Engineering the 2020 GMC Sierra HD

Tim Herrick executive chief engineer, GM full-size pickup trucks, and the tailgate that other OEMs wish they had. (Image: GSV)

There has probably been no more propitious time for GMC to exist than right now. Truck and SUV sales are ever-increasing as is the amount of money that people are willing to spend on those vehicles. So as the “premium” brand in the GM collection, and as the only company that provides trucks and SUVs and nothing else (i.e., no sedans to put drag on its momentum), GMC is in an incredibly good spot.

And GMC personnel have done a clever thing in creating premium subsets within the whole set in the form of Denali and AT4 packages. Denali has had a longer existence than AT4, which just launched for model year ’19, and the Denali take rate is 29 percent of all GMC vehicles sold. What’s more, the GMC accountants have calculated that if Denali was a brand onto itself it would have the second-highest average transaction price in the industry; at ~$54,000, it would be second only to Mercedes. At this early point they’ve determined that the AT4 buyer is eight years younger than the average GMC customer (as well as having more household income), so AT4 helps maintain the possibility of customers with statistically more longevity.

Why the AT4?

Matt Noone, GMC Design director, explains that the development of the AT4 was driven by potential customers who said that they weren’t interested in a Denali, but that they still wanted a premium truck, something that provided the materials and technology of a Denali, but has more of a rugged personality. “The AT4,” Noone says, helps drive us back to the core of GMC: Capability, durability and usability.” From a pure styling standpoint, where the Denali has the brightness of chrome, the AT4 has the seriousness of dark, monochromatic trim.

Every Sierra HD with a 6.6-liter diesel V8 and dual rear wheels can tow 30,000 pounds. The regular cab 3500HD is engineered to handle 35,500. (Image: GMC)

When it comes to heavy-duty (HD) crew cab vehicles since 2015 GMC has found that if you look at the customer distribution there is something of a wave form, with value trims being a crest that flows down to the trough of mid-trims and then rises to the premium trims. Which also goes to the point of Denali and AT4, but there are the lower trims that the company has on offer for its Sierra HD pickups.

Because They Tow

While there could be a number of reasons why someone buys an HD pickup, the biggest number is for towing: 93%. What’s more, 50% of the HD drivers tow more than 8,000 pounds.

So GMC engineers set about to create a vehicle that could tow 35,500 pounds, a regular cab 3500HD with dual rear wheels and a diesel engine. (All of the diesel Sierra HDs with dual rear wheels are capable of towing more than 30,000 pounds.) That particular configuration also has a GCWR of 43,500 pounds. (By way of context know that the comparable truck of the previous generation has a maximum trailering capability of 23,300 pounds and a 31,300-pound GCWR.)

Design director Matt Noone says that he and his team worked with Engineering to make sure that whether the bed was full of logs or empty the box would appear to be on the same plane. And speaking to other aspects of the HD Sierra compared to the design of the 1500, he says, “Everything is beefed up,” adding, “The HD customer doesn’t want it to look like a light-duty. For the heavy-duty customer, a light-duty is a grocery-getter.” (Image: GMC)

The Engines

A word about that engine. It is a Duramax 6.6-liter V8 turbodiesel. This engine first appeared on the 2017 Sierra HD. It has a cast-iron block. It has a cast aluminum head. The engine features overhead valves and four valves per cylinder. It has a 28-inch cooling fan and a dual-air intake system. Which goes to the point that the engine needs to breathe. Robustly.

The diesel produces 445 hp at 2,800 rpm. But to get to that point of 35,500 pounds of towing the engine produces 910 lb-ft of torque at 1,600 rpm.

The diesel is mated to an Allison 10L1000 10-speed automatic transmission, the first ever of its type.

The base engine for the 2020 GMC HD is a 6.6-liter V8 gas engine that also features a cast-iron block but it has nodular iron main caps. The cylinder head is cast aluminum. It also has an overhead valve configuration, but it has two valves per cylinder and variable valve timing. It produces 401 hp at 5,200 rpm and generates 464 lb-ft of torque at 4,000 rpm.

The gas engine is mated to a Hydra-Matic 6L90 six-speed automatic

While the diesel engine certainly gains much in the way of interest due to its capability, according to Tim Herrick, executive chief engineer for the truck, the gas engine is purpose-built and is used only in GM HD trucks. He points out that it provides 11 percent more horsepower and 18 percent more towing capability than the engine in the previous generation HD truck.

The Sierra HD offers 15 camera views. If there is a trailer on the back the system makes it appear as though the trailer is transparent so the driver can see what is behind the vehicle. (Image: GMC)

What’s more, he says that the engine provides “capability at all altitudes.” Herrick explains, with a bit of exaggeration, “You can take a Sierra with a gas engine anywhere in the galaxy and I guarantee it will tow the numbers I say it can tow.” He explains that other OEMs indicate that for every 1,000 feet above sea level there is a 2- to 3% reduction in capability. Depending on the configuration and the towing setup (i.e., conventional or 5^th wheel/gooseneck), the towing capacity of a gas-powered Sierra HD ranges from 14,500 pounds to 17,400 pounds. (Odds are Star-Lord won’t be rolling in a Sierra in the next Guardians of the Galaxy film, however.)

Why No Solid Front Axle?

Apparently the fact that the Sierra HD has an independent front suspension rather than a solid axle is a bit of a burr under the saddle (a metaphor used because one of the things that the truck is used for is towing horse trailers that are approximately the size of a stable).

Herrick: “Some people are going to tell you you need a solid front axle on a heavy-duty truck or its not durable. I’m going to tell you it is a bunch of baloney. I can use a stronger word, but. . . “

He admits that they thought about putting a solid axle on the truck but then bought heavy duties from Ram and Ford—with solid front axles—on the GM durability schedule at the GM Milford Proving Grounds and, well, Herrick says that they didn’t do so well. According to Herrick, the use of the independent front suspension is particularly good regarding ride shake and comfort while trailering. And, he adds, durability.

As previously mentioned, there is a lot of towing that occurs with an HD pickup.

Herrick says that when they were developing the vehicle architecture they surveyed some 7,000 people. (He points out that they’re the only OEM that belongs to both the RV Industry Association and the National Association of Trailer Manufacturers, so they have a good sense of what matters on the ground to people in the trailering community.) Then they zeroed in on about 1,000 people to ask about towing. Herrick says: “Fifty-seven percent told us that towing is stressful. Do you know what the other 43 percent did? [pause for a beat] They lied.”

Deploying Cameras

Which gets to the point of what is really significant about the engineering of the Sierra HD. Granted that it is structurally sound and more than up to it vis-à-vis propulsion. But a main area of focus was on the deployment of technology that allows drivers to have a better sense of where they—their truck and whatever they’ve attached to the back—are in space.

The MultiPro tailgate is available on the Sierra HD. So as a bit of a dig at the competitors, the team loaded a flatbed trailer with the tailgates of the competition to demonstrate the ease of towing some 30,000 pounds. (Image: GMC)

So they’ve deployed a system that provides 15 different camera views (there are a tailgate camera, side cameras and rear camera (with this last-named feeding into an available dual-function rearview mirror, which is either a standard mirror or uses the camera input for the display)) such that the trailer—up to 32 feet in length—seems to be “invisible,” such that in the screen in the center stack shows what’s behind the trailer.

Through visibility comes more trailering confidence—for the 57% and the 43%.

And, yes, the Sierra HD models come with the six-function MultiPro tailgate. Which is also rather significant, given that Herrick says of what it means: “You only get a couple of these in your life as a chief engineer.”