CHELSEA, Mich. -- Chunky granite boulders stack up as one of many stair-stepping barriers to our four-wheeling progress while steering a 2013 Jeep Grand Cherokee Trailhawk special edition sport utility vehicle on a definitive off-road track for Jeep at Chrysler's vast vehicle test facility in Chelsea, Mich.
Confronted by the bumpy tangle of rocks, any driver might prudently assume that the best way to proceed beyond this barrier would be to find some path that skirts it, but for our experiment we must crawl over the boulders because the objective of this excursion is to test the off-road prowess of Jeep's ultimate four-wheel-drive (4WD) SUV.
Sturdy Grand Cherokee represents the original sport-utility vehicle tracing back in Jeep history to 1963 and the Wagoneer, with innovations like the Quadra-Trac automatic full-time four-wheel-drive (4WD) system and a limited slip differential, introduced in 1973, and the watershed design of 1984 for the first unibody four-door SUV.
The nameplate of Grand Cherokee emerged in 1992 on a new wagon which demonstrated that a SUV could conquer rugged challenges of the off-road world and still transport riders in comfort due to cushy cabin appointments.
A larger version appeared in 1999 with a sleek shell and a luxury-lined cabin plus mechanical systems aboard which raised the bar for SUV performance, while new schemes for Grand Cherokee in 2005 and 2011 established even higher SUV benchmarks.
Now Grand Cherokee for 2013 constitutes a diverse array of models and culminates with the most capable dirt-dog 4WD off-road version labeled Trailhawk.
The special edition Grand Cherokee Trailhawk offers a choice of two Jeep powertrains (3.6-liter V6 or 5.7-liter V8) and installs all of the important hardware needed for traversing difficult trails with standard Jeep Selec-Terrain system, the Quadra-Lift air suspension, 18-inch Goodyear Silent Armor off-road tires with Kevlar reinforcement plus rock rail and underbody protection.
Jeep's Quadra-Lift air suspension system has five driver-selectable height settings and can deliver a maximum of 4.1 inches of lift.
Jeep's Selec-Terrain traction control system, which works with a Quadra-Trac II (for V6) or Quadra-Drive II (for V8) 4WD system, allows a driver to dial in one of five terrain settings (Normal, Sport, Snow, Sand/Mud, Rock), then the system tailors the vehicle's traction performance to fit the type of terrain covered through modulation of powertrain response, transmission gear selections, and electronic controls like electronic stability control (ESC).
To scale the Chelsea boulders we twirl the Selec-Terrain dial and select Rock. Subsequently, we feel the Quadra-Lift air suspension system elevate Grand Cherokee's suspension to max height of 10.7 inches while the transfer case, differentials and throttle coordinate to provide plenty of low-speed torque to power crawl over those rocks.
Later in a soppy stretch of mud encountered on the off-road course, we turn the dial to Sand/Mud. Next, we feel a power surge in the pedal as you need lots of torque to keep the wheels rolling through tire-sucking mud.
But when we switch to Snow mode, we get less power in the throttle because big torque only spins wheels on slippery surfaces.
The full-time 4WD systems available for Trailhawk include Jeep's Quadra-Trac II system, which brings a two-speed electronic transfer case for full-time active 4WD operation and locked 4WD low range, and the automatic Quadra-Drive II system with rear ELSD (electronic limited slip differentials) to deliver infinite torque management at each of the four wheels.
Standard engine for Trailhawk is the flexible-fuel 3.6-liter dual-cam Pentastar V6 with an aluminum cylinder block and VVT (variable valve timing) controls. It delivers 290 hp at 6400 rpm with 260 lb-ft of torque at 4800 rpm.
Optional engine is a 5.7-liter HEMI V8 with VVT and MDS (multi-displacement system) to conserve fuel by clipping cylinders when boosted power is not needed. The HEMI scores 360 hp at 5150 rpm with 390 lb-ft of torque at 4250 rpm.
A five-speed electronic automatic transmission (W5A580) applies to the 3.6-liter V6 engine, while a six-speed electronic automatic (65RFE) goes with that torque-monster 5.7-liter V8.
The Trailhawk special edition is easily identified due to added exterior armor such as red tow hooks and the rock rails pinned below side rocker panels.
Up front, Trailhawk shows a matte-finished black and red stripe across the hood and black bezels surrounding headlamps, with the wheels, exterior mirrors and tailgate tinted to dark gray.
Trailhawk exterior paint choices are limited to Bright White, Brilliant Black, Mineral Gray, Winter Chill, Maximum Steel and Deep Cherry Red.
In a cushy cabin, the front bucket seats are clad in a leather-suede combo stitched with contrasting red thread and crowned by the Trailhawk emblem on seatbacks.
Jeep outfits all Grand Cherokee editions with a commendable array of standard safety systems. The gear extends to side-impact air bags in the two front seats with active head restraints and curtain-style side air bags for two rows of seats, plus electronic vehicle controls such as ABS (anti-lock brake system), BTCS (brake traction control system), ESC (electronic stability control), ERM (electronic roll mitigation), TSC (trailer sway control), HSA (hill start assist), HDC (hill descent control), even TPMS (tire pressure monitoring system).
Jeep sets price points for 2013 Grand Cherokee models in a broad spectrum but beginning as low as $27,495 for Laredo trim with 2WD traction.