Jeep Wrangler TJ Lift - Engineered To The Nth DegreePosted in How To: Suspension Brakes on March 1, 2006 Comment (0)
It's an engineered thing-and Jim Frens understands. Back in the November 2004 issue, we introduced you to a new company from Carson City, Nevada, that was making some cool skidplates and suspension bits for Jeep YJs and TJs. At that time, Nth Degree Mobility's products had to be used in conjunction with other brands of lift kits, since the company didn't offer a full suspension kit of its own. Today, that's all changed. Nth Degree's owner, and former Jeep chassis engineer, Frens has been hard at work designing a suspension for the TJ that picks up where the factory bean-counters left off. Since Frens worked for Chrysler during the TJ's development, he saw a lot of potential in the vehicle's chassis that was left out for cost or regulatory reasons. Now that he has his own company, Frens is able to offer a suspension system that is engineered to the level of the original factory stuff, but offers performance the factory engineers could only dream about.
One of Nth Degree's primary goals with all their products is to not create trailer queens. A Jeep equipped with an Nth Degree suspension must perform better on the road as well as off-pavement. It must drive to the trailhead safely and comfortably, and then be able to 'wheel with the best of 'em. After 'wheeling all weekend, it should be able to take its owner to work all week without weird handling compromises. Having ridden with Frens around his road test course, and driving several TJs equipped with his long-arm kits-both on long road trips and over the Rubicon Trail-we can say enthusiastically that he has surpassed his goal. The silver '05 Unlimited we photographed for this article rides on 35s with a 6-inch lift. It can hike a front tire 42 inches over an obstacle before any other tire leaves the ground, yet it drives down the road with better manners than a stocker. We crawled boulders with it like a rock buggy, and then drove it over a mountain pass like a sports car. No stock or lifted TJ we've experienced has ever performed like this.
There are numerous reasons the Nth Degree suspension performs like it does. Many of them are just little details-small changes in tuning and geometry that amount to big performance gains. These are details that only an engineer with a lot of knowledge about chassis dynamics could figure out. Check out our photos taken during the installation of the 6-inch long-arm kit on this brand-new Unlimited, and also the shots taken during its maiden 'wheeling trip over the Rubicon. Our goal here is not a "How To Install It" article or a "Before and After" test, but rather we'll try to highlight many of the unique features of the Nth Degree kit that sets it apart from the others.
The Nth Degree long-arm kit is a substantial collection of parts. It took two full days for the guys at Nth to install it while we took photos. All the parts are CAD/CAM designed, laser-cut and precession-welded in jigs, before being powdercoated in a dark gray. The 2-inch-OD, bent, rear lower control arms are made from 3/16-inch, 4130 chromoly tubing and are post heat-treated after the bends and all the welding are completed. This kit we installed is a 6-inch version, but a 4.5-inch version is also available. A lot of engineering has gone into the springs, resulting in rates and heights that vary depending upon application. The front springs feature a fixed rate, while the rears are progressive to allow for load carrying while minimizing changes in ride height-and most importantly, handling. While this article focuses on the company's long-arm kit, there is also a standard-arm-length kit that still features many of the same trick components such as the GyroJoints, Stinger, Tummy Tucker, custom springs, and more.
The subassembly of the four GyroJoints is one of the first steps. These joints are used to mount the control arms to the frame. They consist of a steel ball, similar to a trailer-hitch ball, encased within two special durometer urethane sockets. GyroJoints offer 360 degrees of flexible movement and also provide "give" to isolate road harshness from the chassis. The different-colored sockets represent different durometers-the measure of the material's "spring rate." The white half is a softer material than the black half. It is installed to the rear of the front axle socket to cushion rearward blows encountered by the axle when hitting a bump, rock, or pothole. Unlike a metal-on-metal Heim joint and other "flexy" joints, a cushioned joint delivers much less jolt and/or vibration into the vehicle's chassis so it stays tight and crack-free. Your butt will appreciate this isolation a lot too.
With the control-arm rails installed (seen attached to right-hand framerail in this shot), the Tummy Tucker skidplate/tranny mount is next installed. The Tummy Tucker (TT) is probably Nth Degree's most famous product to date and replaces the deep-scoop, low-hanging factory "shovel" with a smooth, almost flat, 1/4-inch steel plate. The TT gives up only 1 1/4 inches of ground clearance below the framerails and can support the entire weight of the vehicle. Like most of the parts in Nth Degree's kits, the TT is modular. If you already own a TT, a Stinger, Shock Shifters, the company's front track-bar relocation kit, or various other bits, all these parts can still be utilized with the new long-arm kit, greatly cutting down on the cost of upgrading to long arms. Also, this modular feature could allow you to build up your Jeep in stages; however, if you opt for that approach, it would be a good idea to consult with Nth Degree's staff to make sure you have the best possible combination of parts along the way.
With the new mounting holes drilled, you can mark where to cut off the excess lower part of the bracket. This modification offers a clearance advantage in the rocks, but the bigger gain is in the suspension geometry and the way the Jeep's handling is improved. These are details best understood by guys like Jim Frens.
Yikes! This is quite a creation! Instead of just raising the track-arm bracket with an extension, Nth Degree has gone to great engineering lengths with this all-important and much stressed suspension member. This new bracket mount is triangulated to the axle, providing the strength needed to deal with the leverage created by the new, higher attachment point for the track bar. Also, note that this attachment point has been moved forward (so it doesn't interfere with the gas tank) and is at a slight (corrected) angle for proper geometry, allowing it to work in sync with the modified ride height. Since we shot the photos of this install, Nth informed us that they have developed a cleaner, simpler, total-replacement weld-on tower as an option for this bracketry.
Next comes the Stinger. This is another Nth Degree "invention" that completely changes (read: improves) the handling of a TJ, eliminating the weird axle walk and wiggle felt in both stock and lifted TJs equipped with short upper control arms. The Stinger replaces these upper arms, changing the rear suspension from a five-link to a four-link. The Stinger functions as a torque arm and is similar to those used under late-model Camaros, allowing those cars to hook up better during hard acceleration. The Stinger transfers axlewrapping torque directly into the center of the vehicle and frame, instead of directing it diagonally, creating the frame lifting/twisting motion that angled upper control arms exhibit. Not seen in this photo is the Slider under the diff, which, while forming part of the Stinger's bracketry, also is a skidplate for the differential housing and the U-joint.
This shot demonstrates the change in the shock mounting points. We installed some old yellow shocks for this photo. The shock on the left is in the new Nth Degree location, while the one on the right is still in the stock location. Note the improvement in ground clearance as the new mount tucks the shock almost inside the wheel.
Now, we'll move to the front of the Jeep and check out some unique features up there. (This shot is backwards. Sorry, but picture this track-bar bracket from the rear of the axle looking forward, and everything makes sense.) At the top of the photo is the stock TJ track bar with its tie-rod end mount that attaches to the driver side of the frame. The bushing end attaches to the axle on the passenger side of the Jeep. Most lift kits simply extend the axle mount higher and call it good. Many lifted TJ owners know all about how these brackets come loose and the mounting holes wallow out. 'Nuff said. Nth Degree provides a massive, upper-mount drop-down bracket that braces itself across the frame and utilizes a new, forged track bar originally intended for a Jeep WJ Grand Cherokee (shown below the bracket).
This shot shows how the upper drop-down track-bar mount fits onto the frame. One hole must be drilled for the passenger-side mount. The driver side mounts via a special tapered pin that fits into the original tie-rod-style mount. Note the new dropped location of the driver-side mounting point, which is now a through-bolt design to accommodate the bushing style mount of the WJ track bar. The hole on the OE mount on the axle is enlarged slightly to fit a 12mm bolt (the stock TJs are 10mm).
The new front control arms feature a clearance-friendly bend like the rears, but are gusseted with a steel plate sporting a laser-cut Nth logo. This gusset ties into the upper control arm mounting points on the axle. Like other long-arm suspensions, the Nth kit does away with frame-mounted short upper control arms in favor of a both-arms-merge-into-one single-arm design. Unlike other kits, the Nth design features a bayonet-type bushing mount at the rear of the upper "arms" that allows for lots of "give" to tolerate the rotational bind created when a live axle is attached at four points and tries to articulate. The Nth design allows for movement and hence offers more articulation and longer bushing life. The "dog-leg" bend in the control arms not only offers increased ground clearance, but also allows full lock of the steering without any tire rub.
Monotube gas shocks with remote reservoirs from Rubicon Express were installed on the Unlimited. These shocks, or their non-remote cousins, are the recommended shocks that Nth offers to complement their suspensions. (Twin-tube shocks from Old Man Emu can also be specified for the 4.5-inch kit only.) Note also the included extra-long braided steel brake lines and coil-spring spacer. While using a coil spacer on top of a shorter coil spring may seem like a cheap move, it is actually more costly and there is a very important reason for doing it. Coil-spring design includes what's called a "slenderness ratio." This is the ratio of the spring's loaded height to its diameter. Make a spring with a ratio over 4:1 with a soft rate, and all it will want to do is buckle to the side when compressed. TJ springs are so small in diameter that a 4.5-inch-lift spring is at the 4:1 limit, so a 6-inch longer spring is out of the question unless you make the spring rate stiffer. Since a key part of Nth's suspension performance is the frequency-based tuning of the springs, the spring rate wasn't "negotiable" to the company. So a spacer is the solution. Spacers may not look as cool as super-long coils, but this setup works. As with the rear, the front bumpstops have been properly spaced to prevent shock bottoming and also keep the tires from mangling the fenders on those "Baja" whomps.
Last but not least are QuickSilvers. These are Nth Degree's front antisway bar disconnects. Jim insists that the stock antisway bars should be utilized on a TJ for optimal street performance. To that end, if you want great articulation, the 'bar must be disconnected for extreme 'wheeling. The QuickSilvers feature a cam-over design that requires no tools to operate and can be attached or detached without the vehicle being level. When detached, they fold up and lock themselves into special brackets mounted atop the spring perches-no bungee cords needed here. In the stored, disconnected position, both the links and the 'bar are out of the way of the tires at full lock when at full flex-no more rubbing!
Forty two inches. That's what we got when we raised the completed Unlimited up with a forklift with the front antisway bar disconnected and the rear attached ... and the tires at street pressure (28 psi). Forty two inches of obstacle crawling before another tire will lift off the ground. And yet this TJ drives down the highway better than any we've driven before, stock or modified. This kind of versatility was unheard of just a short time ago and shows just what can be done with the right engineering.
How's this for clearance? Rolling on 35s, the Unlimited measured 19 and 21 inches of ground clearance at every point under its chassis between its axles. Note how the control arms are tucked up almost inside the framerails all the way to the tires. It will be pretty hard to snag this Jeep on a rock via low-hanging suspension components.