In my opinion, right out of the box, the JK Rubicon model is arguably the best all-around OEM Jeep ever offered to consumers. As you can see in every off-road catalog, its available enhancements cover every aspect of possible improvements. One of the players in this JK parts frenzy is Rancho Industries, which offers its new 4-inch JK lift kit, and of course it's proven RS9000 adjustable shocks. Equipping a JK with a 4-inch Rancho lift kit and RS9000 shocks can give you a foot of clearance, room for bigger tires, and an improved ride both on and off the road.
According to Jeep information, 35-inch tires will fit under the JK's fender flares and on its spare tire carrier, and will clear the rear bumper as well. This may well be true, but not with Jeep OEM wheels with their inward offset, so I didn't want to try larger tires without first raising the Jeep. Since Jeep lists the ground clearance for a Rubicon as eight inches (not including the two center pumpkins of the Dana 44 axles), the Rancho 4-inch kit will give you a full foot of clearance. Remember, when you drop air pressure for improved traction, you lose some of those original eight inches (you can lose as much as two inches if you run really soft tires). A 4-inch lift could be the difference between a holed and leaky gas tank—sometimes difficult to get home that way—or a few scratches in the tank's paint.
It's amazing to me that Rancho's suspension engineers know to the fraction of an inch just what the springs' tension, strength, and bar diameter must be to produce exactly four inches of lift to a JK. But that's exactly what my JK Rubicon was lifted at each corner (original measurements were: left front, 35 1/4 inches; right front, 35 inches; left rear, 35 1/2 inches; right rear, 35 1/2 inches. Final measurements before the addition of the 305/70R17 Goodyear MT/R tires with Kevlar: left front, 39 inches; right front, 39 inches; left rear 39 1/2 inches; right rear 39 1/2 inches). All measurements were taken at the center of each fender flare. The Goodyear tires added another full inch to the total ground clearance. OEM Rubicon tires are 32-inch diameter, while the Goodyear tires are 34.2 inches in diameter. With the switchover to 17-inch diameter rims and the 5x5-inch lug pattern in 2007, tire and wheel companies were forced to fill the void as quickly as possible.
When you're ordering your Rancho lift kit, don't forget the Rubicon end links kit (RS6753B) if you own a Rubicon, it's needed to extend the control arms of the sway bar or the onboard computer will be affected. This is because Rubicon's have an electronic disconnect for the sway bar to allow more wheel articulation (at 8 mph, the sway bar is automatically reconnected). Sahara and X models do not have the electronic disconnect feature, so you don't need the kit with those models. Speaking of the computer, once you've completed all the installation steps, you should have the JK's wheels and tires balanced, the steering wheel aligned, and have a dealer tech recalibrate the computer.
During the installation of the Rancho 4-inch lift kit with RS9000 adjustable shocks, I decided to add Rancho's optional wireless remote control for the RS9000 shocks. Although adding this kit is not difficult—the hardest part on a JK is trying to find a location to mount the air pump—it is technical. The kit includes the handheld wireless remote, 12V controller, 12V air pump, five air valves (for the shocks—one complete extra assembly in case you need it), way more than enough air line, and a handful of tie wraps. Rancho's instruction sheet is as complete as anyone would ever need, and I have just two additional suggestions. One, in addition to the O-ring and gasket that comes with each valve assembly you may need silicone—either spray or gel—as I did, to fill in the imperfections that might be found in the machined face of the shock. When it comes to wiring the controller, Rancho says to connect it directly to the battery's posts; I suggest instead to wire it through the ignition so that it comes hot only when the key is on. Why? Because the controller is constantly monitoring the air pressure in the lines and will pump it up if needed, including in the garage or where ever the Jeep is parked.
With the addition of the Rancho remote control kit, air pressure in the tires and shock adjustment (through air pressure on their adjusting valves) work together to produce exactly the type of ride you prefer. Off-road, lower the tires' pressure and adjust the shocks to a lower number. I adjust the shocks on each axle when I lower the tires' pressure; the pressure and shock valve number depend on the trail's rating (i.e., the higher the rating, the lower the pressure and shock setting).
When I get back to the highway, up go the pressure and shock settings. Each shock has nine different settings. On the JK I started with it set at No. 7 but that proved too harsh on the Arizona roadways, so I adjusted it down to No. 5, which is perfect for freeway or two-lane roads (on a 2005 TJ Unlimited I owned for a year, it needed No. 9 for proper shock absorbing). Off-road, for trails rated at three or above, I set the shocks at No. 1; for a one or two rating, I set the shocks at No. 3.
Wanting to drive the JK on more technical trails, I decided I needed more aggressive and taller tires than the original OEM tires, and then Goodyear introduced the new MT/R with Kevlar. Since my 1982 CJ-7 had been equipped with 12.50x15 original MT/R tires for over eight years without the spare ever touching the ground, I felt the new MT/R with Kevlar would be an even better choice for the Arizona desert (where I live) than the originals; able to shrug off cactus spines with ease, provide added traction over the varied types of terrain, and fill the fender wells better (plus, they simply look good!). The new Wrangler MT/R with Kevlar became available in March 2009 in 30 sizes, including a 42-inch-tall version aimed at the most hard-core rock hounds.
Another thing not to forget about a jacked-up JK; you've raised the center of gravity (COG), and the guys in D.C. love to tell us that SUVs, especially those with higher COGs, have a higher tendency—pun intended—to roll over. While the higher COG wouldn't affect an experienced driver, it might cause an inexperienced driver to over-compensate during a rapid turning maneuver, which could lead to a condition of upset.
Something else to remember: aftermarket wheels with a wider offset could be a big help in effectively lowering the JK's COG. When you're out on the trail with your new tires and suspension, just be careful until you're used to the Jeep's higher profile so that you can keep the shiny side up.