the parking lot with the tires sticking out, get the wider ones and try
this forum for future postings.
