choices and options for building a 4
link suspension include a broad selection of control arm
joints, tubing and tubing adapters, brackets for the frame
and axle, coilover shocks or traditional coil springs and shocks,
bump stops and limit straps, and an assortment of mounting
tabs and housing bridges. Whether you're building a custom
system or improving an off-the-shelf system, you'll be able
to build a high performance suspension for your vehicle with
parts and components available from Foothill.
Approaching your system design involves many parameters--the basic
system (four link, four link with track bar, three link), suspension
travel requirements, vehicle height and weight, wheelbase, traction
considerations (squat/antisquat)--all of which factor into the components
you will need and how they will be assembled and installed. Foothill's
broad selection of components and parts will result in the exact
suspension you seek to build.
Actual design of suspension systems can be involved--entire books
have been published on the topic. However, there are a few critical
parameters to factor into your design that will result in a system
that performs well. Look for a tutorial from Foothill at a future
Control Arm Joints
Selecting the appropriate control
arm joint is critical to building a correct suspension. The joint
must flex and rotate on the desired axes and in the desired planes.
Certain joints can also be used to limit motion in undesired directions,
but they can't be stressed beyond the design limits of the joint
without damage to it. Ride quality, noise, and transmission of vibration
also factor into joint selection. Because there is a broad spectrum
of needs, Foothill Offroad has developed a wide selection of joints
to choose from.
| ||Rubber or Poly Joints
These types of joints are commonly found on factory systems
and many aftermarket suspensions. They provide a quiet ride
and excellent handling characteristics but are prone to quick
wear or failure when asked to flex at high angles. They are
a good choice for a joint where motion control on a single
axis is desired, such as a control arm that pivots around
the bolt only and doesn't twist side to side.
| ||Flex Ball Joints
Flex Ball Joints, commonly known as "Johnny Joints",
have a ball assembly that rides in poly races inside a steel
collar. They are a rebuildable and serviceable joint that
works quite well in many systems. Side loading can be an
issue with joints that use snap rings to secure the ball
and races--they can be forced out under extreme pressure.
For this reason, Foothill's joints use only one snap ring
and when installed correctly (opposing one another on each
arm) they will help one another with side load forces.
Flex ball joints typically can rotate about 20 degrees, making
them quite suitable for most suspension systems. They are
available in two sizes and either as weld on or thread in
Heim joints are popular and found in many applications--control
arms, track bars, steering, end links, and antiwrap controls
to name a few. They are available in a wide range of designs--steel
on steel, Teflon lined, hardened housings, and left or right
Heim joints are a ball and socket design that offers rotation
approaching 30 degrees. For greater rotation, high misalignment
spacers can extend that rotation, at the expense of mounting
bolt diameter. As a relatively hard joint, they quite easily
transmit noise and vibration, making them somewhat annoying
on rough surfaces at high speeds.
Control Arm Construction
Control arm tubing choices fall into two camps--heavy duty, thick
wall tubing that can take the abuse of punishing rockcrawling use,
or lightweight thinner wall tubing where weight is a consideration.
Foothill can supply either style of tubing for a variety of applications.
Weld-in tubing adapters facilitate the construction of control arms,
or thick wall tubing may be directly threaded for accepting a joint.
For lower control arms in "long arm" systems, 2" diameter,
.250 wall DOM tubing is a common choice. It is difficult to bend,
albeit a bit on the heavy side. Arms can be built with any of the
larger joints described above and the appropriate tubing
For track bars, upper arms, and lower arms that don't see harsh use
(sand is a good example), chromalloy tubing is a good selection.
Tubing measuring 1.25" diameter, .120 wall thickness, has the
same strength as thicker wall tubing but it is less resistant to
impact. It's light weight but high strength make it a good material
when weight is a consideration. Joints and adapters are available
for large and small sizes.
Control Arm Brackets and Spring Seats
Whether you're building a short or long arm suspension, triangulated
4 link or 4 link with track bar, with coil springs and shocks or
coilover shocks, there are a variety of components available. Many
can be used in multiple ways, offering greater flexibility in designing
Choices include lower arm brackets, upper arm brackets,
track bar brackets, and housing bridges. Lower brackets are
sized for the larger joints above, with spacer sleeves and
misalignment spacers for narrower joints. Upper brackets
are similar in design for joints up to 2" wide. All
brackets are laser cut and formed. Housing bridges span the
differential housing and are welded to the tubes on either
side, providing locations for mounting brackets or tabs,
limit straps or bump stops.
For coilover shock designs, Foothill has a selection of
tabs and brackets for axles, and bracket kits for use on
the frame. They accept all major brands of coilover shocks
For traditional coil spring and shock systems,
two approaches have been developed. For front axle applications,
the rectangular seat provides a mount point for a coil spring,
shock mount, and track bar mount. The coil spring seat can
be located where necessary to achieve the desired effective
spring rate. For rear axles, a rounded, foreshortened seat
ensures adequate clearance of arm mounts and shock mounts.
Spring and Shock Selection
Springs and shocks can be divided into two
categories. First is the traditional coil spring setup with
standard shock absorbers. As off the shelf components, they
are cost effective solutions that can provide excellent performance.
The choices however, are limited to "what you see is
what you get". You're limited by what manufacturers
have to offer for spring rates, lengths and diameters, and
shocks have fixed or moderately adjustable valving. Suspension
travel in these systems is typically limited by the length
of the shock used.
The second choice is a coilover shock design.
These designs offer seemingly infinite combinations of spring
rates and lengths and shock construction and valving. While
somewhat expensive, it is possible to tune a suspension minutely
and if desired, to the specific needs of each corner of the
vehicle. These components are also rebuildable. Coilover
shocks have longer travel than traditional shocks but also
require additional mounting space.
Suspension Travel Control
Four link suspensions have the inherent capability to allow damage
to occur to drivetrain and suspension components. Without some control,
it is quite possible to damage driveshafts, steering rod ends, shocks
or brackets. Bump stops should be used at critical locations where
damage might occur. A variety of choices are available, ranging from
air bump stops to competition style poly bump stops to hard, fixed
point button style stops. Over extension of a suspension can result
in the same damage--be sure to use limit
straps in the appropriate locations.
Sway bars are used to control body roll. On the highway, they provide
stability when cornering or traveling on rough roads. Off road, they
provide control of body roll on side hills, but at the expense of
suspension travel. Two fundamental solutions to sway control have
First is the factory sway bar that can be disconnected. This traditionally
has been handled with removable end links that permits the sway
bar to be swung up, out of the way, and secured. It is a simple,
easy way to gain suspension travel. The downside is the difficulty
in reconnecting the sway bar. Foothill has disconnects in several
lengths for this style of sway bar.
newer Jeeps, Foothill recommends the Tera
Street/Trail sway bar system. It features a stiffer torsion bar
for better on road handling, yet is easily disconnected with a single
turn of a knob. To re-engage the sway bar, simply twist the knob
to the street setting and drive away. It will automatically lock
A common pitfall that suspension builders encounter is selection
of springs that are too soft, thus mandating a sway bar to maintain
some control, even when traveling offroad. If the suspension has
been designed correctly, then a sway bar on the trail shouldn't be
The second solution is a permanently connected sway bar. These are
a compromise, in that there will be reasonable highway behavior,
but there will also be some limitation of suspension travel on the
trail. To help with tuning the ride and providing some choice of
sway control, the torsion arms typically have several holes for locating
the end links. Moving the end links will change the leverage exerted,
thus changing the amount of sway control. The biggest convenience
with this sway bar design is that there is no work involved to disconnect
or reconnect the sway bar.