Some folks will tell you that a solid axle is required for heavy-duty off-roaders. GM’s engineers will tell you that’s wrong.
The heavy-duty off-road pickup segment is suddenly one of the industry’s most competitive. Ford, Ram, and General Motors all sell multiple trucks that are meant to tow big loads and tackle tough trails on the same day. The Chevy Silverado HD ZR2 and GMC Sierra HD AT4X are the latest entries, and they take a unique approach with Multimatic DSSV dampers and independent front suspension. You’re more likely to find that combo on a race car than any other 3/4-ton pickup, so I wanted to talk with GM’s engineering group manager Tim Demetrio to learn how they did it.
GM has stuck with IFS on its HD pickup offerings for nearly two decades. Others use solid axles for simplicity and durability, some will argue, but Chevy and GMC see things differently. When I asked Demetrio why IFS is the right choice for a truck like the Silverado HD ZR2, he confirmed: It’s about ride and traction.
Chevrolet
For sure, trucks with solid axles often relay more road info to the driver when it’s not necessarily needed. You could argue that GM was ahead of the game by valuing comfort on its hardest working models all those years ago. And Demetrio argues that because the Silverado HD’s suspension is already built to work, it was naturally tough enough for the off-road ZR2 halo model.
“The cool thing about starting with a heavy-duty platform is all the components are already very, very well-suited for what we throw at them in the desert,” Demetrio said. “Beefy components are required to hit the towing and payload figures that the base HD starts with, and it’s a great platform to build with so we really didn’t have to strengthen much up there. They already have cast-iron control arms, we have big, beefy front suspension joints, and the torsion bars are meant to handle plow prep packages and lots of load. Honestly, what you throw at it in the off-road space is kind of less severe than what a lot of users will do in the heavy-duty space already.”
It makes sense that if a truck is built to accept a snow plow up front, it can probably handle bumps at speed. That makes the Silverado HD a better base for a hardcore four-wheeling trim than you might think. Plus, IFS is already preferred for desert running by everyone, including race teams; it’s usually just used in lighter applications.
“As far as off-roading goes, you look at all the trucks out there that are very high performance—you know, you look at a trophy truck and it has independent front suspension,” Demetrio said. “All the people that say you need a solid front axle to go off-roading are living back in the ‘70s, in the Jeep days.”
We’ve only seen those Multimatic DSSV dampers on smaller vehicles so far. The tech was actually first deployed on open-wheel cars, helping the Newman-Haas team win seven of 19 CART races in 2002. Multimatic has since provided its DSSV units to multiple automakers, including Chevy several times before with the Camaro ZL1, Colorado ZR2, and light-duty Silverado ZR2. Turns out, they’re easily scalable, requiring little modification to work on each rig. That’s a key reason manufacturers love ’em, along with their unfading performance.
“With the Multimatics, they have a huge tuning bandwidth. That’s kind of the secret sauce and that’s why we keep going back to the DSSV,” Demetrio told me. “With our position sensitive zones—you have a normal zone, a rebound zone, and a jounce zone—you can tune each of those individually, so it gives you this huge bandwidth of range you can make the damping forces operate in.
“When you look at something like a high-performance midsize off-road truck versus our heavy-duty trucks, the damping forces required aren’t drastically different, even with the mass being different. With the HD, you expect a little more supple ride, a little softer, and a little more movement. Whereas you look at the Colorado and Canyon, they’re a much firmer, sportier ride. Look into the damper forces, though, and they’re pretty close. The HD still has more force, but it’s well within the bandwidth of those DSSVs and the operating range of the internals.”
“The hardware is different,” Demetrio explained. “That’s driven a lot by packaging. You look at the HD and you have a giant half-shaft going through there; it’s a completely different suspension setup up front than our light-duty and midsize trucks. So the packaging of the reservoirs is done differently and where the spool valves are located in the damper, but the piston hardware between all three trucks is the same size. We have a few differences in the sealing technologies in them, but overall, I would say at the high level they have 75% of the same componentry with just some differences for packaging.”
Chevrolet
Demetrio mentioned that “secret sauce” a little earlier in our convo. A lot of folks write trucks off as being too simple, or too big to perform, or what have you. And while some gripes are warranted—without a doubt—it’s wrong to classify rigs like these as basic. Just because they’re body on frame and ride on tall tires doesn’t mean they’re one-trick ponies, far from it.
That’s how our talk ended, discussing the complexities of engineering a high-performance off-road HD model. Demetrio closed by saying:
“My group deals with all the performance variants that General Motors does. In addition to the ZR2s and AT4Xs, we deal with the Blackwings. I will tell you that on-road performance, as far as vehicle manufacturing goes, is significantly easier than what you do in the off-road space. A paved race course doesn’t change every time you run it. You can design for ones and they generally work at all of them the same. Whereas in the off-road space, when you design for desert running, you have to make compromises in what you want to excel at rock crawling. The off-road space is so much more complex. Trucks are way more complex than race cars.”
That’s not coming from some bro on the internet; it’s straight from the guy who helps develop some of the industry’s greatest performance vehicles. These trucks are built to do it all, whether on or off the road. Now’s an exciting time to be a four-wheeling fanatic, that much is for sure.
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