Firestone’s Destination M/T2 mud-terrain: a desert tire?
Why would anyone mount mud-terrain tires on a vehicle that rarely leaves the Sonoran Desert?
Several people asked me that question, after I switched from the all-terrain tires I’d run for a decade or more on my 1973 FJ40, to a set of Firestone Destination M/T2s (after also considering the company’s Destination X/T, which has an all-terrain-oriented tread pattern).
My answer surprised some of them, who teasingly assumed I’d gone for the butch looks. And there’s no denying that the MTs look just right on an FJ40. However . . .
Most people assume that a mud-terrain tire is good for one thing: mud. And indeed the open, aggressive tread blocks of an MT tire are known to be effective at digging down for traction in shallow mud, and for the ability to shed sticky mud that tries to cling to the tire and fill in the tread so all you’re left with is a slick. Often a brief burst of throttle (a relative concept in an FJ40, granted . . .) will clear the tread and regain lost traction, when the same tactic would fail to do so in an AT tire with more closely spaced tread blocks.
However, an MT pattern is excellent at other tasks—and in fact better than an AT at some of them.
Consider deep sand, which most people would think is anathema to a mud-terrain tire. Not so—if it is aired down to the same level as one would an AT, an MT tire will perform perfectly well in sand, offering excellent flotation and traction—as long as you’re careful not to continue spinning the tires if you bog down. While any tire will bury itself when you do this, an MT tire will do so with considerably more enthusiasm. But there’s an upside I discovered, somewhat to my surprise although it makes perfect sense: if you are bogged (in any substrate) and deploy traction boards such as Maxtrax to extricate the vehicle, an MT tire will grip the traction board far more effectively than an AT tire, easing the recovery and reducing the risk of spinning and melting the studs on the board. I noticed this repeatedly while running sand recovery scenarios at the Overland Expo. Some vehicles with stock tires that barely had enough tread to qualify as an all-terrain pattern had an extraordinarily difficult time getting onto the board without wheel spin, while those on mud-terrains would tractor right up and out with zero drama.
What about mud-terrain tires on rocks? Most of the 4x4 trails near where we live in southern Arizona involve a lot of rock crawling in low range, and at this a mud-terrain tire is certainly equal if not arguably superior to an all-terrain tire.
To simplify a complex relationship, there are essentially three ways a tire can grip the surface beneath it.
Molecular grip. This is dependent on the formulation of the rubber in the tire. An extreme example of molecular grip is a high-performance sports-car tire. A tire with high molecular grip will have a soft compound good for sticking to the road but not good for long-term wear. While some tires designed for extreme rock crawling employ such compounds, it’s not desirable in a tire expected to last for tens of thousands of miles of use.
Micro-mechanical grip. This occurs when the texture of the tire’s tread keys into tiny irregularities in the substrate.
Macro-mechanical grip refers to the ability of the tire’s tread to mold around and grip larger irregularities, or indeed entire objects on the surface such as boulders.
Number three is where the large, discreet tread blocks of an MT tire excel. Think of the aggressive tread in the Vibram sole of a heavy-duty backpacking/mountaineering boot for a corollary. Indeed, when aired down properly, I found the M/T2s to perform exceptionally well on the rocks of the standard 4x4 route I use for reviewing vehicles, in Redington Pass east of Tucson.
The M/T2s at 22 psi wrapped around rocks for maximum traction.
The aggressive side lugs gripped especially well, and given the the thickness of those lugs plus three-ply sidewalls I didn’t worry about damaging the tires even when aired down to around 20 PSI.
Are there downsides to a mud-terrain tire? Of course. MT tires are noisier on pavement than all-terrain tires, to a greater or lesser extent depending on many factors, but basically . . . noisier. In an FJ40 this is not as big a factor as it would be in a more intrinsically quiet vehicle, but it’s still noticeable. My impression is that the Firestone M/T2 is quieter than the last set of MTs I had on the FJ40, but it’s been a while so that’s not hard evidence—and new tires are typically quieter than those with a few thousand miles on them. Around town the noise is no greater than a mild hum and barely discernible; at highway speeds it’s more of a medium/high-pitched whine.
More: MTs do not offer the same traction on pavement as an AT tire, for both handling and braking. You must adjust your driving to suit. You will also lose some fuel economy; just how much will again depend on several factors. My impression is that I’ve lost about a half mile per gallon on the 40 (figuring on my recent average of 16 mpg on the road).
All these factors were in play during my decision-making process. Years ago, when our FJ40 was our only overland vehicle (in fact for a time it was our only vehicle, period) all-terrain tires made more sense given more extensive use on paved roads and highways. Now, since we have a 70-series Troop Carrier for travel, the 40 is reserved for closer trips and for 4x4 training classes. Thus the M/T2s made perfect sense. I’ll be curious to see how they look and sound with a few thousand miles on them, but for now I’m very happy with the choice.
