Superlift 4" Rock Runner Suspension

By Cole Ford
Superlift Rockrunner
Superlift's sway bar disconnects are easy to use.

Opening A Can of Worms
Anytime you make a modification to your Jeep you open a can of worms. The biggest can that you will ever open is probably installing a suspension lift (unless you are trying to stuff a rocket motor in your Jeep). Opening the can is not always a bad thing, though. It will usually lead you to do other modifications that you will enjoy and probably needed, anyway. Every time you modify some part of your Jeep some other part may be affected, even if you do not recognize that anything has changed. The following are some of the things to think about when lifting a Jeep and the worms associated with them:

Center of Gravity
Ok, call me master of the obvious here, but any time you raise the height of the vehicle you change the center of gravity. This is the balance point of the vehicle if it were suspended in the air. It is also the point that all the dynamic forces act upon (acceleration, deceleration, turning, etc.). The higher this point is from the ground, the less stable a vehicle typically is. The solution to this is to run a wider tire with appropriate offset rim. While this will help to stabilize the new higher center of gravity, the driver should also be aware of these new dynamics. This, of course, goes for any suspension kit, not just he Superlift.

Superlift Rockrunner
Dunlop 33" Radial Mud Rovers on Ultra 50 rims.

Rubber Room
Since we were just speaking of tires and wheels, let us follow through with that thought. The whole purpose of a lift is to make room for bigger tires to increase overall ground clearance, approach and departure angles, etc. Since the "Cross Trainer" needs to be a great off and on-road rig, we made the decision to go with "little big" rubber.

The 33x12.50R15 Dunlop Mud Rovers will give us the clearance and grip to do 80% of the trails while still offering the on-road manners we need for the daily trip to the office. To get them to fit correctly, we needed the correct backspacing on the wheels. Remember, the lift will give you the vertical clearance for the larger tires, but you need to have the right wheel backspacing to make the larger tire fit while turning the wheels. We chose to put a beautiful set of Ultra Type 50 polished aluminum wheels on to accomplish this. Our other option would have been to use a wheel spacer on the factory wheels like the ones from JKS Manufacturing. You can look for more detailed information on all of these items in future articles.


Superlift Rockrunner
Tire size and weight changes your overall drive ratio. Keep this in mind and pick the right gears.

Gear Head
The right gears are worth their weight in gold! Gears and gear ratios seem to be one of the most misunderstood aspects among four wheelers. I am not going to get into massive detail on this one now, however. I will give you something to think about, though. We will use the Cross Trainer as our example.

Our Jeep came with a 4.0L motor, 5 speed transmission, 3.73 axle gears and 30 inch tires from the factory. By putting on larger tires, we changed a couple of very important things when it comes to power and gas mileage. This first thing is very obvious. Since the tires are bigger, they change the overall drive ratio of the Jeep. The larger wheel travels a further distance for every revolution. This causes the engine to run at a lower RPM.

You might think that this is good at first. But it can be very wrong. Lets say the engine is designed to produce its most efficient power and mileage at 2500 RPM at highway speed. With the larger tires in place it may only turn 2200RPM at the same speed. This causes the engine to "lug" and work harder, which means that it is now eating up more of that expensive gas. Not to mention that you're off-road crawl ratio is now worse than it was before.

Here is the second part that is not often considered in the off-road world. There is a distinct difference between the "Sprung" and "Un-sprung" mass of a vehicle. The sprung mass is simply everything held up by the suspension. While un-sprung mass is everything below. The vehicles' ability to move and control un-sprung mass is more difficult than it is to control sprung mass. (That is why the large part of the vehicle is above the springs.) The amount of effect depends on the particular vehicle.

A good general rule seems to be that each pound of un-sprung mass = 10 lbs of sprung mass. How does this affect our Jeep? Each one of my stock tires weighed 51 Lbs. Each one of the new tires weighs 68 Lbs. This means that my Jeep has to move, stop and turn with the effect of 680 more lbs. of weight on-board. If you check a gear ratio chart you can see what gears you need to change to in order to regain your power and gas mileage.

Superlift Rockrunner
Superlift's Rockrunner kit is very complete and includes a new steering stabilizer.

Brake Point
You can probably see some of the obvious concerns with the brakes now. The increase in un-sprung mass will make stopping distances greater. Upgrading to better brake pads, stainless steel brake lines, etc will help in this area. If your Jeep has an Anti-lock Braking System on it you will need to make sure you have the right speedometer gear in the transfer case for the ABS to work like it did from the factory. The computer that controls the ABS measures wheel speed (larger tires=slower rotation per distance traveled) and compares this to the speed it thinks the vehicle is going to determine when to use and not use the ABS.

Vibe Time
Lifting a Jeep can cause all kinds of different sensations to flow into the driver's seat. Vibrations from a drive line that is too steep are one of the most common. The Superlift system came with cam bolts and a transfer case lowering kit to help correct the driveline vibrations. While this works fine in most cases, it does cause a loss in ground clearance and a shorter shifter in the cab of the Jeep. The loss of ground clearance is our main concern since we lifted the Jeep to gain ground clearance. A slip yoke eliminator kit with a longer drive shaft would be a much better option. These kits leave the transfer case in the factory position and eliminate the vibrations. JB Conversion and Tom Woods are great sources for these. Look for more detailed information on both soon!

Superlift Rockrunner
The springs squash nicely when fully compressed.

Little Stuff!
There are a few little things to remember after you install the lift too.

· Adjust the headlights downward a touch
· Adjust the parking brake cable
· Adjust the mirrors
· Don't "Armor All" the passenger side step. (Trust me on this one, your buddy has a lot farther to fall now.)
· Remember to watch where you are driving and not at your reflection in store windows. It's just a lift! You're not that cool yet! Keep reading in months to come and it will get much cooler.



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