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Foutz Motorsports
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Stewart Raceworks |
Some of the terminology associated with prerunners & desert race vehicles is pretty far removed from the mainstream of off-roading. While this is not a complete listing of all the terms associated with these vehicles, we hope it will further your understanding of them, and of the sport of off-road racing in general. Vertical Wheel Travel - Amount of wheel travel measured from the center of the axle at full droop to the center of the axle at full compression Lever Ratio - Shocks & springs can be mounted in several locations, and at various angles. If a shock were to be mounted vertically atop the axle, it would be said to have a 1 to 1 lever ratio - i.e. 1 in. of vertical shock travel = 1 in. of vertical wheel travel. If the shock is mounted at a 45 deg. angle, it will move 1/2 in for every inch of wheel travel. As such, it would be said to have a 1.5 to 1 lever ratio. 
Velocity Sensitive Shocks - Many prerunners
& race vehicles use velocity sensitive shocks. Their monotube
design is lightweight, affordable, and provides a significant "bang
for the buck".
VS shocks are rebuildable,
& use a series of stacked flexible washers to determine their
valving characteristics. Adjustments are made by disassembling the
shock, and changing the stack of washers to a stiffer, or lighter
configuration.
VS shocks use up to 200psi
of nitrogen gas to combat foaming at high temperatures & shaft
speed. further cooling capacity often comes from remote reservoirs,
though they are optional on most models. It is common to se several
VS shocks mounted together, and valved lightly, reducing the
workload per shock.
<>Coilover
Shocks - These shocks serve as a mounting point for a coil
spring. Unlike "overload" shocks found in auto supply houses,
"Coilovers" are extremely high performance units, used in 3 & 4
link suspension applications. The coil springs are removable from
the shocks for replacement & tuning, and the shock is fully
rebuildable / adjustable for compression & rebound dampening.
Coilover shocks are mounted to the chassis via spherical rod ends,
rather than bushings to minimize unwanted deflection, and provide
maximum streingth to the load bearing assembly. Coilover Shocks
most always come with a remote reservior to aid in fluid
cooling.
Remote Reservoir - Found on 9 out
of 10 race shocks, Remote reserviors provide the shock with
increased fluid & gas capacity, allowing for increased cooling,
less "shock fade", and longer maintenance intervals. These aluminum
& steel canisters contain a piston which separates the
hydraulic fluid from high pressure nitrogen gas. They are attached
to the shock absorber by a custom length of braided steel hose, or
high pressure hydraulic line, and can be attached anywhere on the
vehicle.
Bypass Shock - Bypass shocks are
the pinnacle of shock technology. The goal of a bypass shock is to
provide light valving in the initial movement of the wheel (to keep
the wheels in contact with the ground over smaller bumps),
progressively stiffer valving throughout the midrange of travel,
and finially very stiff valving at the uppermost reaches of a
shocks stroke to resist bottoming.
Using a
series (usually 2-4) of "bypass tubes" welded to the shock body,
valving becomes externally adjustable via metered "jets". The
bypass tubes provide precise oil flow through the shock, minimizing
cavatation due to heat or unequal pressure, and together with the
metered "jets", make for near infinite compression / rebound
dampening possibilities.
The latest
developments in bypass shock technology have led to the development
of "internal bypass" shocks. While the general principle of bypass
remains the same, internal bypass shocks locate the bypass tubes
inside the shock body, making them suitable for use in a coilover
configuration.
The sheer size of bypass
shocks is impressive, but they aren't built that way for their
looks. Rather than ounces, the fluid capacity of Bypass shocks is
better measured in quarts, translating directly into a cooler
running, nearly fade-proof assembly. Shaft sizes begin in the 7/8
in. range. Bypass shocks are always mounted via spherical rod end,
as the loads generated would quickly destroy rubber or ploy
bushings.
These are the shocks commonly
seen on (but not limited to) the Trophy, Pro & Class 7 & 8
trucks of SCORE.
3 Link
Suspension - the "link" in 3 link refers to the number of
mounting points on the rear axle. Used with torsion bar, 1/4
elliptic leaf springs & coilover shock arrangements, the 3 link
uses 3 "control arms" to locate the axle & position it as it
moves throughout it's range of travel.
The
standard configuration for a 3 Link is one arm (per side) mounted
slightly below the axle, with a forward attachment point at the
frame or custom built crossmember. Centered above the axle is a 3rd
mounting point, using a triangular shaped arm (usually built of
tubular steel), which attaches forward on the frame, or
crossmember. 3 Link suspensions have been built & tested with
up to 38 inches of "Vertical" wheel travel, and provide tremendous
amounts of wheel articulation.
Many
prerunners, and even some race trucks use bushings for the mounting
of the forward sections of the control arms, but the rear (axle)
mounting points are often spherical rod ends. The spherical rod
ends are a stronger assembly, and are less binding, offering a free
and greater range of movement.
4
Link Suspension - a 4 Link is identical to the 3 Link
except for using two upper control arms rather than one. these
upper arms are mounted from a near center position (each aside the
differential) and angled outward to the frame or custom built
crossmember. Like the 3 Link, The 4 Link is capable of incredible
vertical wheel travel, but articulation is slightly less.
A-Arm Suspension - usually found
on the front of non Ford vehicles, the A-Arm suspension uses an
upper & lower "A" shaped arm & a coil or torsion bar
springing.
A-Arms are a simple &
popular suspension, and can achieve respectable (aprox 13 in.)
wheel travel when used with stock length arms. On mini / mid size
trucks, wheel travel is limited by the shorter arms & can be in
the 9-11 in. range.
Long travel A-Arm
suspensions require longer / redesigned arms, and can involve
relocation of the engine / K frame to achieve sufficient clearance.
Further mods include spherical rod ends, modified ball joints, and
redesigned spindles. Depending on the configuration, travel in the
28in.range is achievable, but at far greater cost than other
suspension designs.
Twin "I"Beam - TIB / TTB suspensions consist of 3 main parts. The
I beam (which mounts the spindle / brake assembly), the radius arm
(which runs parallel to the frame, attaching at the I Beam in
front, and a crossmember in the rear), and the coil spring, or
coilover shock.
This front suspension has
been in use on Ford Trucks since the 60's, and has been
transplanted to just about every other vehicle in existence. The
reason for it's popularity is simple. There's an old desert saying
that says "12 in. of Ford travel is worth 15 in. of anything else".
Secondly, the cost of a 15 in. TIB or TTB system is well under
$2000, making it the best value per in. on the market today.
The Twin I Beam (and it's 4wd counterpart the
TTB-Twin Traction Beam) is a far stronger design than the
traditional A-Arm, and is ridiculously easy to extract usable
travel from. A stock F-150 approaches 10 in. of travel, & with
a few simple mods, 15 in. of wheel travel is there for the taking.
Extreme examples measuring in at 32 in. are not unheard of, but
26-30 in. is common in race vehicles.
Variations on the TIB can be found on such diverse vehicles as
Glamis bound sand buggies, Polaris & Yamaha snowmobiles, and
even the Toyota Land Cruiser that Ivan Stewart uses to prerun the
courses of the SCORE / Laughlin desert series!
1/4 Elliptic Suspension - 1/4 elliptic
suspensions use a 3 or 4 link configuration, and replace the
coilover springs with leafs.
An ellipse is
a full circle. 1/4 elliptic rear takes it's name from the shape
& configuration of the leaf springs, which, not coincidentally,
resemble the arch of 1/4 of a circle.
Mounting the leafs can take many forms, with a roller or
spherical rod end, being the 2 most common types. In the rear, A
pivoting "clamp" holds the springs in place, while a NASCAR style
"Weight Jack" allows the builder / tuner to adjust ride
height.
Torsion Bar Suspension -
can take many forms. Commonly, torsion bars are
used in conjunction with A-Arms in front suspension applications,
due to their simple design, ease of maintenance, and light weight.
TB suspensions are occasionally found in custom rear suspension
applications, controlling a 3 or 4 Link set up.
Torsion bars are often used to supplement coil or leaf
suspensions, acting as a "secondary suspension".
Secondary Suspension - Used most
often on race trucks & "top shelf" prerunners, secondary
suspension systems allow for very light primary springing (to allow
the truck to effortlessly absorb smaller bumps & obstacles),
and only come into play in the final inches of wheel travel. The 2
most common forms of secondary suspension are Pneumatic (air /
nitrogen) & Torsion bar.
Pneumatic Bump
Stop - Used in place of, or in conjunction with a poly
bump stop, pneumatic bump stops function similarly to an air shock.
High pressure nitrogen allows the stop to be tuned to a specific
degree of resistance, and some suspension set ups, can act as a
form of secondary suspension (by providing a dramatic but
controlled increase in effective spring rate during the last few
inches of travel).
Spherical Rod
End - AKA: "Hiem Joints". SRE's are a high strength
solution to extreme angle woes. Available in sizes from 1/8 in. to
well over 1 in. SRE's have found use at the ends of control /
radius arms, tie rods, A-Arms, and many other parts throughout both
prerunners & race trucks.
Recently,
aftermarket lift kit manufacturers have begun incorporating SRE's
into the Jeep TJ / XJ / ZJ model lines, as well as the Dodge
Ram.
Parker Pumper - While
Parker Pumper is a brand name, it has come to be as interchangeable
as "Xerox" in the off road community. The pumper is an air
filtration system consisting of a chassis mounted blower that ducts
filtered air to a specially modified helmet, allowing the wearer
breathably clean and cool air in the dusty desert
environment.
Suspension Seats
- Produced by several manufacturers, suspension seats
utilize an nylon/canvas "base" to cradle the foam padded seating
area. This "base" is in turn attached to a tubular steel seat frame
by an elastic cord, creating a seating surface that is "suspended".
Major advantages to suspension seating include smoother ride,
reduced potential for back (spinal compression) injury, and
improved vehicle control.
See our review of Beard
suspension seats
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