At the North American International Auto Show this year, the biggest buzz surrounded the largest concept there: GMC's Sierra All Terrain HD, an off-road-biased truck based on the 2011 Sierra HD platform. We sat down with Carl Zipfel, manager of GM's Advanced Truck Studio, to see if this dream vehicle can become a reality.
Why It Can
This concept was based on a crew-cab 2011 Sierra 2500HD. The idea was to build on the strengths of the HD chassis and powertrain and take the production model in other directions. The design group rallied around one specific sketch, executed as a full-size clay model. Parts were prototyped, and the vehicle was done in eight months. "We were able to do this one pretty fast because it's mostly production-based," Zipfel said. "It uses the production chassis, cab, and powertrain. All the design work focused on the off-road components and the front and rear clips of the vehicle."
It Doesn't Use A New Engine And Transmission
There were no major changes to the powertrain: It's the 397-horse, 6.6-liter Duramax turbodiesel, with the Allison 1000 six-speed automatic. The engineers and designers made the most significant changes to the suspension, body, and styling -- all of which, Zipfel explained, were focused on making a realistic, yet highly capable off-road version of the Sierra HD. Most of the parts were prototyped and built at the UAW shops within the Warren, Michigan, design center. These facilities include a mechanical assembly, fabrication shop, wood shop, model shop, and a plaster shop for the molds. The shops have all the tools needed to create a vehicle from the ground up. Parts don't even have to be sent out for chrome.
Body Mods Are Realistic
This layout is a crew cab 2500 that uses GM's shortest bed -- the 68-inch-long unit. This bed isn't available on the HD models; for the concept, this item started out as the short bed from a 1500, but by the time they were done, it was its own unique fiberglass bed. But we wouldn't be surprised if this third bed were eventually added to the options list for the three-quarter ton.
In addition, the crew cab's wheelbase and body were shortened by 5.1 and 9.2 inches, respectively, putting the wheels closer to the corners to improve the departure angle. Those changes make the truck viable on trails where the stock truck could get hung up. Another addition was a set of motorized side steps, taken from the Cadillac Escalade parts bin. While these are typically seen as luxury items, on off-road trucks they allow easy entry into lifted trucks, but won't scrape on rocks on the trail. In addition to the composite protection underneath, the All Terrain also has aluminum skidplates front and rear.
Even the styling, which is somewhat over the top, was done with function in mind. Its grille, which could be "a sneak peek into the future design vocabulary for GMC," was inspired by that of the Granite concept. A design cue from that compact concept is the three horizontal ports in the grille. The material is perforated; that, plus the port design, means the grille allows more air into the engine bay. That increased airflow can be especially important when towing uphill on a summer day -- not an unusual scenario. Another sneak peek is the concept's Iridium Metallic paint. Per Zipfel, this color is coming in the future as a GMC exclusive.
Suspension Changes Are Smart, And Not Too Outlandish
What most dramatically affects the function of this vehicle are the suspension changes, all of which are focused on off-road performance without sacrificing day-to-day driveability. The All Terrain has 11.8 inches of ground clearance, compared with a four-wheel-drive 2500HD crew cab's 8.2 inches. Because of where the wheels are located on the vehicle, as well as cutouts on the fender flares, the total suspension lift needed to be only 3 inches to clear the 35-inch tires, which are on custom 20-inch wheels made from raw billet. Changing the wheel offset widened the track for better stability.
The modified suspension includes new versions of the upper and lower control arms, done in machined aluminum; an electronically disconnecting front anti-roll bar for more off-road travel; and the use of jounce shocks front and rear. One of the few things GMC got from an outside source was the shocks for the All Terrain, modified versions of off-the-shelf units from Fox Racing Shox. These shocks accommodate the change in geometry, increase travel, and have the durability needed for hard driving off-road.
Why GMC Should
Right now, there are two off-road-specific trucks on the market: the Raptor and the Power Wagon. Yes, Chevrolet offers the Z71 version of its Silverado and Colorado, but those are watered-down mass-production option packages, whereas the Raptor and Power Wagon are highly specialized models. A production version of the All Terrain would give GM a competitor in this relatively new niche category, and it would be the only one with a diesel.
That it has a crew cab and a short bed puts it more in line with the Power Wagon, but even with that, Zipfel says the All Terrain is a different beast. "We certainly weren't trying to do a Raptor or a Power Wagon. We did our own formula -- the way we saw it correctly fitting into the GMC idea of being 'Professional Grade' -- and we wanted to offer something that neither the Raptor or Power Wagon has.
Our off-roader combines the diesel with the heavy-duty chassis and a lot of off-road-ready parts. The Raptor is more of a high-speed desert runner, so it has similar suspension [Fox shocks], though the geometry is somewhat different from ours. But it doesn't have a diesel and it uses a light-duty chassis.
"The Power Wagon is a heavy-duty chassis, but doesn't offer the diesel. We did it our own way, knowing that diesels really are the off-roader's powertrain of choice because of the torque. It's great for off-road, plus heavy-duty towing and hauling; the diesel is a super powertrain for that. We see a different customer for this as opposed to the Power Wagon or Raptor. This is a professional person who on weekends needs to haul a boat or a large trailer, and maybe get into areas that are a little more treacherous to traverse. He wants something premium with HD towing/hauling capability."
Zipfel is a truck guy who has focused on GMC for many years and has done work with Hummer (see sidebar). He would love to see the All Terrain go into production. He feels that just about everything but the concept's LED lighting could make it into production.
Zipfel explained that with concepts like this, there are always internal studies and discussions about whether they would be viable production models, and if so, how it could be done. Two choices would
be to offer the parts through GM's SPO accessory lines or to build the whole truck on the line with the rest of the HD line.
Will they build it? We hope so.
Carl Zipfel, long-time manager of GM's Advanced Truck Studio, has been responsible for standout concept vehicles.
2000 GMC Terradyne
This concept was designed as a tough, high-tech work truck, with an industrial bias. It was built from durable materials and shown with an engine-driven 5000-watt generator. The concept was powered by an early version of the Duramax 6.6-liter turbodiesel.
2001 GMC Terracross
Terracross (or Terradyne: the Sequel), was an SUT that used similar styling to the Terradyne, and featured a three-panel sliding-glass roof and an early version of the Midgate. This all-wheel-drive concept used GM's 3.4-liter V-6.
2002 GMC Terra4
The third in the Terra series, the Terra4 made use of GM's Quadrasteer four-wheel steering, and was a parallel hybrid truck that used the 5.3-liter V-8 Vortec and a 4.8-kW motor. The 4 in the name was because of the concept's four-wheel drive, four-wheel steering, four doors, and four ways to access the cargo area.
2008 Hummer HX
Had this concept made it to production, it might have saved Hummer. The HX was shorter than the H3, with a 304-horse direct-injected 3.6-liter V-6. It had a removable roof, fenders, and doors, Fox shocks, and awesome approach and departure angles. This one would've had Jeep shaking in its boots.
| GMC Sierra All Terrain HD Concept |
| POWERTRAIN |
| Drivetrain layout || Front engine, 4WD |
| Engine type || 90-deg V-8 turbodiesel, iron block/aluminum heads |
| Bore x stroke || 4.06 x 3.90 in |
| Displacement || 403 ci/6.6L |
| Compression ratio || 16.0:1 |
| Valve gear || OHV, 4 valves/cyl |
| SAE horsepower || 397 hp @ 3000 rpm |
| SAE torque || 765 lb-ft @ 1600 rpm |
| Transmission type || Allison 1000 6-speed automatic |
| 1st || 3.10:1 |
| 2nd || 1.81:1 |
| 3rd || 1.41:1 |
| 4th || 1.00:1 |
| 5th || 0.71:1 |
| 6th || 0.61:1 |
| Reverse || 4.49:1 |
| Axle ratio || 3.73:1 |
| Final drive ratio || 2.28:1 |
| DIMENSIONS/CAPACITIES |
| Wheelbase || 148.6 in |
| Length x width x height || 230.9 x 83.0 x 81.8 in |
| Track, f/r || 73.0/73.0 in |
| Approach/departure angle || 39.0/31.0 deg |
| Ground clearance || 11.8 in |
| Payload capacity || 2700 lb |
| Towing capacity || 15,600 lb |
| Seating capacity || 5 |
| Headroom, f/r || 41.2/40.5 in (est)* |
| Legroom, f/r || 41.3/39.0 in (est)* |
| Shoulder room, f/r || 65.2/65.1 in (est)* |
| Bed length || 68.0 in |
| CHASSIS |
| Construction || Ladder frame |
| Suspension, f/r || Independent, control arms, torsion bars/live axle, leaf springs |
| Steering type || Power assist recirculating ball |
| Brakes, f/r || 14.0-in disc/14.0-in disc, ABS |
| Wheels || 9.5x20-in aluminum alloy |
| Tires || BFGoodrich Mud-Terrain T/A KM2 325/60R20 121Q |
| *based on production GMC Sierra Crew Cab |