After the solid pavement ends, the demand for heavy-duty-truck capability that can travel off-road is pushed to an even higher level. Addressing this need, GMC undertook a mission to build the ultimate off-road heavy-duty pickup. Its design team’s solution is the formidable Sierra All Terrain HD Concept.

“It delivers the exceptional capabilities of the Sierra HD — hauling, towing and performance — and applies them to the toughest driving environments,” said Lisa Hutchinson, GMC product marketing director. It’s the “ultimate professional grade tool” for construction crews, ranchers and adventurers whose activities may take them to inhospitable terrain.

A design exploration to create the concept was inspired in large degree by the premium All Terrain Package offered on light-duty GMC pickups, said Ken Bakowski, Sierra marketing manager. The team started with a production three-quarter-ton heavy-duty frame, and then made modifications to enhance its off-road credentials.

“It’s got a short box and a crew cab, which we don’t make today on a three-quarter-ton,” Bakowski said, “but they put that on the frame, so they could push the wheels out to the corners to improve the approach and departure angles.”

The frame had to be slightly chopped — mostly off the back — so the 5-foot-9-inch-long cargo box would fit properly.

Power is supplied by a 6.6-liter Duramax Diesel and Allison 1000 six-speed automatic transmission combo, offered on 2011 GMC Sierra HD pickups. The Duramax delivers 397 horsepower and 765 lb.-ft. of torque, and provides up to 11 percent greater fuel economy than the previous version. Duramax grunt contributes to a 2,700-pound payload capacity, 13,000-pound conventional towing max and 15,600-pound fifth-wheel towing capacity.
“The key in our mind was marrying up heavy duty and marrying up a diesel to an off-road truck,” Bakowski said. “Now, we’re just trying to get your reaction to it.”

In its quest to turn heads of off-road enthusiasts, designers gave it a bold exterior, pumping up the body with large fender flares, extended from the body to shroud hefty 35-inch-tall BFGoodrich KMD “mud terrain” tires that wrap 20-inch machined-aluminum custom wheels. These wheels are stretched on a wider 73-inch track for greater stability.

“From every angle the concept looks the part of an off-road performer,” said Bakowski “It’s got a wide stance, tall profile and an increased ride height that provides a ground clearance of about 12 inches at the skid plates.”

The 4×4 Sierra All Terrain rides on specially developed Fox off-road shocks with remote fluid reservoirs, which are integrated into the wheel-house liners. These shocks team with front and rear jounce shocks, and custom front upper and lower control arms. Also enhancing off-road capability is an electronic front stabilizer bar disconnection feature, and automatic-locking front and rear differentials.
The Sierra All Terrain HD Concept has an enlarged grille that provides maximum airflow in tough conditions, and a forced-induction hood design that increases cooling air to the engine. Bumpers, which are streamlined to improve approach and departure angles, incorporate frame-mounted recovery hooks.

The cargo box is upgraded with a distinctive circuit-board-patterned composite bed liner; lockable, lighted storage compartments, tie-down cleats; two special compartments to access a 110-volt power outlet and air compressor; and a non-slip rubber pad on the tailgate.

Assist steps, which are a must for boarding the high-riding pickup, are motorized deployable types. They hide away during off-road use to maximize ground clearance.
The Sierra All-Terrain HD is cloaked in a custom Iridium Metallic paint, which is used to give the truck a more-precise and functional appearance. It’s a dark-charcoal color that reveals a reddish, anodized inflection when viewed from certain angles.

While battling the rough stuff, passengers sit comfortably in an upscale interior derived from GMC’s top-line Denali. Seats complement the exterior color with two-tone gray leather, featuring embossed carbon-style leather on the seating surfaces.

The steering wheel, instrument panel and center console also are leather upholstered.

Highlighting its infotainment system is a new navigation radio, which previews future radios that will be offered in GMC vehicles. Its 80-gig hard drive stores navigation-system map data, eliminating the need for a map disc and boosting storage capacity of music from portable devices.

This nav system of the future more efficiently gets the Sierra All-Terrain HD to that point where the pavement ends — and the work for GMC’s ultimate off-road truck begins. — Tim Spell, Motor Matters

(Tim Spell is the automotive editor for the Houston Chronicle InMotion section.)

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