Basic Off-road Features of the Vehicle

As the third generation of the Grand Cherokee series of Jeep vehicles, the 2005+ Grand Cherokee (designated the "WK") represents a vehicle with driver comfort and off-road capability that is much improved from previous generations.  As our focus here is off-road performance, the primary new vehicle features are the new Quadra-Drive II (QDII) drive train, and independent front suspension (IFS), which replaces the solid axle configuration of previous generations of Grand Cherokees.  (Besides the QDII the new Grand Cherokees are available with two other drive train configurations which are not discussed herein:  Quadratrac I and Quadratrac II).  Most enthusiasts feel the remarkable increased off-road performance that QDII provides in terms of traction are at least in part offset by the decreased wheel travel (articulation) that is characteristic of the IFS.  For most off-road circumstances this combination (QDII and IFS) yields performance that at least equals a comparatively-equipped, non-QDII vehicle with a solid front axle.  Though it is not represented as such by Daimler-Chrysler (DC), the QDII drive train does in fact fully lockup both front and rear axles when conditions warrant, just as would be the case with a vehicle equipped with ARBs or similar differential-locking mechanisms.

There are several standard and optional skid plates available as OEM components of the Grand Cherokee.  For off-road travel it is important to purchase a WK with, or have installed after purchase, all the skid plates available from DC as these are cost-effective protection for major mechanical components that can potentially suffer expensive and debilitating damage during off-road travel.  These components typically include the gas tank, front differential and transfer case.  More will be said in this regard as part of the following discussion.

Specialized Equipment for Off-road Travel

In its OEM configuration, even if equipped with QDII and the full complement of optional skid plates, the 2005 Grand Cherokee has one major limitation when it comes to traversing all but “moderate” off-road trails:  it has a lack of adequate ground clearance compared to its relatively long (109+ inch) wheelbase.  The good news is that this drawback is relatively easy—but costly--to correct with a lift kit and larger-diameter tires.  However, changes such as these alter the handling characteristics of the vehicle and care must be taken to correct or offset such changes in order to not have a potentially unsafe vehicle, especially during emergency situations.

Lift kits

Lift kits are generally of two types.  The least expensive are kits that simply elevate the body above the existing suspension system.  These kits are sometimes referred to as “budget boosts” (BB) and for the WK generally consist of high-density rubber or plastic “donuts” that are placed above or below the rear coil spring, and brackets and perhaps “donuts” that are added above or below the front suspension.  These systems are generally designed for about 2 to 3-inches of vehicle lift and result in varying degrees of changes in the vehicles ride and handling characteristics.   The addition of tires as large as 265 x 70 will add another inch or so to vehicle clearance and greatly improve off-road performance. For several months we had a Daystar/Skyjacker 2-inch lift kit that was relatively easy to install, provide greatly increased off-road capability, and, though it did result in a somewhat harsher ride, provided relatively stable and comfortable on-road behavior.

The second type of lift kit is more expensive and complex, and involves replacing/modifying suspension-system components in order to elevate the vehicles.  In most cases this type of kit should be installed by a qualified technician.  Like the BB these kits result in varying degrees of changes to the vehicles ride and handling, but typically result in 3-4 inches of vehicle lift and will generally allow tires as large as 285 x 70. We have used the Superlift 4-inch kit for a number of years and found it to perform extremely well off road and provide amazing on-road ride and handling; we have used both 285 and 305 tires with this configuration, and recommend the 285 unless one is willing to deal with some tire-rubbing issues.

Tires

Depending on the type and amount of lift kit used one can go with much larger diameter tires.  The advantages of larger tires are the resultant increase in ground clearance, the contact area of the tread to the ground, and the availability of tires with higher ratings and more aggressive tread patterns.  Related disadvantages are an increase in center of gravity (decrease in stability),  in effect a change in gear ratio and thus reductions in vehicle power and changes in transmission-shifting points, and increased tendency to slip in certain conditions such as wet or slick roads, due in part to the larger surface area and the many times more aggressive tread design.

Skid plates and other exterior protection

Assuming the vehicle has all the standard and optional OEM skid plates there are at least four other body areas that require additional protection from the rigors of severe offloading.  Two of the most important but often overlooked areas are the rear fascia and the area behind the front differential and in front of the transfer case.  Due to the longer overhang (distance from the centerline of the tires and projection of the vehicles body) in the rear and its inability (compared to the front end) to be maneuvered, this area is very vulnerable to scraping or breakage as the front of the vehicle raises up in approaching a steeply inclined obstacle or the vehicle comes off an obstacle such as a steep ledge, fallen tree or large boulder. If one examines the underside of their WK it is clear that there is a large area directly behind the front tires where the catalytic converters (yes, there are two) and exhaust component hang down, making them very vulnerable to off-road damage (which is very expensive to repair). 4XGuard offers the Rear Guard HC and the Belly Guard HC that provide protection for these two areas.

The other areas that can benefit from protection are the front end and rocker panel.  On the Jeep Grand Cherokee parts of the steering assembly and cooling-system components can be damaged due to an encounter with a large rock, tree stump or the like.  An aftermarket skid plate, such as the Front Guard HC by 4xGuard, is the best protection of this area of vulnerability.  Similarly, the rocker panel can be easily damaged should the vehicle (with its relatively long wheelbase) come off a large obstacle.  Currently (2006) “rock rails” are available from Mopar, Rocky Road and 4xGuard.  The Mopar and Rocky Road products mount below the rocker-panel area and therefore reduce the already minimal ground clearance by several inches, while the 4xGuard product decreases ground clearance by less than ½ inch.

Safety: Dealing with lift kits and larger tires

WK with stock suspension and 265 tires , 2-inch BB and 265 tires, and 4-inch Superlift and 285 tires

There is a saying among off-road enthusiasts that “if you go up you need to go out”, meaning that if one raises the vehicle--and thus the center of gravity of the vehicle--you should increases the vehicles track width (side-to-side distance between tires) to retain as much stability as possible.  Sometimes this means wider tires, sometimes wider wheels, sometimes wheels with a different backspacing, and sometimes a combination of these modifications.  For example, if one raises the vehicle 3 inches, increases the backspacing of the wheels by an inch on each side, and uses tires with widths several inches greater than stock, then you have done a relatively good job of addressing the increase in center of gravity.  A well-designed lift kit--such as that by Superlift--also addresses this issue by incorporation of properly rated suspension springs and valved shock-absorbers.  

On-road Driving—Towing

For years we have enjoyed owning a travel trailer. In fact it was the need for a V8 to pull our 1974 Award to Alaska that first brought us to the Grand Cherokee. Though we loved our first WK, a 2001 molel with the 4.7 liter V8, we felt a 5.7 liter "hemi" would do a much better job of pulling our new 28 ft, 5,500 lb (dry) travel trailer, a 2007 Flagstaff. For us it has worked out very well as this setup has served us very well for over 4 years. In May 2009 our trusty 2005 model was replaced with a 2008 Overland with a CRD (Common Rail Diesel) engine. I had heard good things about this Mercedes engine, with is turbo charger, and felt it would improve trailer towing (especially over our high mountain passes) as well as enhance off-road capabilities with its standard "hill-descent" mode and better compression. That indeed proved to be the case and we are very pleased with both the vehicle and with its diesel engine. As we evolved from the 2005 Hemi to the 2008 CRD the following are our observations:

Handling. Handling a trailer of this size with a relatively short wheelbased SUV was an initial concern for safety reasons, but this concern was ill-founded. The only handling issue we have ever experienced is occasional premature activation of the Electronic Stability Control during fairly sharp turns on steep downhill inclines. Of course we have a weight distributing/equalizing hitch and electronic brake control that are a must for a trailer of this size. The addition of an EGR Module in about 2007 greatly reduced premature engagement of the ESP system.

Performance. Our second major concern was the ability of the 2005, even with the 5.7, to pull our large trailer over the high mountain passes, where horsepower/torque are significantly diminished. Of course our very large (34 in) tires exacerbated this issue. We found that the 2005 WK did make it over the passes, but it was frequently in first gear, which is slow going, the last mile or so. Though a minor embarrassment, it was not a significant issue. Our 2008, on th eother hand, has obviously much less trouble over the high passes, never droping into first gear and seldom into second gear. It is marvelous.

When pulling such a relatively large trailer a related issue is typically cooling. During the time we had our 2005 we had two power steering units, which drive the WK's hydraulic fan, fail before we eventually determined the we need to keep the WK at a maximum of 4,000 rpm's or the vehicle will overheat. Though we added an electronic fan to supplement the hydraulic fan, it did not significantly help. Adhering to the 4,000 rpm limitation seemed to be the best solution and we had no further problems with cooling. Our 2008 model has not experienced any cooling issues, though it does not typically run at such high rpm's since it can maintain speed up the steep grades without dropping into lower gears.

Off-road Driving Techniques

It is not possible to convey in written form all the nuances of driving off road.  It is a typically “practice makes perfect” sort of thing.  However, there are some key considerations when driving off road that should be kept in mind regardless of the situation:

Speed.  In general the slower the speed the better.  There are some rare occasions, such as a long segment of deep mud, where momentum is the key to conquering the obstacle.  But many times too much speed causes tires to leave contract with the terrain, increases the potential of a loss of control of the vehicle, or causes the vehicle to be tossed about such that critical steering and braking loose their effectiveness. Sand and slick surfaces often due require extra momentum to traverse, but again care must be exercised in order to avoid an uncontrolled and potentially unsafe situation.

Choosing the proper “line”.  Essentially any difficult off-road situation presents the driver with a decision regarding how best to direct the vehicle in order to be successful it negotiating the obstacle.  This amounts to choosing a good “line”.  Though practice gives one a leg up in such decision-making, even the most experienced off-roaders will ask for spotting assistance in some cases.  A “spotter” may be ones spouse or a fellow trail-rider who watches from outside the vehicle for proper placement of wheels in order to best negotiate the obstacle; the ability to be a good spotter, like that of a good driver, takes practice and understanding of vehicle capabilities and the complex interaction/dynamics of a vehicle negotiating a variable terrain.   One should not regard such assistance as a negative reflection on their driving ability, but rather doing the right thing to insure a safe and successful off-road experience.

Steep inclines. 

A steep cline generally results in poorer visibility of the road surface in front of the vehicle and transfer of weight from the front tires to the rear tires, both of which can make for increased difficulty in negotiating the obstacle safely.  In most off-road situations the best way to successfully climb a steep hill is not with excessive power or speed.  As previously stated such techniques generally result in the vehicle bouncing or otherwise loose contract with the terrain, which obviously cause loss of traction and vehicle control.  In some cases such a method puts the vehicle at risk of rolling over as it gets cross ways of the hill or, in the case of very steep inclines, flipping over backwards.  The solution to these circumstances is a slow and controlled ascent, perhaps with the help of a spotter.

Steep declines.

Like inclines, a steep decline generally presents a situation of less visibility of the terrain and the need to control vehicle speed.  With the redistribution of weight now to the front wheels care must be taken to avoid any bouncing that can result in the front end (where major mechanical components are located) contracting an unseen rock or other obstacle, and the possibility of the rear of the vehicle sliding sideways and thus increased the potential for a rollover.  The vehicle should always be in the lowest gear and in low range to achieve maximum control of vehicle speed by engine compression.  Should one need to use the brake it should be done gently and carefully so as not to lockup the rear wheels, which especially in wet or slippery conditions will increase the potential for the vehicle to slip sideways.

Deep water. 

Jeep vehicles are designed to safely negotiate up to 19 inches of water at 45 mph; this is part of its “Trail Rated” designation.  Admitedly this is largely a marketing thing and of little practical value in the field. While four wheeling traversing deep water not only brings with it uncertainty of actual depth, but also the potential to encounter unseen and dangerous obstacles, such as submerged tree limbs or large rocks.  Obviously speed is unwise under such conditions, if for no other reason than the resulting waves and splashing increase the potential for water getting into engine and other components, which either many cause the engine to stall or cause damage to vehicle components.

Mud and slick surfaces. 

There is perhaps no off-road situation that deserves more care and skill to safely negotiate than traversing a large mud hole, snowy/icy inclined trail, or rain-dampened series of large rocks.  Such obstacles present all of the adverse conditions a driver might be confronted with off road:

• Inability to control vehicle direction and speed.
• Unseen hazards
• Poor traction
• Poor visibility

Thus it is important to address these conditions with common sense and skillful driving techniques.  Frequently there is need under these conditions for more momentum due to the decreased traction, but unseen hazards and the potential for loosing control of the vehicle pose the potential for the vehicle to become stuck, damaged or both.  In many cases one’s common sense, awareness of vehicle capabilities and driver skill dictate the obstacle should not be attempted. 

Sand. The best ingredients for negotiating sand are non-aggressive tires, low tire pressure, steady power.  Choice of proper transmission and transfer-case gearing is frequently critical to maintain sufficient power to overcome the friction of the sand while not spinning the tires or going too fast.

Rock crawling. Though one certainly encounters steep hills or mud holes on occasion, by far the most common four-wheeling obstacle is negotiating boulders on the trail that appear to have the potential to strike the underside of the vehicle if driven over. Obviously this is not the time for excessive throttle. Here again tire placement is critical and a "spotter" is therefore sometimes warranted. Care should be taken to avoid "straddling" large rocks as they may damage part of the vehicles drive train or other vital components. If the large rock cannot be driven around then the best and safest thing to do is steer a wheel directly over the obstacle. Getting up the obstacle is generally not too difficult unless traction is lost, but one must take great care as the tire comes off the rock in order to avoid damage to the vehicles rocker panel. (This is why it is important to have "rock rails" for serious four-wheeling adventures.)