Chevy makes a Wrangler/Raptor mashup of its midsize pickup
Today’s extreme off-roaders tend to fall into one of two categories: Amazing rock crawlers like the Jeep Wrangler with spectacular axle articulation and huge ground clearance, or high-speed desert racers like the Ford F-150 Raptor with extra-long suspension travel and soft suspensions capable of flying over jumps and absorbing bumps at speeds that would destroy a normal truck’s (or a rock-crawler’s) suspension. Chevy decided to build an in-betweener variant of Motor Trend’s two-time winning Truck of the Year by leveraging a key technology that helped make the 2014 Camaro Z/28 Motor Trend’s Best Drivers Car—Multimatic shocks.
Before we discuss these magic shocks let’s run down the roster of supporting hardware mods on this package, which is available in extended cab and crew-cab configurations with the 3.6-liter V-6 or the 2.8-liter turbodiesel four. The four-mode AutoTrac 4WD system (RWD, 4 auto, 4Hi, 4Lo) is upgraded to include Eaton electronically locking differentials on both axles. The rear can be locked in all four of the above modes, the front can only be locked in 4Lo after the rear axle is locked, bringing to nine the number of driveline modes available. Hill descent control is offered, and an off-road mode button invokes one of 30 different maps for tailoring the throttle response, shift strategy, and the ABS, traction and stability control systems to suit whatever conditions confront a ZR2.
Other functional improvements on the 2017 Colorado ZR2 include a suspension lift of 2.0 inches, a widening of the track by 3.5 inches, a swap to sturdier cast-iron lower front control arms, and fitment of 8.0 x 17-inch wheels wrapped in 31-inch Goodyear Duratrac off-road tires that afford exceptional traction. And to improve suspension articulation, the 1.5-inch diameter hollow front anti-roll bar is replaced by a softer 1.0-inch solid one. The axle ratio is unchanged at 3.42:1, as is the towing capacity of 5,000 pounds.
A unique front fascia greatly improves the truck’s approach angle and clearance to the front tires when they approach an obstacle on a rocky trail. It also incorporates a skid plate that protects the radiator and oil pan, with another further back shielding the transfer case. The rear bumper loses its corner steps, because these were getting pinched shut when dragged across rocks on the Rubicon trail. Structural rock rails protect the rocker panels and can support the weight of the truck if high-centered on a rock. Fender flares envelop the wider-spaced tires. An accessory rack can relocate the spare out of harm’s way to the cargo bed. Additional cosmetic changes include a shiny-black grille and performance hood with matte black insert, badges, interior sill plates, and embroidery on the headrests.
Now for those magic shocks. Shock absorbers work by plunging a piston through a tube filled with oil, and forcing the oil to flow through some sort of holes or channels that regulate how fast it can move. Usually these holes are in the piston, with flow through them being controlled by a series of metal discs that deflect as oil passes through them. Tuning these discs to provide precisely the right flow rate is a hugely time consuming pain in the posterior, and normal production tolerances can result in variation from the ideal flow rates of up to 15 percent.
Racing teams could never tolerate such inconsistency so in 2001 Multimatic Inc. of Markham, Ontario developed the Dynamic Suspensions Spool Valve and soon after Newman/Haas Racing teams using Multimatic DSSV dampers began winning Champ Car titles. Instead of deflecting discs, oil presses against another precision-machined spring-loaded piston or “spool” that moves inside a thin sleeve into which little ports are laser cut to extremely precise tolerances in a temperature-controlled environment. The shape of these ports is computer designed to regulate oil flow rates as the piston moves exposing more of the ports.
The 2014 Camaro Z/28 was the first “volume” production fitment of DSSV shocks to a road car, and those shocks placed two DSSVs in the piston of the shock, one to precisely control the rate of piston movement during jounce, the other to control rebound. The result is a car that keeps its tires pressed to a paved track under the most demanding conditions and affords a ride that is better than expected of a track weapon with such firm springs.
The Colorado ZR2’s duty cycle could not be more different, but the beauty of DSSV shocks is you can shape those orifices to deliver any force/displacement curve you like for any duty cycle. In this application, two DSSV valves like the ones in the Z/28 are relocated to a chamber next to the main shock tube. As the piston moves through the typical stroke experienced in on-road driving, it forces oil to flow out of that tube through a ring of orifices and into this chamber with the spool valves. More extreme suspension inputs of the type that typically only happen off road cause the piston to move past these orifices, at which point the oil is forced through a third jounce-control spool valve that’s located in the piston. This one is tuned more like a Baja racer’s shock. A third chamber contains the volume of nitrogen gas that accounts for the volume of the piston rod that plunges in and out of the space where the oil otherwise lives. Moving both the spool valves and this nitrogen charge out of the main tube allows for more suspension travel within the same shock absorber packaging space.
We got a ride in a Colorado ZR2 on an extreme off-road course set up near the 2016 Los Angeles auto show, and found the launches and landings off big jumps and bumps to be almost as Cadillac-smooth as what I once experienced riding with “Ironman” Ivan Stewart in a SCORE Baja racer. We’re promised that the on-road ride is smoother and more comfortable than that of the base Colorado, but had no opportunity to verify that. The course did offer some extreme articulation events, and a narrow “forest” to demonstrate the maneuverability of this truck that is about a foot narrower than a full-size truck, and hence can be threaded through tight trails like the Rubicon that would make a Raptor look like Christine killing Moochie Welch in that loading dock.
Expect to pay somewhere in the $40,000 range when the ZR2 hits the market in the spring of 2017.
More Multimatic Magic
- Turbulent flow. Flow through these spool valve orifices is naturally turbulent, which both reduces heat buildup in the oil and makes the shock much less dependent on oil viscosity. As a result, performance differs little during extreme use that might overheat and “fade” other shocks.
- No cavitation. Under extreme conditions, the oil can cavitate in a monotube shock of deflected-disc design, leaving vaporized oil in the tube. Preventing this typically requires using higher-pressure nitrogen gas, which can negatively affect ride quality. There’s little or no cavitation in a DSSV shock, so they can run lower pressures for better ride quality.
- Frequency tolerant. Typical disc-deflection shocks can behave quite differently under drastically different input frequencies, but DSSV shocks remain much truer to their design performance over a range of frequencies.
- Fast development. Once a chassis engineer determines the ideal force/displacement curve, a proprietary Multimatic computer program can design spool-valve orifices to deliver those characteristics precisely, cutting development time by 75 percent.