Did you read the section on off road contact pressure and its effects on adhesion? More and more rock crawlers are actually using narrower tires. I found this write up as well. To the point I must say
"Less rotating mass- Easier to start and stop
Less reciprocating mass- Easier to dampen
Less wind resistance- Better economy and range
Less rolling resistance- Better economy and range
Easier to fit a taller/narrower tire with less lift
Lighter spare
Lighter tire
Lighter wheel
Less unsprung weight
Less weight and leverage on steering components, bearings, etc.
In terrain:
1. Less frontal resistance in mud and sand. Where is most of the increased contact patch (for flotation) gained? In the length, not the width. Tall and narrow allows for more length and greater deformation with less resistance.
It is as simple as understanding the coefficient of friction (COF), which is (Ff = Cf x Fv).
Ff= Friction Force
Cf= Coefficient of Friction
Fv= Force Vertical
As you make a tire wider, you reduce the Fv over a larger area, but gain Cf. As you make a tire narrower, you increase the Fv, but reduce the area of contact, which lowers the Cf. It is proportional, though there are times when the material interaction (lets say a drag tire on concrete) favors Cf, but those conditions rarely exist on the trail, on a perfectly flat surface. So, if a wide and narrow tires benefits with relationship to Cf and Fv are proportional, than the decision must be made on other factors, like weight, resistance, etc., as listed above.
Now of course, there are limits at both ends of the spectrum. Too narrow of a tire, and the torque applied to the surface, even with extremely high Fv (which a super narrow tire would have), would exceed the rubbers ability to resist tearing. Literally, burning rubber.
It is all a balance, with tires for most of the trucks we drive being ideal in the 9-11" wide range.
Big, fat tires are only for show trucks and tundra buggies. An expedition vehicle has an emphasis on simplicity, economy, durability and safety, none of which a 35x14.5 will give you. . ."
I am quoting a post from some Portal archives I dug up. The #1 section there under terrain hit it on the nail.
I can see where you like the wider tires for added protection for the rims, but this is why I still have the narrow rims (and the fact that new rims=more money) LOL. My 7 inch rims have lots of protection from my 10.5 inch wides. I can also see where a wider tire can do better in the "cracks" and not high side you.
As you stated, it depends on your needs. And in all honesty the width of the 12.5 is still "narrow" enough to conform to most of the "points" made in the article keeping in mind the weight of a Montero. I would say the sweet spots for the Montero would have to be a 31/ 9.50 to a 35/ 12.50 tire and depending on needs and let's not forget the tires on those rigs from Iceland. I would have to say without a doubt that they need a crazy wide tire vertically and horizontally.
