How to Modify Your Subaru for Off-Roading

It’s trendy right now to buy a Subaru or similar all-wheel-drive crossover and modify it so it looks like it can go off-road. That trend is stupid. Let’s look at the reasons why such modifications utterly ruin your car, then talk about stuff you can do that might actually help it.

Five years ago, back when I lived in Los Angeles, I bought a Subaru Outback, then promptly set about fitting it with all-terrain tires, some flashy wheels, a few protection parts, and a ginormous roof rack. The end result turned out pretty well: it was a car that made camping trips possible but was still easy to use in a congested city and on long road trips. Detailing the modifications involved turned into one of the more popular articles I’ve ever written, and one I still receive almost daily questions about. Judging by all that interest and the number of cars I see on the road and on Instagram that have been modified nearly identically, a lot of people have copied that build. But they haven’t gotten it right. 

The key disparity between my intention and their reality was tires. The bargain all-season road tires that Subaru sells on its cars aren’t made for much more than a gentle commute. But tires are the most important component on any vehicle, the major determining factor in that vehicle’s capability on-road, off-road, and through inclement weather. So, seeking more grip and puncture resistance off-road and improved wet-weather performance, I fitted a set of lightweight all-terrain tires, with an emphasis on “lightweight.” What I got wrong was that I used and then wrote about a tire—the Maxxis Bravo 771—that can’t be found at most mainstream retailers, online or off. So most readers bought something else: something like the BFGoodrich K02. 

I actually ran a set of K02’s on that old Outback for about a month but ended up pulling them off and remounting the 771’s at the first available opportunity. Why? Because they totally ruined the car. Let’s start there. 

Two Types of Weight

When we talk about the weight of any vehicle, we need to talk about two types of weight: sprung and unsprung. Sprung weight is anything carried above the vehicle’s suspension—the body, the frame, the passengers, and their luggage. Unsprung weight is anything below that suspension—the wheels and the tires, basically. 

Ever wondered why big, heavy SUVs and luxury sedans ride so comfortably? Why they seem to smooth out bumps and potholes that smaller, lighter cars bounce harshly over? Well, it’s due to the ratio between sprung and unsprung weight. 

The more unsprung weight a vehicle carries relative to its sprung weight, the greater the influence those unsprung components will have over the vehicle’s passengers. Hit a bump in a car with light wheels and tires, and the force those parts generate as they move up and down will be minimal in comparison to the weight of the vehicle itself. Hit a bump in a car with heavy wheels and tires, and the force those parts generate will have a lot of effect on the vehicle. This is what you feel every foot of every mile you drive. 

Unsprung weight also impairs a vehicle’s ability to accelerate and brake. The heavier your wheels and tires are, the harder your car will have to work to change their velocity. If you’re trying to accelerate, then the weight of your wheels and tires will work to resist your engine’s power, ultimately reducing the amount of horsepower that reaches the road. If you’re trying to stop, then that unsprung weight will try to keep spinning as you apply the brakes, decreasing the ability of your brakes to slow your car down. 

This effect can be measured. A stock 2018 Subaru Crosstrek makes a modest 141 horsepower when measured on a wheel dynamometer. Fitted with those heavy K02’s mentioned above, that same vehicle makes just 127 horsepower. The only difference is the heavier tires; those alone reduce performance by 10 percent. You can expect to see a similar impact on fuel economy and braking performance. 

I noticed this when I switched from those 771’s to the K02’s on my Outback. Adding roughly ten pounds of unsprung weight per tire, that car’s performance was noticeably blunted, and it lost about three miles per gallon of fuel economy—again, about 10 percent. But that wasn’t the worst problem. Because lightweight unibody crossovers carry less noise insulation than heavier body-on-frame trucks and SUVs, the noise created by the aggressive tread and inflexible carcass became unbearable at highway speeds. What was once a quiet, luxurious drive became as loud as riding in an airliner. 

But Outright Weight Is a Problem, Too

Let’s keep using that Crosstrek as an example, specifically the one pictured up top. It was created by Warn, an American manufacturer of high-quality winches. It’s lifted and wears the kind of off-road accessories that are trendy right now. 

With about 12 pounds of added wheel and tire weight per corner, plus the weight of a fifth full-size spare (50 pounds), a winch and its mounts (85 pounds), a steel tube bumper (100 pounds), an awning (25 pounds), a roof rack and off-road lighting (best guess: 75 pounds total), and skid plates (50 pounds), it’s carrying about 430 pounds of additional weight. That is a problem. [Correction: Warn clarifies that the winch and bumper pictured here weigh 88 pounds total, not 185 as first written.]

The maximum payload a Crosstrek is capable of carrying is 1,104 pounds. All the crap bolted to our example eats up more than a third of that. Other crossovers have similar limitations; for example, the larger Outback can only carry 948 pounds. That payload rating must include the vehicle’s passengers and also the weight of anything they want to bring with them. With only 674 pounds to work with, you could overload the example Crosstrek with three large adults. And that’s before you account for fuel, camping gear, or even dogs. Exceed that max payload rating—particularly on a rough dirt road—and you run the risk of breaking components in the suspension and drivetrain. It's common to see Subarus wearing larger, heavier tires break stuff like their CV joints, especially while loaded down with too much weight. You can expect to have your warranty claim denied if you damage your car under such circumstances. 

Say Goodbye to Fuel Economy

I was chatting to a former Thule engineer a few weeks ago about wind-tunnel tests. He explained that, in the brand’s extensive wind-tunnel testing of roof racks, it found that any load carried on roof rails created an “air dam” beneath it. What’s that mean for you? The total height of any load, including any open space beneath it, creates a unified barrier to the wind atop your vehicle. This totally spoils any car’s carefully designed aerodynamics and will carry with it net impact on noise levels inside the vehicle, fuel economy, and outright performance. 

How much extra height is on the top of our example Crosstrek—a foot? In addition to the added weight and increased unsprung weight discussed above, this is going to have a massive impact on fuel economy. A stock Crosstrek returns a very good 27 miles per gallon (city) and 33 miles per gallon (highway). I’d imagine that, at higher speeds, the pictured vehicle struggles to average much more than miles per gallon in the low twenties. 

Fitting a rooftop tent to a crossover would reduce fuel economy even more, while raising your center of gravity so much that it’ll just totally spoil your handling, while likely damaging your roof. 

What Impact Does All This Have on Safety? 

On a body-on-frame truck, a winch is mounted between the frame rails. So in a crash, that vehicle’s crumple zone and sensors are essentially unimpaired by the fitment of such a device. Can you say the same if you mount a winch and a light bar to the front of a unibody crossover like our example Crosstrek?

No crash tests have been carried out on this vehicle (or anything like it), so it’s impossible to say for sure. But the winch sits in front of a crossover’s crash structure. This will alter the way that the car’s structure experiences forces, likely in ways that may not seem readily apparent. Take the airbag sensors, for instance. On modern vehicles, those are actuated by accelerometers mounted inside the vehicle’s dashboard. By transferring the forces of a frontal impact directly into the vehicle’s frame, the winch could get in the way of the bumper’s ability to absorb the energy of low-speed impacts. Could this additional force cause the airbags to fire at lower speeds than what they’re intended for? Again, it’s impossible to say, but this could cost you thousands of dollars in what might be the result of little more than a parking-lot mishap. And by pushing a large, solid, heavy winch into your car’s engine compartment in a big crash, it could also impact your Subaru’s ultimate ability to save your life.

I’d want answers to these questions before I fitted a winch or aftermarket bumper to any vehicle I’m driving, but makers of off-road accessories don’t typically perform crash tests on the parts they sell. And you’ll be making such a crash more likely by impairing your vehicle’s braking ability with all that added unsprung weight. 

Why?

You probably bought a crossover instead of a truck or SUV because it gets better fuel economy, is nicer to drive on paved roads, and tends to be both more affordable and safer. Yet by fitting it with these modifications, you’ve basically just paid thousands of extra dollars to compromise all those benefits. And you haven’t really gained any capability on dirt. 

As I detailed in this article, no all-wheel-drive system, no matter how many acronyms it carries, can match the traction created by a basic four-wheel-drive setup. And it’s angles, not ground clearance, that determine your ability to clear obstacles. Even with all the farkles on our example Crosstrek, its off-road capability is essentially the same as the bare-bones stock alternative. You’ve wasted your money and ruined your car. If you really want to go off-road, why not just spend those extra thousands on a Toyota 4Runner instead? In stock form, one of those will run circles around even the heavily modified Crosstrek we're discussing throughout this piece. 

The Right Way

You are right to want better tires. What you missed is that weight is one of the most important factors in determining a tire’s ability to perform on your vehicle. K02’s are heavy because they’re designed to support the weight of a big, heavy, powerful truck, not your little crossover. So they’re equipped with a thicker carcass, carrying multiple steel belts. You don’t want those. 

Fortunately, finding an all-terrain tire designed for lighter vehicles has become easier since 2015. With its new RAV4 TRD Off-Road, Toyota tried to bring legitimate dirt-road capability to the crossover space for the first time. And in doing that, it commissioned Falken to design a tire that’s both lightweight and good off-road. The resulting A/T Trail is widely available and comes in sizes intended to offer a direct replacement for stock tires on other popular crossovers. In the 225/60R17 size that fits a Crosstrek, they add only five additional pounds per corner, about half the weight penalty an equivalent K02 or similarly heavy all-terrain tire will bring. 

Importantly, those tires are also designed with a crossover's unique performance needs in mind. A rubber compound that contains a high proportion of silica enables them to safely grip wet pavement. The tread pattern is optimized to balance low noise levels and good water clearing abilities with enough off-road traction and winter performance for the kind of conditions crossover drivers will be able to tackle. I fitted a set to the old Outback that my cameraman drives and can report that the effect is transformative. They’ve added a significant amount of traction and confidence on-road and off, without perceptibly impairing ride, performance, or fuel economy. 

“The KO2 will deliver better off-road performance than the A/T Trail, but will do so at the expense of fuel economy, noise, comfort, handling, and even wet safety,” acknowledges Drew Howlett, who developed the tire for Falken. He goes on to explain that the tire's unique suitability for crossovers isn't really the result of novel technology, but simply a different approach. Where other all-terrains are developed for and on heavy trucks, Falken specifically developed the A/T Trail for and on a RAV4 and a Crosstrek. “Most crossover owners who opt for a KO2 in place of their [stock] tire only notice how much louder the tire is, and how their fuel economy drops, not how much worse the tire makes the vehicle handle and stop,” Howlett continues. “That is until they find themselves in an emergency situation. Our testing showed the A/T TRAIL stops just over 15 feet shorter than the BFG KO2 from 60mph to 0mph on wet pavement.”

You can totally fit those Falkens to your stock wheels and stop there. You’ll have achieved a noticeable improvement to your vehicle, with little to no downside. Those of you who are more engaged with the automotive world may want to go a little further. My best advice to you would be to keep the emphasis on “little.” Skid plates like those made by Primitive Racing are all the protection you need. If you must fit a roof rack, make sure it’s one you can easily remove when you don’t need it—then remove it when you don’t need it. If you’re worried about getting stuck, keep a pair of Maxtrax Minis in your trunk. Carry a small air compressor and a tire-repair kit, rather than a full-size spare. Just don’t overdo it, and you’ll have a capable and functional vehicle.