Slinging Mud with Rockproof, Nokian’s New Extreme Off-Road Tire

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Given the terrain-conquering mission of mud-terrain (MT) tires, it’s no surprise that the category is populated with some chest-thumpingly bold names. The Dick Cepek Crusher, for example, has a repeating skull-and-crossbones pattern molded into its sidewalls along with bone-shaped tread blocks. Nokian, of course no stranger to spirited names such as the one it’s best known for—its world-beating winter tire, the Hakkapeliitta, named after a Finnish battle cry—is entering the mud-terrain business with a new entry, called Rockproof.

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That tough label also explains its reason for being, as Nokian says the expansion into the extreme off-road category came about in response to feedback from commercial users of the company’s mining tires. It wasn’t a grievance with those monstrously sturdy tires themselves, but instead complaints that the companies’ light-duty vehicles operating in the mine’s vicinity were suffering repeated punctures. So Nokian, which appended an “n” to its name in 1995 to avoid paying royalties to the electronics company Nokia—although the tire company is the one headquartered in Nokia, Finland—adapted the compound of its extraordinarily robust mining tires with some additional off-road grip stirred in to create the Rockproof.

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The nondirectional tire is available in 13 sizes and in 16- to 20-inch diameters. Pricing has yet to be announced. The Rockproof features a tread depth of 20/32—roughly double that of a street tire—along with aggressive V-shaped sidewall elements for added ability to dig into whatever surface it happens to be rotating against. For maximum puncture resistance, there’s almost no siping, which keeps the Rockproof from earning the “mountain/snowflake” winter accreditation. But it does come pre-perforated with holes to facilitate the use of studs. The raised features at the base of the large tread blocks are there to keep stones from wedging between them, which could dig into the tire and cause a puncture over time. To better protect the steel belts and cords, the sidewalls are infused with aramid, a class of strong synthetic fibers also used in body armor.

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To test the Rockproof’s fortitude, we spent a couple of days exploring and navigating the extensive and challenging network of off-road trails at the Gerotek proving ground, a 2.1-square-mile former military test facility nestled into the steep South African landscape outside of Johannesburg. It’s a test site that Nokian regularly uses in its development of non-winter tires. There, we clawed up and inched down grades as severe as 30 or 40 percent, some slickened with sloppy wet clay and others teeming with sharp protruding rocks, along with slogging through mud holes a couple of feet deep.

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We drove three vehicles on- and off-road equipped with 17-inch Rockproofs of various widths and aspect ratios: a Toyota Fortuner and Hilux and a Dodge Ram. As you probably noticed, two of those aren’t familiar to U.S. roads. The Fortuner is closest to our 4Runner, but with a more Highlander-looking body. That means it’s underpinned by Toyota’s mid-size-truck architecture, complete with low-range four-wheel drive and a rear differential lock. The Hilux, which in this case was substantially lifted and otherwise off-road modified by Arctic Trucks, is the slightly more capable version of Toyota’s mid-size pickup that is sold around the world except in North America and a few other countries that get the Tacoma instead.

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For comparison purposes, a Land Rover Defender fitted with Nokian’s equally new but one category less extreme Rotiiva AT Plus tires rounded out our quartet. The Rotiiva competes with tires such as the Goodyear Wrangler DuraTrac and the BFGoodrich All-Terrain T/A KO2, which come fitted to the Chevrolet Colorado ZR2 and the Ford F-150 Raptor, respectively, and are about as extreme as factory off-road fitments come.

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Going slow is the key to judging off-road aptitude; given sufficient momentum, any vehicle-and-tire combination can summit a challenging grade or traverse a deep mud hole. That’s why, just like a cleanly driven lap of a racetrack, doing it right often doesn’t look exciting but there’s plenty of excitement, fun, and fear—such as stalling a manual-transmission truck with its nose pointed skyward on a steep, rocky incline—that can take place when off-roading, even at a walking pace. Although the Rockproof proved true to its name, as well as adept a climbing whatever rugged surfaces it trampled, we were most impressed by its performance through the mud holes. At a creeping speed, where the level of traction is immediately tangible, the Rockproof’s deep tread blocks felt more like paddles than tires as they pulled the trucks through the heavy mud, whereas the Rotiivas were doing a lot more fruitless spinning. Although we did wend our way through the Pilanesburg Game Reserve, where spotting a lion or an elephant proved much more difficult than the terrain, we didn’t get a chance for any high-speed off-road runs, or to put the Rockproof’s gnarly tread to work climbing any sand inclines.

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• A Guide to Off-Roading for the Uninitiated

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• The Battle of the Off-Road Beaters: Ford F-150 Custom vs. Geo Tracker, Jeep Cherokee, Land Rover Discovery

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• Baja Fresh: We Sample BFGoodrich’s New On/Off-Road Tire, the All-Terrain T/A KO2

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These are serious tires, essentially the off-road equivalent of a Michelin Pilot Sport Cup or Pirelli P Zero Corsa on the pointy end of the on-road-performance spectrum; they’ll get you home after an off-road adventure, but commuting with them will quickly become a chore. Although certainly not excessive for this type of tire, on pavement, the Rockproofs start singing noticeably above about 40 mph. And these tires are on average 16 percent, or seven pounds per tire, heavier than the Rotiiva AT Plus, and that unsprung mass, along with the ultra-rigid tread blocks, means that every ripple in the road is felt from the driver’s seat.

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But drivers who prefer to drive over rather than around the most challenging terrain now have another capable choice that prioritizes puncture resistance in the mud-terrain category.

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