The Jeep Cherokee KL Trailhawk is a proven off-road vehicle; however, its independent suspension has some limitations. If you want to go fast, independent almost always trumps solid, but when going slow over really rough ground with big tires, solid axles are king.
The truth is both types of suspensions can be built to excel in almost any off-road environment, but not all suspension/axle types are necessarily easy or inexpensive to build.
Sand cars and desert racers have embraced independent suspension for a long, long time. Many cars and trucks that go fast off-road have independent suspension front and rear. Most are fully custom so you won?t find inexpensive swappable parts in the junkyard, but the aftermarket has embraced several independent front suspension (IFS) designs found in trucks and SUVs and support them with long-travel or heavy-duty parts. Independent rear suspension (IRS) designs are also very tractable for high-speed off-road use, but few OEM production designs are up to the task of heavy off-road use. We're still waiting for the market to offer something for the Cherokee KL platform.
What is independent suspension?
Each wheel and tire per axle is attached directly to the frame using one, two, or more control arms. The axle?s differential housing, containing the axle gears, bearings, oil, and differential are also affixed directly to the frame. This design allows each tire to move independently from the chassis and the other tire on that axle.
Independent suspension systems generally offer lower overall weight and less unsprung weight. Unsprung weight is weight that moves with the tires/wheels rather than with the chassis of a vehicle. Moving weight requires energy and controlling weight is difficult as that weight increases. Therefore, suspensions that have to react quickly to surface changes do better with less unsprung weight. This is true both on- and off-road.
Independent suspensions also allow for more control over the suspension geometry as the suspension cycles. Changing arm length ratios can help keep the tires of a vehicle parallel with the ground as the suspension cycles and or help impart a steering input as the suspension droops or compresses. Therefore, you generally see independent suspensions favored in motorsports where the suspension and axles move up and down rapidly and control of the axle movement is critical. Shocks control compression and rebound, and the lighter the load, the more effect a shock has over the control. This is also a good reason to upgrade to a coil over shock IFS compared to the OEM strut design.
One drawback of independent suspension is that when it comes time to add suspension lift, many mounting points on the frame need to be lowered to maintain factory suspension geometry. That means you may need large brackets that hang down and the points for failure increase rapidly.
The Aussie lift (and the commercial version by Hazzard Sky) work within factory IFS limits to provide a modest 1.25-1.5" increase in front end clearance at a rock bottom price. The recent Dobinson lift doesn't provide more clearance; however, it does provide more wheel travel, which would translate into more articulation if the sway bar links were not limiting movement.
Independent suspensions are inherently more complex and, therefore, push the KISS rule to the side. That?s not to say that they are weaker. More that there is added potential for wear points and failure points. Most independent suspensions require at least two axle joints per side where the direction of power from the engine has to be changed, and that has to occur in multiple planes for steering axles. More pivot points allow for more points of wear and potential damage that can stop a rig in its tracks.
In attempts to keep things light weight, most axle housings in modern independent suspension systems use cast aluminum for their differential housings instead of cast iron. It is hard to definitively say that aluminum is not as strong when it comes to serving as a differential housing, but it can said that the anecdotal evidence exists. It could be that these housings are optimized for weight and lack the necessary metal to keep them together, but it seems to be an issue. Several IFS aluminum front differential housings from a number of manufacturers fail when the going gets tough. This is especially true when larger tires are added and/or traction improving devices are added, but the same failures have been seen in stock 4x4s.
Locking differentials, lower gearing, and larger-than-stock tires increase loads that can contribute to a catastrophic failure in the differential housing. Toyota switched back to an iron diff after a few years of using an aluminum housing, and the Hummer H3 used an iron version of a previously aluminum front differential housing.
Conclusion: pay attention to the materials used and the reputation of any drive train and suspension components you plan on using and abusing off-road.
Happy trails,
Snowhawk