The Great Three-Way Suspension Test
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Have you ever wondered about the real, practical differences between a stock IFS truck, one that is lifted using qualify aftermarket components, and one that has been given a straight-axle conversion? Yes, we know about the difference in price. Thats important. But equally important are these questions: How do they handle on the street? And how do they work on the trail? We here at Four Wheeler wanted to know, and so did the folks at Off Road Unlimited (ORU) in Burbank, California. To that end, ORU obtained a ¾-ton 01 Chevy Suburban. We drove it and subjected it to our usual course of vehicular torture. Then the guys at ORU installed an RCD 6-inch IFS lift. We drove the truck again. Finally, the ORU technicians installed one of their own 8-inch live-axle conversions, which adds 2 inches of lift via brackets and can be used with lift springs of your choice to gain 4 to 10 inches of lift. After the conversion, we flogged the truck for a final time.
The first issue to consider when looking at a liftonce you get past the cost of this modificationinvolves on-pavement ride and handling. Our test loop consisted of a 100-mile drive over all kinds of surface-street and freeway conditions. As expected, the Suburban exhibited the most stable feel on pavement, and the best ride quality, when it was in stock form. The RCD IFS lift felt slightly less stable on corners due to the higher center of gravity (CG) of the truck, but overall the ride was only a little harsher. This was due to the fact that the stock Autoride shocks no longer were in use and that the front torsion bars were cranked up a little tighter. Overall this lift was nice to drive on the street.
The real surprises came from the ORU live-axle conversion. With this system the on-road handling and ride were surprisingly good. While the CG of the truck was much higher than stock, the body roll in corners was minimal. The custom springs ORU had built by National Spring were amazingly soft and provided a nice ride on the pavement. In addition, the King shocks were perfectly tuned, and absorbed the small bumps on the highway almost as well as the stock Autoride suspension did. Dont get us wrong, the on-pavement ride and handling of the live-axle lift wasnt as nice as that provided by the stock suspension. But it was pleasant enough that we would be willing to drive the truck to work on a daily basis.
The off-pavement behaviors of these three suspensions, though, really is what this story is all about. For this, our test loop consisted of the trails and controlled obstacles at the Hungry Valley SVRA area near Gorman, California. These include a frame twister, a mini-Rubicon, and other challenges.
In stock form, the Suburban had trouble just getting its front bumper over a tall curb on the street. When off pavement, it seemed to make contact with almost every rock on the trail. Handling on washboard roads at speed was nice, but whoops would cause the suspension to bottom out. Installing the RCD IFS lift provided more clearance for rocks and improved the approach and departure angles. This allowed the Suburban to tackle trails that we previously never would have considered. While there was greater clearance under the truck, the suspensions articulation was only slightly improved. On washboard surfaces the truck still handled well, but it was a little more top-heavy, thanks to the lift. The ride was a little stiffer, but this helped to keep the truck from bottoming out on small whoops.
By contrast, the live-axle conversion really shined off-pavement. The lift and suspension changes provided even more approach and departure angle than the IFS lift did. We also found that there was a lot more clearance under the vehicle as well. Not only did the live-axle swap increase the distance between the rocks and the truck, it also vastly improved the suspension articulation compared to either IFS system. In our testing, the live-axle-equipped Suburban was able to climb all the way to the top of our test obstacle with ease. The stock truck couldnt even make it to the first step and the IFS lift truck only went about half the way up. In our high-speed trail tests, the Suburban, in its live-axle configuration, rode like a dream. It was less harsh at speed than either of the other two systems, and it handled whoops like a thoroughbred horse handles hurdles. On the durability side, the new front suspension and Dana 60 axle are much stronger than the stock IFS pieces they replace. In addition, there is much greater availability of lockers and limited slips for the Dana 60.
Our evaluations show that the stock Suburban is great for hauling kids and gear around town and even on graded Forest Service roads. For running moderate trails, an IFS lift is a better choice than a stock suspension, but expect to have some small trade-offs in on-pavement ride quality and expect durability of the stock differential and CV joints to become an issue, especially with tires larger than 35 inches tall. The live-axle conversion was truly at home off the pavement and were confident that it can handle tough trails and come back for more. As a bonus, the live-axle conversion was civilized enough to drive daily on the pavement. While this kit is quite costly, its worth every penny if you want to do some serious four-wheeling, and still drive your truck daily on the street.
Editors Note: Three different tire sizes were used during our testing, 30-inch, 35-inch, and 37-inch. Tire size and construction and wheel diameter play big roles in ride quality and trail traction.