Jeep Wrangler TJ Stealth Wheelbase Stretch KitPosted in How To: Suspension Brakes on June 1, 2010 Comment (0)
Some of the most important geometric elements of a four-wheel-drive vehicle are approach and departure angles, as well as ramp breakover angle-the angle that's measured by drawing a straight line from the trailing edge of the front tires or from the leading edge of the rear tires in order to a location on the frame that's midway between the two points. With high ground clearance and relatively large tires, a typical Jeep has a tall breakover angle and short overhangs, and is less prone to hanging up and dragging its bumpers and undercarriage over obstacles on the trail. However, that nimbleness on narrow, rocky trails comes at the price of a higher center of gravity which can affect performance on steep hillclimbs and descents, and which can also result in a tippy and wallowy-feeling ride on pavement. Also, a rig with a relatively tall breakover angle and a higher center of gravity can be more prone to driveline and steering angularity problems, particularly if larger-than-stock tires are installed.
On the other hand, a vehicle with a longer wheelbase, and hence a lower breakover angle, is often more able to straddle steep rocky hillclimbs and downhills than a shorter-wheelbase rig, and its lower center of gravity (assuming tire sizes are equal) results in a smoother ride on pavement and graded roads. Steering and driveshaft angularity problems are minimized, too, though new drivelines, U-joints, and extended-length steering and brake-line components would obviously need to be ordered if you stretch your wheelbase an inordinate amount. If your trail Jeep is also your daily driver, though, a longer wheelbase can be a modification worth looking into.
That is why we decided to investigate the growing trend associated with wheelbase extensions for Jeep TJs. Everyone knows that a longer wheelbase can improve a vehicle's ability to straddle ruts and climb steep hills, but given the price of such modifications, it is often difficult to quantify a return on the investment. We looked at three different wheelbase stretch kits available today and studied the pros and cons to see which kit presented the best value for the dollar spent. We picked the one kit we thought best demonstrated the benefits of such a conversion and installed it on a friend's daily driver, a '97 TJ. Our plan was simple: evaluate the kit and take notes on what it was actually like to live with for a typical year. Our results may surprise you.
The Lowdown on How It's Done
Each of the three TJ stretch kits we studied achieved the same basic goal of lengthening the wheelbase. However, one kit in particular outshined the others in terms of component quality, fit and finish, and completeness. Satisfied with our investigative work, we requested the Stealth Stretch manufactured by PureJeep of Bakersfield, California. PureJeep's system impressed us because of several details that were not addressed in the other kits.
The price of each kit was also taken into consideration, and the Stealth Stretch had a clear advantage over others we looked at. We liked the fact that the entire conversion comes from one company, and the kit includes everything needed to complete the conversion except for lengthening the rear driveline. Also, due to the nature of the kit, we figured to improve our Jeep's departure angle-without a lift or bigger tires-while maintaining front approach angle and gaining the benefits of a longer wheelbase in the process. To make the project happen, we enlisted the Jeep specialists of JC Fab in Sylmar, California, to ensure that each component was installed as intended.
The kit requires permanent modifications to the vehicle's body, so it goes without saying that mechanical experience is a key to the project's success. Additionally, the setup required revisions to the rear suspension, so it's good to have a basic understanding of link suspension arrangements. JC Fab's owner Jim Cox was more than qualified for the conversion, thanks to his extensive background in high-end Jeep buildups and custom fabrication.
This photo shows all of the rear suspension-related items included with the Stealth Stretch conversion. The PureJeep system uses suspension components from its sister company Full-Traction Suspension. Full-Traction has been building three-link Jeep suspension systems for years, so combining all of the proven parts into one complete system is a natural fit. The completely adjustable three-link setup shown employs a stout upper V-bar and lower adjustable control arms to locate the axle. This setup allows you to ditch the rear track bar, thus changing the way the rear axle and suspension cycle. Instead of the rear axle moving side-to-side in relation to the chassis throughout the range of motion, the new arrangement keeps the pumpkin centered under the vehicle as the suspension reacts to terrain inputs. Fully bolt-on, the kit also includes laser-cut coil-spring frame relocation brackets with retainers to prevent coil movement and noise under extreme articulation.
Living With a Stretched TJ
Nearly a year after we completed this conversion, the most obvious improvement is the drastically improved departure angle. By moving the rear end five inches to the rear, the setup improved our rear departure angle by at least six degrees. However, it came at an equivalent loss in ramp breakover angle. On the upside, on-road handling and ride quality vastly improved. The longer wheelbase helps to smoothen out the freeway expansion joints and harsh transitions between pavement and other surfaces. For what it's worth, our favorite thing about the conversion is the fact that in addition to lengthening the wheelbase, it solves three ancillary challenges faced by most TJ owners.
These include: fuel tank protection, rear quarter-panel and corner protection, and an annoying issue related to the factory rear suspension arrangement. To us, the most welcome and important of these added benefits is the latter. Without a rear track bar, the suspension cycles more freely in a straight up-and-down orientation instead of a side-to-side arc. This creates a more stable on-road feel while allowing additional inches of unrestricted articulation in the rough. Furthermore, the adjustability afforded by the new three-link enabled us to fine-tune the rear-axle pinion angle to better match the operating angle of the rear driveline.
Speaking of the rear driveline, a longer shaft enables an additional slip section and a less acute operating angle, which translates into prolonged U-joint and CV-joint life. We also love the newfound flexibility in rear shock length afforded by the kit; as a result, we plan to use this rig for a future shock test story. Around town, only the most detail-orientated Jeep enthusiasts notice the additional wheelbase length, but on the trail, the added inches become obvious, emphasizing the legendary capability of the TJ chassis.
The Jeep climbs better and soaks up bumps better, and as a result, we would rate this conversion a solid nine out of ten. We found only one fault in the fact that the included gas cap is not the locking type. Otherwise, the system is a good example of the old saying, "Longer is better."
|Adding up the Costs
(at time of print, no labor included)
|Stretch Kit||P/N PJ8256||$2299.95|
|Driveline lengthening (est.)||$210.00|
|Total cost of conversion||$2,509.95|
|Three-Link Stretch Bed Side Panels|
|Upgrade Kit||P/N FTS750801||$1,195.95|
|Fuel Tank||P/N PJ5125||$695.95|
|Stretch Bed Side Panels||P/N PJ4012||$339.95|