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Tires are always the most important factor for every vehicle's performance.

When I bought a 2006 Porsche Cayenne with plans to build an off-roading storm chaser, I knew a tire choice loomed imminently. The previous owner lived at the top of a steep hill and constantly ground the Continental ExtremeContact DWS06 tires on high curbs, plus those Continentals simply wouldn't manage in the grit and grime even when relatively new. And I learned long ago that, simply put, tires are the most important component of a car's performance.

Some Cayenne owners go whole-hog and buy aftermarket wheels shod in 35-inchers. Not me—I want to avoid removing or trimming the bumpers and fenders, don't want wheel spacers that could potentially cause wheel hub damage over the long term, and don't want to sacrifice the incredible ride quality that makes a 955-gen Cayenne so great in the first place.

After narrowing my list of potential tires down to Cooper, Toyo, and Falken, I spoke with Toyo Senior Manager of Product Planning and Technical Services Todd Bergesen about options in the Toyo lineup that might successfully handle the unique challenges presented by a 450-horsepower super SUV with air-lift suspension and locking differentials. After the chat, Toyo sent me five Open Country A/T III tires for a long-term review.

Bergesen came to Toyo six years ago after 15 years working at an OEM auto manufacturer. He told me he loves Toyota Land Cruisers and currently counts three in his stable.

"I daily drive the 200 Series Land Cruiser," Bergesen said, "And it has our new Open Country A/T III tires on it. It’s an LT-metric 285/70-17. Of all the tires we offer and all the tires from our competitors we’ve tested, that is my absolute favorite."

On-road driving dynamics definitely fit in as a priority for me with the Cayenne, largely because my 1998 Mitsubishi Montero spent most of the last six months struggling to pass smog, so I asked Bergesen how he thinks the Open Country A/T III will perform on a Porsche.

"First and foremost, the on-road handling is much better with the A/T III over the A/T II," he admitted, "Because we did a much better job matching the tread lug rigidity with the body rigidity. When they are really well matched, they kind of work in concert. When you start to turn in, the vehicle doesn’t turn in too quickly and it doesn’t delay either."

But I discovered while researching the Open Country that Toyo managed to earn the Three-Peak Mounting Snowflake (3PMSF) winter rating, too, and Bergesen said that a major focus for the A/T III was to make sure that it performed well while cornering, holding speed, and braking in the snow—not just accelerating in a straight line as the federal test requires to get that snowflake printed on the rubber.

"I spent some time working out of a place in Lake Tahoe during the winter," he replied, "We actually did the entrance portion of the Rubicon Trail in my Land Cruiser in the snow and I was amazed at how far we were able to get. We never got stuck, we just decided to turn around."

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So far, the Toyos sounded pretty good to me—what better endorsement could I possibly receive? And Bergesen even knew specifically about the Cayenne, having almost pulled the trigger on a 955-gen Turbo S himself.

"The Porsche Cayenne is a very capable off-roader," he told me. "People that want to take them off-road are just now, it seems like within the last couple of years, are able to afford them to build them and take them off-road."

Part of the challenge for both the Turbo and the Turbo S comes down to tire fitment due to the fender lines, braking components, and ball joint placement. I didn't want to go too big and risk rubbing or damaging the intercoolers, but the massive brakes on my Turbo mean that 18-inch wheels are the smallest that can fit (and on a Turbo S, the even larger brake rotors and calipers make 20-inchers the smallest option). But when I started talking about sizes like 265/60R18 or 275/60R18, Bergesen stopped me to provide a quick education on the difference between P-metric and LT-metric tires first.

"I think that the biggest misconception as it relates to all-terrain tires or off-road tires," he coached me, "Is understanding the difference between a P-metric and an LT-metric tire. If your car originally was equipped with a P-metric and then you switch over to an LT-metric, inflation pressures change, the ride quality will change, the weight..."

Unless I wanted to step up almost to 33-inchers, turns out the Open Country A/T III options that will clear my intercoolers and ball joints only come in P-metric tires. At first, I felt some hesitation—wouldn't bigger, tougher tires necessarily do better and last longer? Well, then I might compromise that daily driveability somewhat.

"Any time you can keep that unsprung weight down, that will help with handling, stability, fuel economy, it’s just better all the way around. "

And Bergesen went even further in-depth on how lower tire pressure can actually reduce the risk of puncture, both on-road and off.

"Having that lighter weight tire at the lower pressure," he said, "It’s going to ride more compliant, but off-road, they do extremely well."

The P-metric A/T III option was starting to sound better, so I found myself very excited when Toyo offered to send me a set to mount on the Cayenne and review long-term in town, on the highway, in the dirt, and on the snow.

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As soon as the tires arrived, the noticeable differences stood out immediately. I found a set of original Cayenne wheels that matched mine for cheap on Craigslist—well, they matched other than remaining in borderline unbelievable condition, so I decided to swap the Continentals over to the clean wheels and mount the Toyos on the funky wheels, which I plan to fix up a bit and then either powder coat or paint matte black. But even on the dirty silver aluminum wheels, those Open Country A/T III tires already looked good thanks to a pretty aggressive tread for an all-terrain (versus, say, a mud-terrain).

"When it comes to all-terrain tires," Bergesen had said, "The level of aggressiveness varies greatly. There are a lot of trucks and SUVs that come standard with an all-terrain tire. And generally, the equipped versions are sometimes dulled down by the vehicle manufacturer or they just select a less aggressive design from the factory."

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"Our customers are looking for something that’s more aggressive," Bergesen stated matter-of-factly.

But just because the Open Country A/T III looks like a mud-terrain doesn't mean it's going to wear like one, thankfully.

“We have a 65,000-mile warranty on our P-metric tire," he said, "That’s a little bit higher than a lot of the competition. We launched it with 126 sizes. I think we’re at 132 sizes today and I think that might be the largest size lineup of any all-terrain available right now."

That range of size options helped to make the decision easier on me, too, since I could choose the best diameter and width to fit in the Cayenne's somewhat-cramped wheel well.

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As expected, compared to the Continentals, the Toyos felt much heavier even just rolling them around before mounting on the truck. But they would still be lighter than an equivalent LT-metric, if 265/60R18 came in LT-metric at all. I figured that added heft would sacrifice some on-road manners, given the old saying for high-end bicycles that, "An ounce on the wheel is a pound on the frame."

The total weight difference between the Contis and Toyos measures out to nine pounds each—or a difference of 30%, which sounds more extreme. Luckily, I already performed a stud conversion on the Cayenne using products from the popular aftermarket Porsche parts manufacturer Rennline, so actually getting the big new tires up and on felt relatively easy.

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Once I got the front wheels snugged up, I first checked the ball joint fitment. After all, I didn't have a set of wheel spacers sitting around in case the new 265 width, compared to the 255 Continentals, caused a problem with the ball joint due to the larger diameter. Though it looks tight, I could slide my hand between the tire and the end of the threaded bolt, so the fit should be good given that the wheel, tire, and hub all move as one. Any bigger than a scant 31-inch tire (really more like 30.5 inches) on the stock 18-inch wheels (with ET57 offset printed on the rim) will probably require spacers.

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I first mounted the tires with the Cayenne's air suspension set to the Terrain level, one higher than Normal, to give myself more room to work. With the body up high, the tires sat about two inches from the front of the fender liners where the intercoolers hide close by. But then, lowering the Cayenne to the Low setting started to make me a little nervous.

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At Low with the steering wheel centered, the tires still show over an inch of airspace from the front fender liner (you can see the air outlet slats that sit behind the intercooler in the photo above). And somehow, cranking the steering wheel all the way over, there's still about a hair's breadth of space—no rub at all. But given the prospects of turning while going over a bump or driving with caked-up snow on the tires, both of which could force the liner to bump into the intercoolers, I plan to install a set of relocation brackets from Eurowise to prevent any serious damage. And apparently, using a heat gun on the plastic liner afterward that job will provide more space for the bigger tires, too.

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I'm confident the intercooler job can wait, as long as I don't ride around in Low in town, go off-roading, or a snowstorm doesn't hit Mammoth anytime soon. In the meantime, I drove the Cayenne a bit on some hard-packed dirt roads and then out on the freeway to test out the new Toyos. So far, they're an absolute revelation in terms of road and wind noise—to the point where I suspect any noticeable increase is probably in my head (and especially compared to the aggressive Cooper Discoverer S/T Maxx rubber on my Montero).

Of course, the Cayenne drives so impeccably that even the slight tire differences do appear in certain regards, all of which I expected. The added rotational weight and diameter seem to affect torque delivery ever so slightly, as if I'm in the turbo boost a bit more to accelerate at the same speed. Good thing that twin-turbo V8 pumps out 457 lb-ft! And I'm glad those big brakes clamp down on massive rotors, since a little bit of braking power seems sapped by the size and weight, too.

But all in, the differences come across as less significant than expected. The Cayenne still feels sporty, though the ride-height and adjustable damper settings feel a little different. Normal for both now feels more like Terrain with the shocks on Comfort, while setting the height to Low with the shocks in Sport feels like what Normal for both did previously. Overall, call me 100% impressed by the Open Country A/T III after about 100 miles of driving. I'll be curious to see how they live up to that 65,000-mile wear warranty given the Cayenne's power and weight. I can't wait try them out for some more serious off-roading and winter is coming, so these tires and this Porsche will certainly see some snow soon.

Sources: continentaltire.com, coopertire.com, falkentire.com, toyotires.com, rennline.com, and eurowise.com.

Michael Van Runkle grew up surrounded by Los Angeles car culture, going to small enthusiast meets and enormous industry shows. He learned to drive stick shift in a 1948 Chevy pickup with no first gear and currently dailies his 1998 Mitsubishi Montero while daydreaming about one day finishing up that Porsche 914 project. He's written in various media since graduating from UC Berkeley in 2010 and started at HotCars in February 2018.