Because a four-wheel-drive sport-utility vehicle or pickup is designed to go off-road, it makes sense to buy tires designed for off-road duty. Besides, those macho all-terrain tires with the big white letters on the sidewalls look cool, don’t they?
But if “off-road” means occasionally taking a dirt path or a shortcut across a soccer field, you might be wasting money on all-terrain or off-road tires. They may not last as long as highway tires, and you could be subjecting yourself and passengers to unnecessary roughness and noise.
Even the companies that sell tires under rugged-sounding names such as Dualer A/T, Timberline A/T and Wrangler MT/R that conjure images of fearless outdoors types charging up mountains in their SUVs, say most people buy them more for show than off-road go.
“SUVs are more likely to be driven to the opera than off-road,” said Bill VandeWater, a consumer product engineer for Bridgestone/Firestone. “For a normal consumer, who is using his SUV to drive to and from work and maybe loads it up two or three times a year for a family vacation, passenger-vehicle tires should be fine.”
Kevin Mahl, Goodyear’s product manager for light-truck tires, says consumers want the rugged look of all-terrain tires even if they never get off the beaten track, let alone off-road.
“I think it is more the visual appeal than need, and our research shows that,” Mahl said. “They want a more aggressive tread pattern than what comes as original equipment, especially with pickup trucks. They want a more macho look.”
And they’re willing to pay for it. The Ford F-150 has standard P235/70R16 tires, but Ford offers wider all-terrain tires for an additional $400 and more rugged heavy-duty tires for $695. Both have raised white letters on the sidewalls instead of the standard blackwalls. Most pickups and SUVs offer all-terrain tires as options.
All-terrain and off-road tires are more expensive on the replacement market as well. Goodyear, for example, in the 235/75R15 size lists suggested retail prices of $155 for its RT/S all-season tire, $168 for the AT/S all-terrain model and $181 for the off-road MT/R model.
Passenger or truck?
Trucks can be equipped with passenger-vehicle tires (called P-metric by the tire industry) or heavier-duty light-truck tires. The letter “P,” as in P235/75R15, on the sidewall identifies passenger tires, and light truck tires are labeled LT.
Questions about which type of tire SUVs and pickups should use are expected to be an issue in Congressional hearings that start this week in the wake of recalls of nearly 20 million Firestone tires.
Last year, Firestone recalled 6.5 million ATX, ATX II and Wilderness AT tires, most of which were installed as original equipment on the Ford Explorer, all in the P235/75R15 size. Tread separation on those tires has been blamed in 174 deaths and more than 700 injuries.
In May, Ford announced it is replacing nearly 13 million Wilderness AT tires in 15-, 16- and 17-inch sizes after its tests indicated the tires become failure prone as they age. Firestone maintains the tires are safe. Ford is replacing the tires with brands other than Firestone and is offering both highway and all-terrain models.
The Congressional investigation will look at several brands of tires and trucks to determine if passenger-vehicle tires are rugged enough to be used on sport-utilities like the Explorer and pickups. All 20 million tires recalled by Firestone and being replaced by Ford are passenger tires with an all-terrain tread design.
The tire companies say passenger tires are safe and, based on the way the vehicles are driven, a good choice for most SUVs and pickups.
Within the passenger and light-truck tire categories, consumers have options. Highway tires are for on-road use and usually have an all-season tread to provide good traction in rain and snow (designated M & S on the sidewall for mud and snow).
All-terrain tires also may have an all-season tread, but they are intended for on- and off-road driving and are generally heavier, stiffer and noisier than highway tires. Off-road tires are the real brutes, coming in larger sizes with deeper treads for slogging through sand and mud, thicker sidewalls that resist punctures on rocky terrain and a rough, raucous ride on pavement. As the name suggests, off-road tires are not available as passenger tires.
Vehicle manufacturers estimate only about 5 percent of SUV buyers go off-road, so their main goal with the standard original-equipment tires is a quiet, comfortable ride. Mahl says passenger tires outsell truck tires 3-to-1 as original equipment on light trucks. However, when owners replace their tires, more choose light-truck tires over the softer-riding passenger versions.
Though all-terrain tires can cost more than highway tires, their tread life usually is not guaranteed for as many miles. Bridgestone gives its Dualer H/L highway tire a 60,000-mile tread warranty and the Dualer A/T all-terrain model a 50,000-mile warranty. Firestone has corresponding warranties for the highway and all-terrain versions of its Wilderness tires.
Most all-terrain and off-road tires classified LT do not have a mileage warranty, only a guarantee that covers defects in workmanship (a practice that also applies to high-performance car tires). For instance, P-metric models of Goodyear’s Wrangler H/T have a 60,000-mile warranty, but the LT versions have none.
The reason is “because it is not known how the tire will be used,” Mahl said, and the more robust construction of LT tires means they usually are on vehicles that see harder use. “LT tires are for someone who is using them off-road or in a utility situation, where they’re carrying a [heavy] load or pulling a trailer.”
Highway tires may last longer than all-terrain or off-road tires, and some premium models carry 80,000-mile tread warranties
“A highway tread design will wear a little better than an all-terrain tire,” Mahl said, though that depends on the driver and how the vehicle is used.
“The No. 1 thing to ask yourself is how you’re going to use the tire,” Mahl advises light-truck buyers. “A lot of original-equipment customers would like to see a more aggressive tire on their vehicle, but ask yourself how you are going to use it.”
In other words, choose the right tool for the job.
“You don’t really need light-truck tires if you never go off-road and just carry passengers on-road,” Mahl said. If a truck is driven like a car, all-season highway tires are a good choice. For those who occasionally go off road, a P-metric all-terrain tire may be more appropriate.
Off-road tires such as the Bridgestone M/T (Max Traction) and Goodyear Wrangler MT/R are strictly for enthusiasts who engage in the boulder-bashing, mountain-climbing adventures frequently depicted in SUV advertising. The stiff, knobby tread design of these tires makes them a poor choice for on-road driving.
“You can hear them a mile away on the highway,” VandeWater said. “They’re for people who are going off-road every weekend,” driving through sand dunes, hill climbs and other rugged terrain.
Tim Fry, a senior development engineer for Goodyear, says the Wrangler MT/R was designed for extreme use such as the Rubicon Trail in California, considered by some the ultimate off-road test.
“But people are putting them on SUVs that get 100 percent highway use. It’s the wrong application,” said Fry. “The MT/R is noisier and stiffer and will not be as comfortable as a highway tire. The customer really wants a tire with the right visual effect instead of an all-terrain tire.”
The look
Tire companies address that desire with tires such as the Goodyear Wrangler HT, Firestone Wilderness HT and Michelin Cross Terrain SUV, all-season tires meant for highway travel with an aggressive-looking tread that mimics off-road tires. They also sport the requisite billboard-style white letters on the sidewalls.
Michelin designed the Cross Terrain for SUVs with the goal of giving it the look of an off-road tire and the ride of a passenger-car tire.
“The vast majority of SUVs don’t leave the road, so the [vehicle] manufacturers want to give the buyer the appropriate tire for that kind of use,” said Mike Wischhusen, Michelin’s product marketing director for passenger car and light truck tires. “Buyers want the image of a tire that’s rough and tough, but it has to be well-mannered, quiet and comfortable.”
Fuel economy should be higher with highway tires because they have less rolling resistance due to their smoother tread design. However, the differences are so slight that most people probably won’t notice unless they meticulously measure gas mileage, Bridgestone/Firestone’s VandeWater said.
Highway tires, however, are the wrong choice for rugged terrain, even on a 4WD truck.
“You can go on the beach and go through snow safely with them,” Mahl said. “I don’t think you want to go on the Rubicon Trail with those tires. In fact, I know you don’t.”
Regardless of the type of tire, inflation pressure is a key factor in how much weight–or load–a tire can safely carry. Low tire inflation is one of the factors cited by the industry in tread failure in the Firestone recall last year.
According to tire-industry standards, a P235/75R15 tire set at the maximum pressure of 35 pounds per square inch can carry 2,028 pounds. At 20 psi, the tire can carry 1,543 pounds.
Load ratings are based on the volume of air a tire can hold, allowing larger tires to carry greater loads, and the air pressure. The maximum inflation pressure and load rating are stamped on the sidewalls.
All cars and light trucks come with a tire placard that lists recommended tire sizes, inflation pressures and load limits, but determining whether a vehicle’s load (the weight of the vehicle, occupants and cargo) exceeds the maximum may not be easy.
“It’s really quite a problem, and I don’t think you really know in most cases,” Goodyear’s Fry said. “As an industry, we need to do a better job of explaining this.”
He recommends consulting a tire dealer for advice on load limits and proper inflation pressure and adds, “You’re better off being a little over-inflated than under-inflated.”
To estimate the load on each tire, Wischhusen suggests adding the weight of the vehicle to the weight of its contents and dividing by four. Check that against the maximum load on the sidewall or the tire placard.
For those unhappy that the LT tires are too stiff or noisy, Wischhusen tosses out this caution: P-metric tires may be quieter and more comfortable, but they will not have same load-carrying capability or performance in extreme conditions.
