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First Look: GMC All Terrain Sierra HD Concept

Taking on the big guys?

by on Dec.16, 2010

The GMC Sierra All Terrain HD concept will make its world debut at the North American International Auto Show in Detroit.

Could GMC add a halo off-road truck to its full-size pickup lineup? The diesel-powered GMC Sierra All Terrain Heavy Duty Concept — which will debut next month at the 2011 Detroit auto show — points to how the “professional grade” brand thinks it might deliver a credible competitor to the Ford F-150 SVT Raptor and the Ram 2500 Power Wagon in the current or next-generation Sierra HD.

The light-duty Raptor and heavy-duty Power Wagon are two of the most capable off-road pickup trucks ever to jump or climb off the showroom floor. We love both because these purpose-built rigs can go places and do things off pavement that would kill lesser trucks within yards of the trailhead. The Raptor flies across the desert at high speed, like a Baja trophy truck, while the Power Wagon can rock crawl over the toughest terrain you’ll find in Moab.

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But these traits make an apples-to-apples comparison of the trucks difficult because their off-road strengths lie at opposite ends of the wheeling spectrum. This is where GMC smells opportunity.

The short-box crew-cab Sierra All Terrain HD threads the needle between the half-ton Raptor and three-quarter-ton Ram 2500 Power Wagon by carving a new niche that blends the off-road prowess and features of the Ford and Ram trucks with a few new innovations.

 

The Ford F-150 Raptor is one of several intended targets should GMC put the Sierra All Terrain HD Concept into production.

As with all off-road pickups, the heart of the All Terrain HD is its suspension. The concept’s running gear makes good use of the Sierra’s overhauled box ladder frame, shocks, springs and axles that were introduced for the 2011 model year.

“The capability-enhancing attributes of the Sierra All Terrain HD build on the already outstanding capabilities offered in the all-new production Sierra HD trucks,” said Lisa Hutchinson, GMC product marketing director. “Although it’s strictly a concept, it’s a pretty realistic one.”

But some heavy-duty off-road users have criticized GM’s HD pickups for their torsion bar independent front suspension instead of a coil spring solid front axle, like Ford’s and Ram’s heavy-duty pickups use. An independent front suspension generally provides better ride comfort on- and off-road, which the light-duty Raptor uses for high-speed desert running. A solid front axle allows higher ground clearance and superior articulation — for low-speed rock crawling — which the Power Wagon excels at.

The All Terrain uses independent front suspension to its advantage. For improved off-road stability, the standard A-arms have been replaced with custom double-wishbones and offset wheels that give the Sierra a 73-inch track up front — 4.2 inches wider than the current Sierra HD and nearly identical to the Raptor’s 73.6-inch track.

The All Terrain’s rear track is also 73 inches from a stock rear axle and offset wheels. Ram Power wagon’s track is 68.3 inches in front and 68.2 inches in back.

An independent front suspension isn’t the only thing the Raptor and All Terrain HD have in common. They also share Fox Racing internal bypass shocks, though instead of piggyback reservoirs in back, the Sierra has remote reservoirs (for improved capacity and cooling) integrated into the truck’s wheel wells at all four corners.

If GMC wanted to get Ford’s attention, this should do it. Fox’s shocks are the key components that give the Raptor such awesome wheel travel at high speeds off-road.

Racing’s internal bypass technology is slick and maintenance-free. Instead of placing the oil routers outside the shocks, Fox sealed them inside the main tube so that they can’t be adjusted. The valves have been replaced with very small gates, precisely placed for optimal damping in all conditions. Hardcore off-roaders might not like this setup, but it solves several potential issues both for GMC and for less-obsessive desert-running enthusiasts. There are no external bypass tubes to be damaged by offroad debris striking them; there are no worries about check-valve durability; and the shocks can be tuned specifically to the Sierra All Terrain’s off-road character.

In the Sierra, Fox’s long-travel dampers add 2 inches more travel up front (11 inches total) and 3 inches in the rear (11.75 inches total) over the Sierra’s stock monotube shocks.

While Ram doesn’t offer Fox shocks for the Power Wagon, Chrysler Mopar performance parts division will also feature Fox Shocks as part of its aggressive Ram Runner dealer-installed off-road package for the light-duty Ram 1500.

We wouldn’t be surprised if this latest Fox development effort causes a major rift with Ford, which brought prominence and high-volume production expertise to Fox in OEM off-road applications.

The All Terrain HD also borrows a cool trick for its front suspension from the straight axle Power Wagon. The Ram features a front sway bar disconnect system that increases wheel travel and articulation to climb over tall obstacles. The Sierra All Terrain also has an electronic front stabilizer bar disconnect.

A slick new piece of suspension kit introduced on the Sierra All Terrain HD that neither the Raptor nor Power Wagon offer are front and rear jounce shocks. Jounce shocks, in contrast to common urethane jounce bumpers that pickup trucks use to cushion overload situations, work by providing secondary compression and rebound support over tough terrain to prevent the truck from bottoming out. Instead of oil, they use nitrogen gas and lack internal valves for simplicity and smooth damping operation.

The Sierra All Terrain’s jounce shocks were co-developed with Light Racing. The All Terrain HD has electronic locking differentials in the front (like Power Wagon) and rear (like Power Wagon and Raptor) axles for maximum traction in slippery spots. Even if the All Terrain HD Concept never makes it to production, we expect we’ll see a similar front e-locker option available in future GM full-size pickups based on lessons learned from the discontinued Hummer brand and the extra capability the feature brings to a truck.

For improved ground clearance, the Sierra All Terrain’s ride height has been raised by about 3 inches over the stock Sierra’s ride height. It’s 21.1 inches at the rocker panels and 11.8 inches at the skid plates.

Contributing to the lift are aggressive 20-by-9.5-inch six-spoke custom 8-lug wheels with 35-inch-tall BFGoodrich 325/60R20 tires.

 

Form follows function when it comes to the GMC Sierra All Terrain’s exterior design.

Carl Zipfel, the lead designer for the Sierra All Terrain, has designed trucks at GM for more than a decade, including some of the coolest concepts and production rigs such as the GMC Terradyne, Terra4 and Hummer H2 and H3 trucks.

“The design of the All Terrain HD is an expression of its capabilities — strong, functional and absolutely professional grade,” Zipfel said. “We’re excited about the design elements and exploring how the could apply to future GMCs.”

Though the Sierra All Terrain is based on the current GMC Sierra HD, we believe it hints at styling elements that will be found in the next-generation Sierra pickups expected around 2013.

The prominent front end features an in-your-face three-bar grille and chrome surround that reminds us a bit around the top of the first-generation GMC Yukon Denali.

The lower portion of the grille blends smoothly into the front bumper and integrated skid plate. The hood cleanly drops the center louver found in today’s Sierra HD and replaces that plastic island with two integrated functional hood vents to help bleed heat from the engine bay. Instead of a Coke-bottle shape like the Raptor has to cover its wide stance, the Sierra All Terrain uses massive flares over the wheel housings. The side doors are shared with the current Cadillac Escalade, and auto-folding side steps extend and retract to help with ingress and egress.

The Sierra’s extra-short 5-feet-8-inch cargo box draws inspiration from the light-duty Ram 1500’s optional RamBox side-saddle storage, with its own built-in compartments that don’t eat into valuable open bed space.

When it comes to off-roading, it’s all about keeping the shiny side up, but to protect the bottom of the truck from brutal terrain, the All Terrain has a composite underbody shield that covers the powertrain, fuel tank, exhaust and diffs. The rear bumper has an integrated skid plate that aids the truck’s departure angle while blending together.

One of the areas most in need of improvement in the current GMC Sierra HD is the cabin space. It looks dated compared with the Ford and Ram interiors.

The Sierra All Terrain HD sticks with the current interior instead of previewing the next-gen Sierra but it addresses some of our cockpit gripes by using new premium materials, such as stainless steel mesh and satin chrome. Two-tone leather seats feature slick carbon fiber patterns embossed in the skin and red stitching around the seams. The instrument panel is also wrapped in leather.

A new navigation radio previews the same head unit that will be offered in future GM vehicles, so expect to see this in the next-gen Sierra and Chevy HD pickups. It uses an 80-gigabyte hard drive to store map data and has a DVR-style “time-lapse playback” that allows up to 20 minutes of content recording and replay from terrestrial and satellite radio stations.

 

If there’s one thing that heavy-duty off-road enthusiasts have wished for in powertrains, it’s a diesel engine for awesome low-end torque while rock crawling.

In 2008, Mopar debuted the Dodge Ram Diesel Power Wagon at Easter Jeep Safari in Moab, Utah, but that concept has remained just that because the Power Wagon’s integrated Warn winch blocks airflow to the 6.7-liter Cummins inline-six-cylinder’s turbo intercooler. The production Ram Power Wagon has a strong 5.7-liter Hemi V-8. Setting the Sierra All Terrain apart from both Power Wagon and the Raptor is its 6.6-liter Duramax V-8 diesel and six-speed Allison automatic transmission. The powertrain is virtually identical to the 397-horsepower, 765 pounds-feet of torque DMAX diesel offered in today’s GM HD pickups.

When the Duramax diesel is combined with the extra-strength off-road suspension, GMC says the Sierra All Terrain hangs onto its current towing ratings instead of sacrificing them for extra off-road capability. It’s estimated to be able to tow up to 13,000 pounds conventionally — about 3,000 pounds more than the gasoline-powered Raptor and Power Wagon pickups — and up to 15,600 pounds with a fifth wheel hitch.

Payload capacity is estimated at 2,959 pounds.

 

There’s little doubt that General Motors has missed an opportunity in off-road. While GM was trying to figure out what to do with the radioactive Hummer brand, Ford’s gamble on the go-fast F-150 SVT Raptor has paid huge dividends for enthusiasts and the company’s image. At the same time, a handsome styling update last year for the Ram 2500 Power Wagon brought new interest and popularity to Chrysler’s tough ground pounder.

The GMC Sierra All Terrain HD could be an excellent chance at redemption, but we wonder if there’s a market for a diesel-powered HD off-road halo truck that could probably cost more than $65,000.

At the 2009 SEMA expo in Las Vegas, Chevy showed a concept light-duty gas-powered supercharged Silverado ZR2 that also featured superior off-road capability over current production GM trucks, but nothing has been heard about that concept since. The GMC Sierra is GM’s second signal that it wants a piece of the off-road market. We’ve heard strong rumors of a revised V-8 gas engine for GM’s HD pickups possibly arriving before new sheet metal and interior. Putting a credible gas engine in the Sierra AT HD would reduce its price point to probably around the low $50,000s. At that point, it becomes a credible contender to the Raptor and Power Wagon.

According to Mike Tulemello, vehicle line director for GM fullsize trucks, a pickup like the All Terrain could be produced quickly by working with a second-stage manufacturer after rolling off the production line.

We hope GM takes a risk and enters unfamiliar terrain by producing a new HD model similar to the GMC Sierra All Terrain HD Concept. It’s already identified a new niche on the off-road map.

 Mike Levine is publisher of PickupTrucks.com.

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