Video Comparing First 4 Generations Of Jeep Grand Cherokee Shows Why Solid Axles Are So Good

The 2002 Jeep Liberty is considered by most diehard Jeepers the beginning of the end. Out went the boxy, rugged Jeep Cherokee XJ, and in its stead came a soft, round SUV with an uninspiring powertrain and — worst of all — independent suspension. This video comparison between the first four generations of Jeep Grand Cherokee shows why diehard Jeepers were so disappointed.

Before the Land Cruiser folks get upset, I’ll admit that, for lots of off-road scenarios, independent suspension is superior to a solid axle. In fact, I said the current most capable off-road vehicle in production is the Ford Bronco Raptor, which has IFS!

But, for low-speed off-roading, a solid axle is — in my opinion as a longtime off-roader and engineer — usually superior. At least, in passenger vehicles, that is.

It’s a combination of factors. First, a solid axle, with its basic tube design and serviceable/durable universal joints in the axle shafts, tends to be a more durable and repairable option for off-road trails. Second, a solid axle design is easier to lift than an independent suspension design since the only change in driveline angle is that of the driveshafts, which tend to be long and therefore not as steep as halfshafts (which take on a steeper angle when you lift an independent suspension). Third, there’s articulation.

And while I could make a list about how IFS is superior in some ways (less unsprung weight means going fast, especially on uneven sandy terrain, yields more traction and is about 100000x more comfortable), right now I just want to show you this random video I found of a little suspension/traction comparison between the first four Jeep Grand Cherokee generations: ZJ, WJ, WK, and WK2.

As a bit of an introduction, the ZJ was a huge deal back in its day. It took a formula pioneered (pun intended) by the Jeep Cherokee XJ — pairing a unibody with two solid axles — and built upon it. It kept the XJ’s track width, extended the wheelbase a bit, fixed the XJ’s cooling system inadequacies, and took the XJ’s Quadra-Link front suspension and adapted it to the rear, creating the Quadra Coil. The Quadra Coil went on to become the standard for off-road rear suspension designs, with everything from the Land Cruiser, Bronco, 4Runner, FJ Cruiser and so many others adopting the excellent suspension layout consisting of a track bar, two upper control arms, two lower control arms, coil springs and shocks (some separate, some coilovers).

In fact, the Jeep ZJ would go on to be the only Jeep ever to pair a relatively lightweight and stiff unibody design with a fully coil-sprung five-link suspension front and rear. (Some call it a four-link, ignoring the track bar/panhard rod). Here you can see the ZJ’s excellent suspension setup, courtesy of suspension seller Super Pro:

You’ll notice two lower control arms (or trailing arms), which are there to place the axle in the longitudinal direction (i.e. fore-aft), you’ll notice a track bar/panhard bar that places the axle in the lateral direction, and you’ll see two upper control arms/trailing arms to prevent axle wrap (i.e. the axle twisting) when braking or acceleration.

Here you can see that this is essentially the front suspension, but flipped around:

This sensational suspension design — which offers a ratio of comfort:suspension articulation never before seen in a dual solid axle vehicle — would never be seen again on a unibody Jeep, though the ZJ’s successor, the WJ, offered a strange variant of the design. Instead of having two upper control arms in the back, the WJ offered a single triangulating arm that attached to the top of the differential pumpkin via a ball joint:

This design works essentially the same way as the dual upper control-arm design, though the way the bushings/ball joints allow freedom of motion is a bit different than the way the ZJ’s upper control arm bushings flex to allow motion. But again, it’s similar.

In 2005, the WJ went away and was replaced by the WK, which reverted back to the ZJ’s dual control arm rear suspension, and then replaced the solid front axle with an independent suspension setup like this:

And then in 2011, the Jeep WK2 came with a fully independent suspension setup, appending that front suspension shown above with a fully independent rear suspension like this one:

In terms of off-road articulation, solid axles — at least on production vehicles — tend to outperform independent suspension setups. And I’m not just talking about overall wheel travel, I’m talking about the way a vehicle flows over the terrain: cross articulation.

Our suspension engineer-contributor Huibert Mees broke it down in his article “Our Suspension Engineer’s Take On The ‘Solid Axle vs Independent Suspension’ Off-Road Debate,” writing:

The ability to keep all tires on the ground means having a lot of something called “cross articulation,” This refers to the ability of the axles to twist in opposite directions. It’s measured with a ramp as shown by this Jeep here and is measured with something called the Ramp Travel Index (RTI):

[…]

The reason why the Jeeps are still better for RTI is likely because of differences in available wheel travel and the stiffness of the springs. It’s pretty easy to design a solid axle to have lots of wheel travel. Independent suspensions have limits in how much angle the halfshaft CV joints can tolerate and how much articulation you can get out of the ball joints. Both of these limit how much travel you can design into an independent suspension. Without knowing the exact values for travel and spring rates for both vehicles it is difficult to know for sure, but once the stabars are disconnected, the only thing limiting RTI would be available wheel travel and spring stiffness.

In case you’re curious, here’s what an RTI ramp looks like, and how much better a stock solid axle XJ does over a fully independent suspension-equipped KL Cherokee (the successor to the “beginning of the end” KJ Liberty I started this article out with:

Anyway, back to the reason why I wrote this article in the first place: Someone compared four generations of Jeep Grand Cherokee! That’s just cool.

And as with the old vs. new Cherokee comparison shown in the video directly above, the new vehicles have better traction control systems, while the old vehicles offer better articulation (and with aftermarket locking differentials would be far superior on the terrain in question).

The YouTube channel that shot this comparison, Jeepeando Con Peri, did a great job showing just how much more stable the first two generations of Grand Cherokee (the ones equipped with two solid axles) are than the third and fourth-gens. And even the gap between the rear solid axle-equipped third-gen WK and the fully independent suspension-equipped WK2 is significant.

Just look at how high the WK and WK2’s wheels get off the ground! That’s not only an issue with stability (and as a drive, this tippyness is disconcerting), but it’s also a traction issue. A tire not on the ground cannot help propel a vehicle forward.

The newer computerized traction control systems keep power to the wheels that are still on the ground, so even the less flexy vehicles are able to handle this undulating dirt course. The ZJ’s Viscous Coupling-based primitive four-wheel drive system holds it back a bit, though some momentum helps the vehicle get through all the obstacles without issue.

The best performer, as you can see in the video, is actually the WJ, because it combines a state-of-0f-the-art-as-of-1999 traction control system with two highly articulating axles, resulting in what looks like the easiest little off-road stroll that driver has ever seen.