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Words: Jeff Huneycutt
They are really called anti-roll bars
because that's what they do, but only the most anal among us (Yeah,
we're talking about you over there.) actually calls them that. Most
people simply call them sway bars because we're just too lazy to get
the extra syllables out. Regardless of what you call 'em, sway bars
are a vital tuning tool when it comes to helping your car maintain the
proper attitude through the turns. This guide will help you develop a
process for determining when running sway bars will help you and
exactly what size best suits your needs.
What Does It Do?
The purpose of a sway bar is to tie the left- and right-side wheels,
either front or rear, together to help control body roll. For example,
as an RC car rolls through a left-hand turn, inertia forces the car to
roll over on it right side. If there is no sway bar, the right side
suspension compresses and the left side goes into droop, or extends.
With an on-road or touring car, this overloads the right-side wheel
and underutilizes the left, lowering the car's overall ability to
maintain traction.
Now let's add a sway bar to the scenario. As the car rolls through the
turn, the right side of the suspension compresses as before, but now
instead of the left side of the suspension going into droop, the sway
bar pulls the left wheel up. This limits body roll and actually causes
the car to settle down through a turn. The end result is actually to
lower the car's center of gravity, making it more stable.
 Tuning
There are two major types of sway bars used in RC cars today: the
formed-wire style and flat "blades." The wire style is more
common and traditional. It's the only kind you will find on off-road
cars and is also common on touring cars. It works by twisting and
providing a spring action as it untwists. The blade style sway bar
will usually only be found on touring cars where keeping the center of
gravity as absolutely low as possible is a priority. It works by
flexing, or bending the blade in a U-shape. Whichever one you use,
going with a thicker bar will increase the effect of the sway bar
while going with a thinner bar will reduce its effect.
 Also,
the type of car you drive will determine sway bar size. A lightweight
car with small, light wheels can get the same effect from a small,
seemingly flimsy sway bar as a much larger bar on a heavier car.
Because of its relatively heavy tires and wheels, a monster truck
requires a substantial sway bar to overcome the inertia in the weight
of the wheels.
Depending on your setup, you may not always want to run the same size
sway bar on the front and the rear. Heck, there may be times when you
want to run a bar on the front and not on the rear at all. There are
no hard-and-fast rules in this game, just methods for finding the
setup that works best for the conditions and your driving style.
Bars and Springs
The sway bar itself does not work independently; it actually has an
effect on the springs you should use. Because it ties the right and
left sides of the suspension together. As one side of the suspension
compresses it actually must overcome that spring and a portion of the
weight of the spring on the other side as well. Exactly how much of
the spring on the opposite side of the suspension is brought into play
depends on the thickness, or strength, of the sway bar. If the sway
bar is thin and flexible it will allow a lot of movement on one side
of the suspension with very little effect on the other. If the bar is
too thick or strong, it will effectively tie the two sides of the
suspension together so stiffly that it essentially becomes a
straight-axle suspension. The key is finding the right spot in between
these two extremes.
So finding the right sway bar size is critical, but it also involves
adjusting your springs to account for the bar. When adding a sway bar
to a suspension system, you generally will need to soften your springs
because now when one side of the suspension moves, the sway bar
activates both springs.
 On
The Dirt
When and how you run sway bars will have a lot to do with what type of
car you are driving and on what surface. In off-road racing a sway bar
is more critical on monster trucks than it is on buggies or stadium
trucks. This is because of the extremely high center of gravity on a
monster truck. A sway bar is used to control body roll which can
sometimes severely limit a truck's cornering speed. Install a sway bar
large enough so that when the truck begins to roll over on one side in
a turn, the bar pulls the other side of the suspension up so that the
truck both squats down and levels out. The center of gravity is
dramatically lowered and the ability to take a corner at speed
increases.
Without a sway bar the only way to keep a truck from rolling over in
the corners is to use extremely heavy springs. But doing this can
cause the truck to be difficult to drive in the rough stuff and even
bounce instead of absorbing impacts on landings. The beauty of a sway
bar is that it has no effect on the suspension on level landings. Run
the springs you need to land the jumps properly and depend on the sway
bar to help you get through the turns.
One trick with dirt-track racing to remember is that a certain amount
of body roll is necessary to maximize traction. Unlike on-road racing
where you want to get the most traction out of all four wheels, on
dirt you can take advantage of a controlled amount of body roll to
really plant the outside tires in a turn. Dirt drivers also are often
faster by "throttle steering," or using the throttle to kick
the rear end around in the turns. Because of this you don't always
want to try to achieve a totally flat ride through the turns like you
would on a touring car.
 On-Road
Issues
In on-road or touring-car racing -- especially if you are running foam
tires -- getting the most out of all four tires is critical. You can
get by with over-working the outside tires at first, but wear will be
accelerated and as the race continues you will probably find the
handling going away more quickly than the competition's. Watch your
tire wear. At the end of a run you ideally want both front tires to be
worn the same amount as well as the rears.
Sway bars can also be used to help you tune how your car handles. If
the car is pushing, or doesn't want to turn, decreasing the size of
the front roll bar can help. Likewise, if it is loose, or turning too
well and wanting to spin out on turn entry, stiffening up the roll bar
on the front can help reduce this.
The Drawbacks
The strength of a sway bar -- that it ties both side of the suspension
together in varying rates--can also be its biggest weakness on rough
tracks. On a smooth racing surface, the sway bar will affect a car's
suspension only when you want it to--in the turns. But on a rough
surface it can potentially cause more harm than good. That's because
if you hit a bump or rut with one wheel, a strong sway bar can also
upset the wheel on the other side of the suspension. This can cause
smaller bumps that are not a problem with a plush suspension to feel
much larger than they actually are if you are running a big bar. So on
rough tracks, try to stick with the smaller sway bar options.
CONCLUSION
Just like your temp gauge and screwdriver set, sway bars are a tool to
help you have more success with your racing. No one setting will work
in every situation, and what works for one driver's style won't
necessarily work for you. But now that you understand how sway bars
effect your car's suspension, you should be able to use them
effectively.
Source
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