To answer this question we will start by discussing the need for a track bar at 2.5 inches of lift. The higher you go, the more the need increases. This is because front track bar connects to the frame mount on the driver’s side and the axle mount on the passenger side. The rear is the opposite. At ride height, both axles are centered (or very close to). As you go higher, the fixed length of the track bar becomes obvious. The axles are then "pulled" over to the frame mount side as the horizontal distance between the frame and axle mounts decreases due to the increasing angle of the bar (caused by the increasing vertical distance caused by your suspension lift). It is just a changing triangle where the track bar is the hypotenuse (constant). As the short (vertical) side increases and the long (horizontal distance between the mounts) side decreases, the angle of that hypotenuse has to increase. When you want to center those axles at ride height again, you'll need a longer track bar to "push" the axle back over away from the frame mount.
That being said, the axle will move about an inch with 2.5 inches of lift. Most 2.5 inch lift kits come with a bracket that will correct the geometry in the rear. Some Jeepers think the bracket provided in the kit creates a weak point in the suspension however many Jeepers run the bracket with no problems.
At 2.5 inches of lift not having an adjustable track bar won’t cause any problems. However, some Jeepers find it aesthetically displeasing and others are more meticulous when it comes to maintaining OEM driveline geometry. As I said at the start, the higher you go, the more the axles move and the more the need increase for an adjustable track bar.
Should I buy a Rubicon?
The first benefit the Rubicon has over other models are the 4.10 gears. This lower gear ratio (inside the deferential) allows for bigger tires with less need for regearing and also provides a better gear ratio for trail driving with stock Rubicon tires. Some Jeepers will argue that you need to regear, even with 4.10, gears once you get to 35 inch tires. It is recommended that you get your tires and THEN decide if you want to regear.
Another difference between the Rubicon and the other models is the 4:1 transfer case. For sand the 4:1 transfer case is not needed but it is no disadvantage either. Bogging in soft sand and then needing to downshift can contribute to getting stuck, the 4:1 transfer case will keep the revs up. Arguably this could also be accomplished by selecting and staying in a lower gear with the 2.72:1transfer case (that is the transfer case found on other Jeep models). The 4:1 transfer case probably provides the biggest benefit when climbing steep inclines and traversing obstacles, especially in a six speed. The torque is so high the vehicle is virtually impossible to stall.
Another benefit of the Rubicon is the front D44 front axle. This axle is the same axle found on the rear of the Rubicon and the rear of other Jeeps (other Jeeps have a Dana 30 in the front). The Dana 44 axle provides more strength when torque is applied to the wheels (i.e. hard acceleration in deep mud or snow) and when Jeeper decides to put on larger tires which, in turn, will amplify the amount of stress applied to the axle when torque is applied, especially when the lockers are applied.
The lockers are the most expensive and perhaps best feature of the Rubicon. I will explain what lockers do; If you were to take a regular four wheel drive vehicle (which has open differentials) and get it stuck with one side of the vehicle in deep snow and ice, and the other side on blacktop and try to accelerate, the wheels in the snow and ice would spin and the vehicle would remain stuck. When you turn on the lockers, (essentially eliminating the differential and locking both sides of the axle together) the torque will be forced to all four wheels providing torque to the wheels on the blacktop which would free the vehicle. So, a four wheel drive vehicle without lockers is really two wheel drive because the wheel with LESS traction on each axle will spin until the locker is applied.
Other Jeep models (including the Rubicon) have “Brake Lock Differential” (BLD) which is a kind of locker substitute. It works by applying the brake to the spinning wheel to force torque, through the differential, to the wheel with traction. This IS NOT the same as a locker. Over time the brakes will over heat. Additionally, BLD is reactionary. There has to be wheel spin for it to activate. By then you’re already behind the traction curve. I am going to end the BLD discussion there. If you’re reading this and want more discussion on BLD post a thread and we can discuss it.
The next feature that will be discussed is the electronic sway bar disconnect. Having a sway bar disconnect allows for more travel of the axle when the vehicle is in situations where the ground is uneven. This is called “articulation”. Sway bar disconnects can be added later but they will be manual disconnects which can be difficult to work with and are generally inconvenient . The convenience of electronic sway bar disconnects can be compared to in cab four wheel drive engagement. In the past one had to get out and lock the hubs to get four wheel drive, that is unthinkable in this era of 4X4. It can be said now that “in the past one had to get out to disconnect the sway bar”. It’s a great feature.
Another feature of the Rubicon is the larger tires. The larger tire gets your differential off the ground. While a larger lift gets your body higher off the ground, there is only one way to raise the axles and differentials, and that is a larger tire.
Finally, the Rubicon has rock rails that protect the lower body near the doors. They provide side and undercarriage protection in that region. They are one of the most important off road additions since it pretty easy to damage that part of the body if you come down on an obstacle or turn too tight near an obstacle.
Hopefully this write up has helped you decide if the Rubicon is right for you!
Just one comment on the relative importance of a few of the upgrades that come with the Rubicon. For manual transmission JKs that will have oversized tires added, you want lower gearing for both off road and on road use. Being able to gear down low gear is more of an issue with the manual transmission than it is with the auto transmission. But top gear in the manual transmission is not as tall as it is in the auto transmission, so being able to achieve a lower geared top gear is less of an issue with the manual transmission than it is with the auto transmission.
So what am I trying to say?
For manual transmission Rubicons the 4:1 transfer case gearing gives them a big advantage, off road, and the lower geared transfer case is an important upgrade.
For auto transmission Rubicons the Dana 44 front axle gives them a big advantage, on road, because of the available 5.38 gear set that can be installed in the Dana 44. The auto transmission JKs don't need the low gearing as much for off road use as they do for on road use, because the very tall top gear in the auto transmission needs to be compensated for. Lower axle gearing, on road, results in better performance and better gas mileage with auto transmission JKs. 5.38s get better gas mileage than 5.13s, which get better gas mileage than 4.88s, which get better than 4.10s, etc.
What additional skid plates does the Rubi have? I thought all JKs had the skid under the tank and transfer case/gearbox and thats all. Rubi has the rock rails vs steps on the others.
x2. Skids are the same, it's the rock rails that are added to the Rubi.
AFAIK, the only variable with skids is the transmission, where automatics get a skid that covers part of the transmission (that sits lower than standards). But that's true whether it's a Sport/X, Sahara, or Rubi.
I'll remove the part about the skid plates. MoparToYou, that is good info but it may be better discussed in a gearing FAQ. I am trying to keep as short as possible. Ill take a closer look when i am not on my phone.
I'll add something about the rockrails too. They are very important.
very nice write up. the only thing i could point out is that other models came with 4.10's. i have an 07 jku X that came with 4.10's. but other than that the write up is good to go. i would have liked to get the rubi but i couldnt pass up the deal i got on my jku. i figured with the money i saved i will change things and add things as i need them. so far i havent done anything hard enough to need lockers.
2006 Rubicon unlimited, silver. 5.5" long arm lift. 35" BFG KM2's on 15" black steelies. skidrow steering skid and radiator skid . LOD rear bumper with tire carrier. Flowmaster 44 exhaust. .CB with tuffy Overhead storage . Offroad lights in bumpers front and rear plus 2 more on the winch hoop.