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2007 Jeep Wrangler JK Buildup - Project Jeeponomics

Posted in How To on September 1, 2009 Comment (0)
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Jeep|o|nom|ics (jep-o-nm'iks)
the act of spending a good portion of one's capital on aftermarket products, and/or modifications for one's Jeep, thereby enhancing both the Jeep's job performance and the economic health of companies offering the products and/or modifications in question. Also accounts for the acronym J.E.E.P. Just Empty Every Pocket.

Stim|u-lus Pack-age (stim'yoo-ls pak'ij)
a gathering of quality products and/or modifications together for the purpose of stimulating the performance of the vehicle in question. A by-product of this packaging is stimulation of the bottom line of the companies offering involved products. It is hoped that no pork is installed during this packaging.

4 WHEEL DRIVE & SPORT UTILITY MAGAZINE has yet another Jeep JK project to help you decide how to build up your own JK. Jeeponomics is the author's latest buildup involving a bright yellow, 2007 two-door. Despite its bright, happy color, this poor little Jeep was shown no love during its first year of life. Cast off by its first owner after only six months of ownership, it was then tossed about between brokers, auction houses, dealerships and wholesale hustlers. After traveling only 8,000 miles, it landed in my hands for the paltry sum of less than half of what it sold for new a year earlier! This violated Jeep had never even had its T-case lever shifted! Why do I tell you all this? Because under the current economic conditions, there are some screaming deals to be had on slightly used JKs. Half-price deals allow you to own one of the best factory Jeeps yet and have coin left to build it into your dream machine.

A Suspension for all reasons from American Expedition Vehicles
The first modification I performed on Jeeponomics was to install a 3.5-inch Nth Degree suspension system from American Expedition Vehicles (AEV). AEV has become well known in the Jeep world as a premier player offering high end Jeep aftermarket products with design ties closely linked to Chrysler Corporation. When installed, AEV's products appear to have been designed and installed at the factory.

I picked up Jeeponomics in Portland and drove it 600 miles to its new home near Reno. This was the first time I'd driven a stock JK without suspension mods. I was impressed with its ride and handling at highway speeds on Interstate 5. For a short wheelbase Jeep, the little yellow JK handled a long highway road trip like no TJ, YJ, or CJ I've ever driven. I vowed (knowing that I wanted to lift this Jeep for larger tires and improved off-highway performance) that I wouldn't screw up its good highway manners by over doing its suspension. This vow led me to AEV's new Nth Degree JK suspensions.

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Nth & AEV
The man behind AEV suspensions is Jim Frens, a former Jeep engineer with Daimler/Chrysler and the father of Nth Degree Mobility suspensions. Nth Degree made quite a name for itself in a short period of time offering (among several products) a unique long arm suspension for the Jeep TJ. The Nth suspensions are known for providing serious off-road wheel travel, yet manners on the highway that out perform a stock setup. The entire Nth Degree TJ suspension line is now owned and offered by AEV. With the ownership of Nth came Frens, and now his talents have been channeled toward designing a suspension upgrade for the JK that enhances both it's on-and-off-highway performance, perfect for a true, all around "American Expedition Vehicle."

JKs ain't TJs
At first glance, the Premium 3.5-inch suspension featured in this article doesn't appear to contain a lot of parts - and that's the beauty of it. Where are the new control arms? Well, the blunt answer to that is, stop thinking TJ! With the TJ, it became a "lift-kit standard" to replace control arms, either with beefier stock length or longer arms because TJ arms are short and weak. For a TJ to run 35 inch tires it require a 4-inch lift. For it to retain any suspension manners at that height, a long arm kit is necessary. Despite the JK's suspension looking similar to a TJ's, the JK chassis is entirely different with subtle geometry changes that a guy like Frens can recognize and work with. Bottom line is a JK can handle 3 to 4 1/2 inches of lift without the need of longer arms, different pickup points and all the associated hardware and complexity that goes with a suspension of this type. Stock JK arms are as beefy as any aftermarket replacement arm and feature quality, factory-durability-tested bushings that will last a long time. Why throw them in the dumpster just because "that's what has always been done?" AEV decided that for your money, they would offer features like exclusive frequency-tuned springs, Bilstein shocks, and engineered brackets that address real geometry issues (see below) instead of selling you old school thinking and forcing you to throw away perfectly good parts.

A Swiss-Army Knife Jeep
With the JK, American Expedition Vehicles had a pretty good platform to start with when designing an ultimate exploration-type vehicle. AEV's focus is on a Jeep of this nature, not an all-out, one-dimensional rock crawler. AEV's vision is a rig that can carry its owner thousands of high-speed highway miles with stability and comfort while hauling perhaps a month's load of supplies, tools, fuel, etc. This same Jeep would then be capable of turning off highway and traversing the roughest of terrain, offering articulation, ground clearance, traction, and stability, while still carrying the same load and offering the same comfort it did back on the highway.

A good exploration/expedition rig needs relatively big tires and a healthy dose of ground clearance. Unfortunately, these two features a stock JK sorely lacks. AEV's Nth Degree suspension certainly addresses lift and provides for larger tires, but there is much more engineering going on that can't be seen, but can certainly be felt when driving. The company offers two heights: 3.5 inches for 35 inch tires, and 4.5 for 37 inchers. The suspensions are available as "Standard" or "Premium," with the Premium kits mainly including enhanced steering components and a magic black box for adjusting your computer (more on this later). Standard kits are only available with the 3.5 inch lifts, all 4.5 kits are Premium. Both kits provide progressive-rate, frequency-tuned lift springs and vehicle/load-specific-valved Bilstein shocks built to Jim Fren's specifications and AEV's exacting standards. Designing progressive springs and matched shocks that provide lift and a good ride are only part of the equation though. Frens felt from the beginning that the JK's on-road handling behavior could be improved by addressing its rear roll center.

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A Few Geometry Issues
To understand roll center a quick look at suspension geometry is necessary. The largest contributor to good vehicle handling with a live axle is how its rear suspension tracks in response to body roll when the vehicle is committed to a corner. The lean of the body during cornering causes the suspension to compress on one side and lift on the other, changing the angles of the suspension's control arms and allowing the axle to literally steer the rear of the rig. On a short wheel travel sports car with a low center of gravity (c.g.) this effect can be used by chassis engineers to enhance the car's handling by inducing roll-understeer. On a high c.g. 4X4 with lots of wheel travel, (i.e. a Jeep with a 4-inch lift and soft spring rates) the potential for lots of rear axle steer is present, leading to squirrelly, roll-oversteer handling. This rear steer can be reduced with properly placed, longer control arms if packaging allows. The key words here are "properly placed" and "packaging," neither of which works on a JK that needs axle ground clearance and has a gas tank in the way. On most lifted 4x4s, controlling this rear steer problem is best addressed by using anti-roll bars and proper roll center geometry to "dial in" the tall vehicle's handling. What about springs and shocks? Spring rates predominately come into play for optimal straight line ride and shocks are mainly "motion attenuators." They are there to "reset" the suspension for the next bump and help control transient bump response between the front and rear axles. One could "dial out" body roll with super-stiff springs, but all you'll get is a crappy ride and lousy articulation for 'wheeling. So back to anti-roll bars and roll center. Any Jeep owner who has driven their rig with it's anti-roll bar(s) disconnected has experienced crazy body roll and can understand how these "stabilizer" bars can help limit body movement and hence, limit rear axle steer. But what is roll center all about and what is wrong with it on the JK?

RC, C.G., and RMC.
What the...?

The roll center (RC) of a JK is the point along its suspension's track bar where it intersects with the vehicle's imaginary vertical centerline. Somewhere above the RC, along that same centerline, is the vehicle's center of gravity (c.g.) point. Now, to really confuse you, the distance between those two points is the vehicle's Roll Moment Couple (RMC). RMC determines how much leverage is available to cause the vehicle to lean in a turn. The bigger the RMC the more leverage and body roll. For a given spring rate, as RMC is reduced, body roll is reduced, and as body roll is reduced, so is the effect of rear axle steer (squirrelly handling) brought on by the poor geometry angles of the control arms (remember, one is up and one is down when cornering, causing the axle to pivot and steer the rear-end).

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Where Are We Going?
So where does all this mathematical confusion lead us in regards to JKs, Jim Frens, and American Expeditions Vehicle's suspension featured in this article? As I mentioned above, Frens feels that Jeep got the stock JK's roll center wrong from the factory. Add a 3-inch suspension lift (so c.g. goes up 3 inches) and no rear track bar relocation, and the vehicle's RC goes up by half, or 1.5 inches. This increases the RMC by 1.5 inches, which increases the body roll, which increases the axle steer and on-road handling really suffers. Correcting the track bar angle with a 3-inch taller relocation bracket on the axle will place the track bar (and the RMC) back to stock geometry and the lifted JK will handle similar to stock. However, Frens feels that the stock RMC is too large for the rest of the chassis design. In designing the AEV/Nth Degree relocation bracket, Frens made it a full 6 inches taller, three inches more than where it would be relocated to if maintaining the stock position on a 3-inch lift. This reduced the RMC to what Frens feels is the optimal amount for the JK chassis. As a consequence, handling of the lifted AEV-equipped JK is equal to, if not slightly better than stock! This was proven by Frens at Chrysler's Chelsea proving grounds where he and other Chrysler test drivers beat a bone stock four-door JK over the company's slalom course with an AEV-equipped 3.5-inch-lifted four-door on 35s!

A Happy Jeeponomics
Keeping true to my vow to not screw up my stock handling, the installed 3.5-inch Nth Degree "Premium" suspension kit from AEV has actually improved Jeeponomics' on-road handling while giving me the off-road ground clearance and fender clearance I wanted for Interco's new 35X12.50R17 SS-M16 tires seen in the photos (check out the sidebar for info on these newest Intercos and the AEV DOT-legal beadlock wheels I wrapped them around.). Overall, the ride is slightly firmer than stock but this helps control the added un-sprung weight of the 35s. Two niggling issues I had with the stock suspension were: 1) what I call "the jiggles" where you find all of your body just sort of jiggling when driving over mildly rough roads. The jiggles are worse in a TJ, (as is "head toss") but a JK has this phenomenon too, though to a lesser extent. With the AEV suspension the jiggles are gone! 2) When running semi-fast over whooped-out sections of trail, the front suspension would soak up the shock surprisingly well, only to have the rear really bottom and kick up the rear-end of the car - a harsh and somewhat squirrelly situation. It was a good example of poor "bump disturbance management" (as Frens would say) and one that has been fully addressed with his frequency-tuned springs and vehicle specific-valved Bilsteins. Jeeponomics is now "tail-happy" with no more rear-end kicks and can run pretty quickly over pretty rough terrain for such a short wheelbase vehicle.

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The "Standard" AEV suspension comes with springs, shocks, a new rear track bar, and track bar relocation brackets for the front and rear. I opted for the "Premium" suspension, which adds "steering correction" parts in the form of a new, high-steer drag link and a beefier steering stabilizer. Also included is perhaps the most innovative offering found in a "lift kit" yet; AEV's new ProCal module, which calibrates the JK's computer after adding taller tires and/or different gears. This magic black box is the size of a cell phone and plugs into the JK's OBD II port. By simply setting a series of dip switches on the ProCal, the rig's computer can be adjusted for tire and gear changes. Several other computer functions that may need attention after installing a lift can be addressed with the ProCal as well. And I can't forget the bright orange OE jack "lift kit" which rounds out the Premium package. Who else but AEV would think of that one - or go to the trouble to make it?

Before and After
Check out the photos for some before and after trail tests and highlights from the suspension install. In a future Project Jeeponomics article we'll look at some body armor...and that snorkel! Down the road will be some trick new axle options. Stay tuned for more ways to stimulate your JK and your wallet!

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AEV's Pintler Beadlock Wheels and Interco's new SS-M16
AEV wheels just seemed like a natural choice for a Jeep running an AEV suspension. Better yet, I like the don't-get-a-flat-at-low-air-pressure assurance beadlocks provide, and AEV's beadlock wheels have passed the current DOT-compliancy tests making me feel assured that they are safe on the street. Does DOT-compliancy mean they are street legal? Not necessarily. All state laws differ in regards to multi-piece wheels. If you are considering running beadlocks on the street, take a good look at AEV's website regarding beadlock info. It's very informative and will set you straight on the dos and don'ts of running beadlocks. That said, I'm running 'em and I'm happy. I take the responsibility of doing the maintenance required to enjoy the benefits of no flats at low pressures due to bead failure.

AEV's beadlock wheels are cast as a beadlock and are a one-piece design, not a modified normal wheel with a beadlock adapter welded on. To me this makes them truer, safer and less prone to leaks. The AEV Pintler-style wheel is available with or without a beadlock and is offered in silver or argent powdercoat. They are only made for Jeeps and feature optimized offsets for Jeep steering geometry. Other nice features are recessed valve stems and hubcentric centers for smoother balance. The wheels are also compatible with 2008 and up JKs with tire-pressure monitors (TPM).

I'm not sure where the name came from, and the bullets molded into the sidewalls are a bit over the top, but I like Interco tires. I have owned and run just about all of their offerings over the years, both recreationally and in competition. They are tough and dependable. They don't let me down. Project Jeeponomics seemed like a good rig to try Interco's newest offering, the SS-M16 which the company claims is a tire for all seasons, with features taken from both their all-terrain and mud-terrain designs. They claim to be a highway friendly tire and yet very aggressive off road. So far I've found those claims to be true.

I say so far because, as of the deadline to write this, I don't feel I've tested 'em under enough conditions. I've had them in a little snow and a little mud, dirt roads, and maybe a hundred highway miles. M16s have been called "street friendly Boggers" and during my limited time with them that appears to be true. They are tough as nails (bullets?). Their forward traction is awesome while their side holding abilities may be slightly ah, slippery. On road they are amazingly quiet for an aggressive tire and they are very round. I mounted them onto the AEV beadlocks and have been running them without any balancing. They are very smooth on the relatively-light Jeep, no shaking, wobbling, or morning flat spots. Their load range E, 10-ply construction (three-ply sidewalls) may be a bit too stiff for a Jeep. I've been running them at 20 psi and they could go lower. The 35x12.50R17LT size that I'm running is brand new (these were five of the first 16 made) and I didn't realize they would have such a high load rating. One tire will support 3,640 pounds at 65 psi, or almost the weight of the entire Jeep! I will play with pressures and do much more traction testing to bring you further SS-M16 reports in an upcoming Jeeponomics installment.

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Sources

Interco
337-334-3814
www.intercotire.com
AEV/Nth Degree Suspension
www.aev-conversions.com

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