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| http://www.4x4wire.com/jeep/reviews/more97/ | Short Cuts | ||||
| by: David
Gray |
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| On a 20o RTI Ramp at Sierra Trek '97 |
Page 4 - Performance and Tradeoffs
The ride.
On page one we covered some of the advantages and disadvantages of the reverse shackle configuration. Specifically we now have a much smoother ride and less wandering down the road. Bumps no longer "upset" the suspension and it feels much more stable, especially at highway speeds. The one downside was the increased brake dive upon hard panic style braking which we found could be controlled with firmer shock absorbers (A change in the setting on our Rancho adjustable shocks) without sacrificing much of ride quality improvements that we have gained.
The buggy spring adds another dimension to the on-road handling characteristics, and to really get a handle on it we need to look at some of the basic functions that are performed by leaf springs (besides acting as a suspension).
In
a leaf spring vehicle the springs are the primary method of locating the axle.
In order to have a stable, controlled driving experience the axles should be
fixed in position for & aft and side to side (laterally) and the axle rotation
needs to be controlled (this is the oft cited issue when discussing "spring
wrap").
Lateral
positioning is of critical importance in the front axle because the steering
mechanism acts to push the axle side to side when we turn. In order to increase
this all important lateral stability a panhard rod (AKA a track bar), is used
to help locate the axle in relation to the steering mechanism. This is why the
panhard rod must be parallel with the drag link or as the suspension moves up
and down over a bump, even with the wheel straight, the axle's movement through
a different arc will cause the wheels to turn back and forth - a scary feeling
at 80 mph in an open top Jeep!
If the ends of the springs can easily move laterally, then the lateral stability of the whole axle is compromised. With the shackle mount firmly welded to the frame (like the stock front mount) the shackle really can not move much side to side even with stock rubber bushings (Polyurethane bushings are firmer and since they restrict the lateral motion even more they help the suspension and steering to feel more controlled). This changes when we add the buggy spring. The buggy spring can flex and twist and this twisting can allow the spring end of the shackle to move further side to side. This means that when you steer you may end up pushing the axle around instead of turning the wheels. This situation is not very stable and you will definitely feel like the the jeep is driving you and not the other way around.
The panhard rod can control this and this modification should not be run without a good panhard rod (with no slop) installed! The instructions mention this - do not ignore the warning!
The best laid plans of mice and men...
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| Some good ideas turn out to be a bad idea in practice. |
I made a few mistakes when first installing and running this suspension:
RTI Ramp
The RTI ramp showed that we had achieved
a big improvement in articulation and helped us to identify a few things that
were still limiting the amount of flex we could ultimately achieve. With 4"
Pro-Comp lift springs it was able to initially ramp about 970. It would be easily
capable of doing more than 1000 but there were some other limiting factors that
we will need to correct. These include:
Modifications:
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| Original Mount |
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| Mount with side plates added |
A few things can be done to enhance the stability of the buggy spring setup. One of the first thing that we did of course was to eliminate all of the funky rubber pads that we first mistakenly added. Then we made sure that the panhard rod was installed correctly and had no slop. This corrected the vast majority of the quirks that we experienced when we first hit the trail with our unique setup. Going further, we added some side plates to the buggy spring mounting plates to enhance the lateral stability of the buggy spring. Finally when on road we can use a square U-bolt to hold the spring rigidly against the frame so it cannot twist - making the system very solid. This U-bolt can be taken off when off-road so we can take full advantage of the buggy spring's added flex. With these modifications on ProjectYJ2K I am reasonably comfortable driving this Jeep even at fast highway speeds and down twisty mountain roads.
Conclusions:
M.O.R.E. supplies a shackle reversal kit both with and without the buggy leaf. The kit without the buggy leaf uses a fixed rear shackle hanger that is not subject to any of the flexing and twisting issues that we had with the buggy leaf mount. For most Jeep owners who are simply seeking improvements in handling and ride and just a tad more articulation the shackle reversal by itself achieves all of those goals admirably and it is probably the more sensible approach. The buggy leaf is really for the serious off-road enthusiast trying to squeeze every ounce of off-road performance out of his leaf sprung Jeep while not breaking the bank or selling any organs. For those people the buggy spring provides one method to dramatically increase available articulation, though concurrent modifications may have to be made to other components such as shocks and rakelines to fully realize the potential in this system. The buggy leaf also introduces new complexities to the handling characteristics of the Jeep and anybody considering this modification must be ready to face those issues.
| Sources: |
| Mountain Off-Road
Enterprises Dept ORN PO Box 843 Rifle, CO 81650 Phone +1 (970) 625 0500 |
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