The single finest example of an SUV ever created.
The single finest example of an SUV ever created. (Stuart Palley)
Indefinitely Wild

Everything You Need to Know About All-Terrain Tires

The ins and outs of choosing ones that offer the right size and load capacity for your truck

The single finest example of an SUV ever created.
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If you want to take full advantage of the traction provided by your truck’s four-wheel-drive system, you need to run a tire designed to grip the surfaces you drive on. And if those include both paved and unpaved roads, the tire you’re looking for is an all-terrain. Let me save you a bunch of money, hassle, and headaches, and show you how to find the right one for your specific needs. 

What Is an All-Terrain Tire? 

“An all-terrain tire is a jack of all trades, and a master of none,” says Todd Bergeson, the senior manager of product planning at Toyo Tires. Bergeson is responsible for engineering the tires my wife runs on her long-travel Land Cruiser, and he participated in the design of that vehicle—before joining Toyo, Bergeson worked as an engineer and product planner at Toyota. His résumé also includes other well-regarded 4x4s, like the 4Runner TRD Pro and the FJ Cruiser. 

What Bergeson is getting at is that, while other tires may outperform all-terrains on snow, dirt, or pavement, nothing else is designed to work as well across all those surfaces. 

Compared with a highway tire, an all-terrain tire will be equipped with a stronger bead (a ropelike ring that runs around the inner perimeter of the tire, holding it onto the wheel rim), tougher plies (the panels of steel or fabric mesh that lie under the rubber, adding strength and puncture resistance), as well as a rubber tread that’s thicker and designed to better withstand the cutting, tearing, and deformation caused by off-road surfaces. The pattern of that tread will also be designed to grip loose surfaces, while evacuating water, mud, small rocks, and snow as efficiently as possible. 

Unfortunately, all those traits do come with some trade-offs. Compared with a highway tire, an all-terrain tire will be heavier and louder and won’t offer quite as much grip on pavement. Bergeson says that more new vehicles don’t come equipped with all-terrain tires for just those reasons. “Most drivers don’t actually use their 4x4s off-road,” he says. “And they still want their trucks to be competitive with other vehicles.”

Consumers who buy rugged SUVs or pickups with the expectation that they’ll drive like a luxury car or a sports car often dictate the tire choices made by car manufacturers. If you bought an SUV or a pickup truck with the expectation that you’ll be able to use it off-road and in winter weather, you’ll need to change those tires. 

Bergeson’s Land Cruiser, on the western side of the Sierra Nevadas’ Rubicon Trail, wearing AT/IIIs
Bergeson’s Land Cruiser, on the western side of the Sierra Nevadas’ Rubicon Trail, wearing AT/IIIs (Todd Bergeson)

What’s the Right Size?

Larger tires will more easily roll over larger obstacles off-road. They also look cool. Unfortunately, larger tires will also reduce a vehicle’s effective gear ratio. As I wrote about at length in an article about people ruining their Tacomas, that can utterly destroy a vehicle’s fuel economy, performance, and off-road capability. 

Want to see the effect that fitting a larger tire size will have on your vehicle’s performance? Use these formulas.

(Original tire diameter) / (New tire diameter) x Vehicle axle ratio = Effective axle ratio with new tires 

So if you’re switching from the 30.5-inch tire that comes standard on a Tacoma to a 34-inch tire, given the Taco’s 3.91 gears, that will give you a new effective ratio of 3.50 to 1. Your performance will decrease by 11 percent. 

It’s hard to picture what that will look like in the real world, so this formula will help you understand that:

(Original tire diameter) / (New tire diameter) x RPM@MPH = New RPM at that speed 

Again, using the same Taco example, switching from a 30.5-inch tire to a 34-inch one will reduce engine revolutions at 60 miles per hour from 1,500 to 1,345 revolutions per minute. That’s also an 11 percent difference. Take that into the real world and see how your engine and transmission perform at the different RPMs. Just remember that the effects of altering your final drive ratio with larger tires are compound; while your engine will be operating at lower RPMs at a given road speed, it will also have less power. 

Wondering how much height a taller tire will add? Fortunately, that calculation is a lot easier. Simply divide the difference in tire diameters by half, and that will give you the increase in height that changing the tires alone will give you. This can be important in determining whether or not your truck will fit in your garage. 

What I can’t give you a formula for is how well a larger tire will fit on your vehicle. For instance, mounting 34-by-10.5-inch BF Goodrich K02’s (which actually measure out at 33 inches) to my Ranger required a two-inch suspension lift, chopping off the wheel-crash bars, and using wheels that spaced the tires outboard. And they still rub at full lock in reverse. Every vehicle and every suspension setup will be different, and the skill of your alignment shop plays a role in tire fitment, too. 

Does all that sound like a real pain in the butt? It is. There is no possible outcome here in which increasing your tire size does not cost you money and create an unnecessary hassle. So instead of trying to fit a larger size when you switch to an all-terrain tire, I’m going to make a controversial suggestion here: don’t. The best all-terrain size for you is almost certainly the tire size your vehicle left the showroom with. 

All those little numbers on the sidewall actually indicate more than a tire’s size. They can tell you a lot about how it will perform, too.
All those little numbers on the sidewall actually indicate more than a tire’s size. They can tell you a lot about how it will perform, too. (Toyo)

What About Load Ratings?

And you thought sizes were complicated! All-terrain tires come in three varieties, based on the loads they’re designed to handle: P/Euro-metric, LT, and flotation. 

A tire’s load capacity is determined by how much air it’s designed to hold. P/Euro-metric all-terrains come in either standard load (denoted by an SL or nothing in the tire’s size description) or extra load (XL in the size description). SL tires can be inflated to 36 pounds per square inch (psi), while XL tires can hold 42 psi. 

In either case, you should look up your vehicle’s gross vehicle weight rating (GVWR), found online, inside your doorjamb, or in your owner’s manual, and make sure any tire you fit is designed to support at least a quarter of that weight. 

“Think of a tire like a balloon,” says Bergeson. One designed to hold less air can be made thinner and lighter. One designed to hold more will need to be thicker and heavier. 

LT stands for light truck (you’ll see LT ahead of the tire size). In this verbiage, this denotes anything shy of a commercial vehicle. LT tires come standard on heavy-duty pickups, like the Ford Super Duty. The load capacity of LT tires is denoted by letters, typically B, C, D, E, or F. In the past, these letters indicated the number of plies used in the tire’s construction—in that same order: four, six, eight, ten, and twelve plies. With modern materials, that’s no longer the case. High-strength steel, nylon, or polyester plies don’t need to use as much material to provide an equivalent capacity to the cotton plies of yore, so tires now feature a ply equivalent rating. An E-rated tire, for instance, can now hold as much air as ten old plies, using just three plies made from modern materials. All you need to understand is that B-load tires can hold the least air, and therefore support the least weight, and that progresses on up to F, which can hold the most air and therefore support the most weight. 

As a tire’s load capacity increases, so does the air pressure it takes to fully inflate it. Where the maximum pressure on a standard-load P/Euro-metric tire is 36 psi (consult the table inside your vehicle’s doorjamb for recommended pressures; they’re typically a little lower than the maximum), the max pressure for an E-rated LT tire is probably 80 psi. (On LTs, maximum pressures vary with tire size. I’m glossing over some technicalities for brevity.) Not only will that be a thicker, stronger balloon, but inflated to sufficient pressures, it’ll also be a stiffer one. On the road, you’ll feel that. The thicker, stronger carcass of an LT tire, inflated to a higher pressure, will deform less over small bumps than a P/Euro-metric one, transmitting those movements to the suspension. And not only will more bumps reach the suspension, the momentum of that heavier tire will also be greater, so those bumps will effect the suspension more severely. It also takes more energy to accelerate or decelerate a heavier tire. All that to say: compared with a lighter P/Euro-metric tire, a heavier LT tire will worsen your vehicle’s ride quality, make it slower, and increase your braking distances. 

It’s important to emphasize here that if you upgrade from the P/Euro-metric highway tires that likely came with your vehicle to an aftermarket LT tire, you’ll need to run higher pressures than is suggested by your vehicle manufacturer on the road. LT tires require more air to reach optimal levels of inflation; fail to inflate one fully and the tire’s tread will cup inward rather than make uniform contact with the road. This will cause your tires to wear prematurely and create an awful lot of noise, and that reduced contact patch will combine with the soft, underinflated sidewalls to entirely ruin your vehicle’s handling. Use this calculator to determine the correct pressures for your LT tires. 

But carcass strength isn’t the only thing separating P/Euro-metric all-terrains from LT ones. Bergeson says that Toyo uses different compound materials for the two categories of tires, as well as different tread designs. 

“Our data says P/Euro-metric users spend at least 80 percent of their time on paved roads,” he says. So Toyo optimizes those tires for that use. On its new Open Country AT/III, for instance, Toyo employs a rubber compound with a higher proportion of silica, which enhances grip on wet pavement. And the tread pattern features smaller voids and more siping. (Sipes are the squiggly little lines inside the tread blocks.) The noise you hear all-terrain tires make is created by air passing through those voids. So making sipes smaller on tires biased to on-road use helps make those tires more civilized. Sipes enhance mechanical keying on slippery surfaces like ice, so adding more of them helps the P/Euro-metric AT/IIIs perform better in winter conditions. 

I asked Bergeson if the thinner, more flexible construction of a P/Euro-metric tire was less suitable for off-road use. “You’ll actually find that the more flexible tire deforms better over obstacles, which can help with grip and ride quality,” he says. It’s not true that plies used in those tires can lead to more punctures. While the strands used to construct the lighter tires aren’t quite as thick, they’re more densely woven, which works to prevent penetration equally well. The one area where an LT tire might be more resistant to punctures than the lighter option will come simply from increased thickness of the tread on the former. 

Where a P/Euro-metric AT/III is equipped with a tread depth of 13/32nds of an inch, the tread on LT sizes is 16/32nds of an inch deep. That means the rubber that the LT tires drive on is that much thicker. It’s also made from a different compound, with a lower silica content, and uses a tread pattern with larger voids and fewer sipes. Bergeson says that these changes are intended to increase the LT tire’s durability and performance off-road. Not only is the lower-silica-content compound more resistant to cuts, tears, and deformation caused by sharp rocks, but the larger voids are better at ejecting those rocks before they can cause damage. Fewer sipes are also less prone to picking up and being damaged by very small stones. With fewer of those sipes, the tread blocks on LT AT/IIIs better resist deformation, which restores some of the steering feel and stability lost by the larger voids. But those larger voids enhance traction on loose surfaces like mud. 

Notably, equipping LT tires with the ability to contain higher air pressures also gives them one feature that really helps off-road: because all that extra air requires a thicker, stronger bead, LT tires mount more securely to their wheel rims. This lets drivers safely run lower pressures off-road. 

Which brings us to flotation sizes. Whereas P/Euro-metric and LT sizes are listed in metric sizes (285/75R17 for instance), flotation sizes are listed in imperial specs (35×12.5R17). They’re typically produced in loads ranging from C to E and are usually available only in wider widths. Flotation tires are the most off-road-oriented all-terrains. Flotation AT/IIIs, for example, use a 17/32nds tread depth and even larger voids than the equivalent LTs. So they also require high on-road pressures but will be even more durable off-road, and even noisier on. Because they’re so wide, flotation sizes typically only fit modified trucks. 

Running P/Euro-metric all-terrains in your vehicle’s stock tire size is the easiest, most effective way to gain traction off-road and in winter weather without sacrificing too much in the way of road manners. Bergeson recommends only upgrading to an LT tire if you drive a lot of gravel (or if the weight of your vehicle dictates it). All the tiny, sharp, rolling rocks in that surface represent a unique challenge to tires, and it’s one the compound and voids used on the LT AT/IIIs are specifically designed to handle.

The AT/IIIs proved the perfect companion for the OE long-travel Land Cruiser, smoothing out its harsh traction-management system without unduly impairing the ride quality.
The AT/IIIs proved the perfect companion for the OE long-travel Land Cruiser, smoothing out its harsh traction-management system without unduly impairing the ride quality. (Stuart Palley)

Which All-Terrains Are Right for You?

Beyond size and load capacities, there are a couple other markings you need to consider. 

The first of those is the M+S stamp that’s present on most all-terrain tires and also many highway tires that advertise themselves as appropriate for mud and snow. The M+S standard is defined by the Rubber Manufacturer’s Association and is self-reported by tire makers, not certified by any independent body. To merit this stamp, a two-dimensional analysis of a tire’s tread pattern must demonstrate that at least 25 percent of the tread’s surface area is made up of grooves. M+S reflects no actual designed, intended, or tested traction in mud or snow, just that 25 percent groove area. Don’t rely on an M+S stamp to tell you anything about a tire’s performance. 

Conversely, the 3 Peak Mountain Snowflake (3PMSF) does represent tested performance to an actual American Society for Testing and Materials standard, but it is still self-reported by tire makers. And while 3PMSF is used by authorities to legally define a winter-capable tire, that’s a very limited standard. To score a 3PMSF rating, a tire only has to demonstrate traction on packed snow that’s 10 percent superior to a reference tire, that reference tire being a bargain-basement highway all-season tire from the early 1990s. Running a 3PMSF stamp may allow you to legally drive into Lake Tahoe, California, in the winter in a four-wheel-drive vehicle without snow chains, but it does nothing to guarantee that your drive will be safe. 

Until such a time that adequate performance standards for tires are enacted, we as consumers have to work with tire-maker claims, customer reviews, and independent tests conducted by enthusiast publications. If that doesn’t sound like an ideal situation for finding objective guidance around choosing the single most important component on your vehicle, I’m with you. 

My method for picking an all-terrain tire is to first figure out what size and load capacity I need, then to look around for the tire with those numbers that has been developed most recently. Assuming that materials and manufacturing technologies advance over time, I figure that should result in the latest and greatest product. But just to be sure, I’ll pull up a tire’s specs and compare them with competitors. The point of comparison that’s most important? Weight. For all the reasons described above, a lighter tire is a better tire if it otherwise provides the load capacity, durability, and traction you require. 

And that’s how I ended up putting Toyo Open Country AT/IIIs on my wife’s Land Cruiser. That tire was released last March, and in the LT275/70R18 E size that works best with the very complicated custom-suspension system on that truck, the 53-pound AT/III is four pounds lighter than the BF Goodrich K02—and over seven pounds lighter than the Falken Wildpeak AT3W

“Because we manufacturer the tire in America, we’re able to very carefully place rubber only where it’s needed,” said Bergeson when I asked him to account for that weight difference. He went on to explain that the AT/III’s light weight is achieved without sacrificing puncture resistance. Tread depth isn’t compromised on the design. Plus, the unique method by which the company layers its plies ensures that, while the E-rated AT/III is technically a three-ply tire, the plies overlap behind the tire’s sidewall, effectively protecting that area with six plies, while helping the tire retain better stability on the road. 

Those merits have been borne out in my time driving on those tires. That they’ve proven trouble-free off-road should be expected. What’s surprising is how good they are on dry pavement, on the road in rain, and on packed snow, too. Since we live in Montana, I still switch to a dedicated winter tire for that season, but running the AT/IIIs in the shoulder seasons allows us to confidently tackle even significant snow events without concern. 

My one prior frustration with that vehicle had been how invasive and lurch-prone its traction-management system is. But the level of grip provided by the AT/IIIs has smoothed it out and made it more effective and seamless in operation. I had no idea when I selected the tires that they were engineered by one of the guys who helped develop the Land Cruiser, but now that I know, it’s not a huge surprise that they’re the perfect match for the vehicle. 

What are the best all-terrain tires for you? Run through the formulas I listed above to determine the right size. Then decide whether or not your use case is more on-road or off, and choose either P/Euro-metric or LT tires to suit. (Consider a flotation size if you drive a highly modified truck.) See if you can find a lighter tire than the AT/III, and if you can’t, run those. Don’t be surprised if those tires make your truck feel brand-new, too. 

(If you drive an all-wheel-drive crossover, I still recommend the Falken Wildpeak A/T Trail. It’s the only all-terrain tire actually designed to work on Subarus and the like.)

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