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Thom Cannell Contributing Writer, GM-Trucks.com December 6, 2018 Last month Chevrolet invited us to test the Chevrolet Bison, a ZR2 derivative with distinctive upgrades that add to its already solid off road capabilities. Built off the already-capable Z7R2, American Expedition Vehicles (AEV) provided the collaborative additions that created Bison. It retains the class-exclusive front and rear locking differentials from ZR2, and high-zoot Multimatic DSSV dampers. The design of the Dynamic Suspensions Spool Valve dampers uses hollow cylindrical sleeves instead of familiar discs. These were used first on race cars including Champ cars, LeMans prototypes and F1 They provide superb off road damping, particularly on rough trails where they offer greater passenger comfort. Getting to the grit of it, a pickup is hard-pressed to have the approach angle of a Jeep, and impossible for a production bed to provide a really short departure. Nonetheless, Bison does a very good job of going over rocks. One of the AEV additions is a set of five hot-stamped Boron-steel skid plates to protect the oil pan, fuel tank, transfer case and front and rear locking differentials, which we tested extensively. “As this is the first Chevrolet vehicle we’ve given the AEV treatment to,” said Dave Harriton, founder and president of AEV, “we wanted to do something special with the industry’s first use of hot-stamped Boron steel.” We think he’s referring to the off-road industry, as hot stamped High Strength Steel is the basis for modern crash-worthy chassis. However, those skid plates kept the rocks out of our oil pan. Some of the Bison upgrades are more cosmetic than necessary, like replacing the bowtie grille a free-flowing CHEVROLET front grille, Bison decals on the bedsides and an AEV Bison logo on the tailgate plus an embroidered AEV on the floor liners and front head rests. Branding, eh? Performance-oriented changes include the stamped steel front and rear bumpers. The front bumper allows adding a winch (would you go off roading without a winch??), fog lamps and integrated recovery points. As a truck designed to venture deep into open spaces, Chevy added 31-inch Goodyear Wrangler Duratrac tires mounted on Bison-specific 12x8-inch aluminum wheels. We tested those, too, and they have plenty of grip on rocks, and in loose dirt. Note that the ZR2 cast-iron control arms and Autotrac transfer case are retained, along with the ZR2’s 3.42:1 axle ratio and front/rear tracks wider by 3.5-inches. Compared to a ZR1, Bison is lifted by two-inches. Our test vehicle was powered by the new 2.8-liter Duramax diesel (186 hp., 369 lb.-ft.) mated to a six-speed transmission. It was the crew cab model; with the short bed which including some AEV upgrades. On our highway drive towards an off-road park, we noted that the Bison was extremely quiet, and not just “quiet, for a truck”. No, it was quiet for any kind of vehicle, including a Cadillac. After switching the transfer case into 4WD-high, we bucked our way towards the promised bigger challenges. Along our trail—nothing extreme but way off the beaten path—we again noted there hadn’t been a single squeak, rattle, or buzz. The only odd sounds in the cabin were from the zippers on our camera bags. Bison’s frame is stiff; there’s no tweaking, everything is absolutely tight. There was no way to call out the suspension and its Multimatic spool-valve-type dampers, however the suspension was supple on the rough trail. Another noise-related note, we picked up no rock noise in the wheel wells despite being pushed around by potholes, rocks and dips. We might as well have been on the freeway, from a noise perspective. Our truck had almost every American Expedition accessory available. There were LED fog or trail-search lights on the hood, a ladder rack and a storage bin system mounted below a false bed. We only lacked the Baja-style intake snorkel. The bolted-on roof rack may have added stiffness to the already ultra-stiff box frame, which allowed the suspension do its work. Watching the vehicles ahead of us, we could see how steady the beds were, and how much the suspension was working. For a stock vehicle, there was plenty of travel available. Bison has a solid rear axle and independent front suspension, and there is a divide among off roaders and rock climbers as to whether a solid axle or independent rear suspension is better. Rock climbers seem to prefer solid rear axles. We thought the ZR2-based Bison chassis with a Duramax diesel made off roading almost a no-challenge event. The diesel engine was totally on-point with torque, needing only a light application of brakes for stability when balancing on rocks. Comparatively, those who had the standard V-6 gasser had a harder time of it, using more throttle to obtain torque, then having to feather the throttle and brake to stay on track. If you've never done rock crawling, you must apply power to get up, apply brake to stop, before being guided down in the correct direction. Yeah, it's really hard to see the front wheels through the engine. One of the options Chevy will offer through dealers is a shorter, cut off exhaust tip. We strongly recommend this if you’re going rock crawling. Many of us “modified” the longer exhaust tips when crawling off rocks. After crawling a rock canyon we grouped to head for lunch. Parked on a hill with loose sand and the tranny set in 4WD high, there wasn't enough traction. Locking the rear differential made climbing the hill as simple as stepping on the throttle, in that low traction situation. Having complete control over axles and each wheel made off roading and rock crawling easy, even for beginners. Note that, in our opinion, the Duramax doesn't deliver optimum fuel economy for the Bison. It's good, but not great. Where it shines is in torque availability for off roading. We can see the Bison with Duramax as a perfect combination for off road camping, adventuring, and modest towing. It's quiet. While on our rock crawls, there was never a sound from the chassis, no wracking, graunching, squeaks or rattles other than when we skidded over rock on those Boron steel protectors. It was billet solid. In fact, we'd go so far as to say our Bison was quieter than a standard Silverado and totally ready for any off road adventure. Interested in the Colorado ZR2? Join the GM-Trucks.com Colorado ZR2 Facebook Group!