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by Jim Allen
Tires, wheels and suspension will likely be your biggest investments in a Jeep buildup and you want that money to pay interest in the performance department. The starting point for decisions on the suspension is tire size. Everything else revolves around it. Tire size will dictate the cost and complexity of the job, the street driveability characteristics and the level of trail performance.
Once you’ve made the tire choice, you can start shopping for a suspension to match. Lift kit manufacturers will offer a “recipe” that matches a lift kit with a particular tire size. Sounds easy… and most of the time it is… but not always, because every Jeep is a little different.
The lift numbers and tire fit recommendations you see advertised are averages. The manufacturer
builds a kit around what they think is an “average” Jeep. You may get more or less
lift than the kit manufacturer lists because vehicle weight varies. A heavier vehicle will compress
the springs more than a lighter one and end up with less lift, or vice versa. It all has to
do with spring rate.
Spring rates are measured in pounds per inch of travel. A 400 lb/in. spring takes 400
pound to compress one inch, 800 to compress two, and so on. The kit maker plays the law of
averages so if your Jeep is lighter than average, you end up with a little
more lift and perhaps a stiffer ride. If you are heavier, then your
ride will be smoother and your lift less.
You need to be aware of this particularly if your Jeep has (orwill
later have) an engine swap, a heavywinch up front or lots of accessories.
If it does, you may not have the clearance for the tires you
have selected. In some cases, youmay find a selection of spring rates
available from a kit maker to suit your heavy Jeep better. If not, you
have several choices, from adding small corrective measures (read
on) to adjusting your tires size choice smaller to suit the available
space. One way to be sure is to weigh your Jeep on a commercial
scale and get front and rearweights.With that info, the lift kitmanufacturer
can predict how their kit will react to those weights and
help you make a better selection.
The best way to lift a leaf spring Jeep is via new springs. Lifted springs have more arch
and are slightly longer. Up to about 4-inches of lift, you can count on a good ride and good
travel but above that point, the amount of arch tends to interfere with ride quality and limit
uptravel more severely.
There are other lift methods you have heard about, including add-a-leafs and shackle lifts.
Add-a-leafs usually add an inch or two of lift at the cost of some ride quality, assuming the vehicle
weight remains the same. They are best used if an increase in spring rate is needed for
a heavy Jeep or to bolster sagging springs.
Longer shackles are great for correcting pinion angles but not so good as a lift device. The
longer shacklewill tend to tilt the nose of the diff pinion up on both the axles. That’s assuming the
front shackles are in the stock location
at the front of the springs. On Jeeps
with reversed shackles, a longer shackle
will tilt the nose of the diff down. Remember
that whatever lift a longer
shackle offers, is half of the increased
length fromstock. A shackle that is two
inches longer than stock will only offer
an inch of lift. If the pinion ends up in a
useful position, the extra lift from a
longer shackle can be used for ride
height correction as long as the angle
on the shackle remains tilted back from
vertical. Inmost cases, pinion angles are
corrected with the use of tapered
wedges that are sandwiched between
the axle and the spring. They often
are included in a lift kit but also come
separately in various angles.
Track bars on the ’87-96Wrangler
YJ offer a special complication. Lifting
a YJ with a stock bar tries to pull the
axle towards the driver’s side because
the eye-to-eyemounted distance is decreasedwith
angularity. There are several
cures, the usual is either relocation
brackets to drop one end or longer bars, either of which is included in a lift kit. There are also
adjustable track bars. Track bars definitely improve road handling and should be kept in place,
but they also restrict off highway articulation. Quick release track bars are offered to give you
the best of both worlds.
Coil lifts come in two basic forms, spacer lifts and spring lifts. Spacer lifts are inexpensive,
easy to install and effective up to about two inches of lift. After that, the uncorrected
changes in suspension geometry make them iffy in the driveability department.
Brick-simple, they consist of a spacer mounted between the coil spring and the upper
spring mount. It can be polyurethane, metal or even an adjustable spacer. A spacer lift is a
great choice for people who need the clearance for a mild bump in tire size from stock.
Spacers can also be used to level or correct ride height in combination with another type
of lift. A spacer lift comes with either shock extensions or longer shocks.
Spring lifts come in many varieties. They start with a simple spring swap alone, which
is just a longer spring that comes with either longer shocks or shock extensions.Without
correction, the spring lift has essentially the same limitations as a spacer lift, namely
about two inches of lift.
Two more spring lift categories are the short arm and long arm. The short arm type
uses control arms of a similar length to the original. These are corrected lifts, meaning the
geometry has been corrected according to the amount of lift. That take several forms,
most commonly longer lower arms and adjustable upper arms. It may also use drop brackets.
Speaking of upper arms, kits come with or without. A basic lift doesn’t necessarily
need new uppers for correction purposes, but the aftermarket arms are much stronger
than the OE. The OE upper arms sometimes fail in rough service when subjected to the
extra angularity of a lift.
Short arm lifts should be
kept to about three inches, four
at the outside, for the best driveability.
The more the lift, the
sharper the angle on the control
arms and the more adverse
street symptoms will be noticed.
These include a harsher
ride, more rapid control arm
bushing wear, a jacking effect
on acceleration, roll steer in
turns and so on.
There are exception to
the 3-inch rule, such as dropbracket
kits that move the chassis
end of the arms lower to
reduce angularity. These are
very viable alternatives that
offer very good trail performance
and good street manners.
Long arm kits are the top
dogs in the world of coilers. As
the name implies, they use
longer control arms, or radius
arms. This reduces the angularity
of the arms, which reduces or eliminates the negative driveability effects and increases
travel, even over a short arm dropped kit. They often combine other beneficial
modifications, such as a triangulated upper axle link in the rear.
The death wobble can occur with any 4x4 mounting big tires. It’s a steering oscillation
that comes at speed on the highway. It isn’t quite as dangerous as the name implies…but
will make you think it is! The primary cause is usually improperly balanced big tires. It can
also be caused, or amplified, by loose steering components. Beyond correcting worn steering
and suspension components, a good balance job will go a long way toward correcting
the death wobble. A key element in balancing is to use make sure the weights are placed on
both sides of the rim, not just the inside. Not as pretty…but a much better balance job with
big tires. The final element for death wobble avoidance is a beefy steering damper.
New shocks often come with lift kits. Shocks are not a “one-size-fits-all.” The first requirement
is that extended and collapsed shock length should match suspension travel.
Also, leaf and coil sprung Jeeps have somewhat different requirements for valveing, so a
good match is type specific. Piston size is an important consideration. Big tires increase unsprung
weight and you need a bigger shock to handle it.Within reason, you can’t go “too big”
on piston size if the valveing is correct for your general vehicle type.
Differences in shock requirements also come with the type of Jeeping you do. Jeepers
in the easy-wheeling category can get by quite well with “regular old” hydraulic shocks.
Most rock crawlers can too, but both categories can benefit from low-pressure gas charged
shocks. Fastmovers need high pressure gas charged shocks to dealwith oil foaming and heat.
Heat is the primary effect of lots of
fast suspension movement. Fast
movers often installmultiple shocks to
share the load. Dual shocks should be
valved softer for use in pairs or you
may end up with a rougher ride that
you like. Premiumor high performance
hocks are so good these days that only
a few people really need a dual shock
Liftswill increase driveshaft angles
and to avoid vibration and shortened ujoint
life, these need to be addressed.
Many lift kits include some means to
deal with this but you are well advised
to go beyond. Even a mild two inch kit
on a ShortWheel Base (SWB)Wrangler
will increase the driveshaft angle to almost
28 degrees from the stock 15 degrees.
With about 30 degrees as the
maximumangularityonavery short shaft,
something has to be done.
The first option is a transfer case lowering
kit,which reduces the driveshaft angles by lowering the transfercase/skidplate assembly. This
is accomplishedwith spacers, is simple to install and usually included inmost lifts. In leaf spring
applications a spring degreewedgemay also be needed.
With higher lifts, a better solution is a fixed yoke, slip-yoke eliminator kit for the transfer case a CV type two-piece rear driveshaft. This shortens the transfer case length by four inches or more, and that extra length in the rear driveshaft significantly reduces rear driveshaft angles and vibrations. These modifications also make the transfer case much stronger as well, and are suggested for serious off-road use. The more expensive kits have stronger rear output shafts and these are necessary if you have a 4:1 transfer case or a big engine.
While they do restrict suspension articulation in the dirt, operational sway bars are
important to highway safety, handling and driveability, so don’t chuck ‘em. That’s easier to do now that you can get sway bar disconnects for virtually any Jeep. Hooked up on
the street for good handling and unhooked on the trail for maximum articulation. Many
kits include them. If not, they are a worthwhile supplementary purchase.
There are several types of steering systems used on Jeeps, all susceptible to bump
steer when lifted. Bump steer is when suspension movement introduces unwanted steering
input and causes wandering or darting. It’s all about the angle on the drag link, which
connects the steering box to the tie rod. Ideally you want that link to be as close as possible
to parallel with the axle.When it’s not, the up and down movement of the axle
changes the end to end distance and in effect steers the vehicle.
The cure is a dropped
Pitman arm, which reduces
the angle of the drag link. On
YJs with track rods, the ideal
is to have the drag link at
the same angle as the track
rod, especially in those first few
inches of axle travel. The same
goes for the coil sprung TJ.
Big tires and ‘wheeling
puts a lot more stress on steering
components than the OE
engineers planned for. Two
common problems then become
the steering box mounting
and the drag link and tie
rod. Every ‘wheeling Jeep with
oversized tires should have a
steering box brace. They make
it much less likely that the box
will tear away from the chassis.
TJ steering boxes are vulnerable
to rockcrawling trail
damage, so a skid plate is in
order. Heavy duty tie rods and
drag links resist the greatly increased
bending forces applied by big tires These HD rods often come with high angle rod
ends that can tolerate the extra angularity imparted by lifts. At about 33 inches of tire diameter,
a steering linkage upgrade moves more into the “necessary” category.
Polyurethane bushings are the best choice for most rigs, most times. Especially in trail
situations, they will outlast OE rubber bushings by massive amounts. In leaf springs, they
allow for a little more suspension movement because the center sleeves move freely in
the bushing, unlike bonded rubber bushings. Many types are available in greaseable form,
which helps them last even longer and avoid the creaky noises Poly is famous for. Ply is
suitable for 99 percent of everything on Jeep suspensions. The exception are the coilers.
If used on the chassis end of the suspension link, they can transmit a lot of noise and vibration
that some find objectionable.
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