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How to Un-Tweak Your Suspension
4 steps to a better-handling car
Words; DEREK BUONO
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The term
“tweak” originated with pan-car racers, but it applies to all
types of vehicles. While tweak setting is relatively easy to
understand and adjust on a pan car, on full-suspension vehicles it
can seem like a black art. A chassis is said to be “tweaked”
when it is warped, or when the suspension settings create the
effect having of a warped chassis.
Tweak
causes a car to corner better in one direction than the other, and
in extreme cases, it can even cause the car to pull to one side
under acceleration. Sometimes, tweak is caused by weight bias; if
one side of the chassis is significantly heavier than the other
side, the chassis will seem tweaked even if it is perfectly
straight and the suspension is set precisely. So how do you know
if your full-suspension touring or off-road car is tweaked because
of a problem with the chassis, the suspension, or weight bias? And
how do you fix it? Follow these steps:
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 STEP
1: Check the chassis for trueness
It's
best to do this before you build your kit. Remove the front
and rear suspension assemblies, and place the chassis on a
flat, level surface such as a kitchen counter. Push down
evenly on all four corners. If it rocks or one side lifts
off the counter, it's warped. If your car has a top deck,
loosen the screws; then press the chassis firmly down
against the counter and retighten the screws. If that
doesn't get the tweak out, it's best to replace the chassis,
but you could try to tune other areas to compensate for it.
Right:
Press down evenly on all four corners of the
chassis to check whether it is warped or whether
the top deck needs to be readjusted.
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Set
all the droop screws so the suspension has equal
downtravel. This is a key element in getting a
tweak-free car.
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STEP
2: Set suspension droop
You
can skip this step if your car does not use droop screws (also
known as down-travel screws). Disconnect the shocks so the
arms hang freely; make sure they can swing through their
range of motion without binding. If everything operates
properly, use the droop screws to set the maximum
down-travel so it is the same on both sides of the car.
Associated offers an inexpensive molded gauge that makes
the job easy; or you can buy a deluxe aluminum version
from Hudy. Just make sure your shocks are long enough to
allow the arms to reach maximum down-travel. That brings
us to the next step. |
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STEP
3: Check the shocks' lengths
Shocks
are your car's “legs”; if one of your own legs was
longer than the other, you would be lopsided. If your shocks
are of different lengths, your car will be lopsided. Use
calipers or a Trinity Shock Dyno to make sure the left and
right shocks are the same length and have the same amount of
travel. If they don't, you probably have the wrong number of
internal spacers in one of them, or one of the shock shafts
may be out of spec. Another possibility: you really goofed
up and used a rear shock body on the front suspension, or
vice versa. If the shocks are built properly, slight length
discrepancies can be eliminated by threading the shock
eyelet in or out.
Check
each shock length; they should all be the same.
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The
distance from shock mount to shock mount should be
the same on both sides.
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 Checking
for tweak
Now
that all the shocks are the same length and the preload
and droop are set, it's time to check the tweak. The
best way to gauge suspension tweak is to use a balance
system like this one from Niftech (shown on a Hudy
setting board).
When
using a balance system, set the gauge to level and place
the car's front wheels on the stationary bar; be sure to
center the car precisely over the pivot post. If the car
isn't tweaked, the pivoting bar the rear wheels are on
will remain level. If one side drops, that side of the
car is heavier, and the car is tweaked. To fix this,
recheck the shock length and preload settings; increase
the preload on the light side. When you're satisfied
with the adjustment, turn the car around and set the
front suspension tweak.
 A
scale system
measures the weight over each wheel and makes it even
easier to set tweak. But be warned: it's easy to become
obsessed with trying to make the left and right scales
read exactly the same, and it's virtually impossible to
do. Any change you make to one shock affects the weight
distribution to the other three. Get the numbers as
close as you can, but remember that races aren't run on
scales; they're run on the track.
And
that brings us to the most practical tweak test, which
is simply a figure-8 lap. Run a figure-8 with the
throttle steady and the same steering input from the
transmitter when you turn left and right. If your car's
turning radius is different for the left-turn parts of
the figure-8 than for the right turns, it's tweaked.
Likewise, if you know your steering servo's endpoints
are set properly, but your car spins out when turning in
one direction and pushes in the other, it's tweaked. A
tweaked suspension may also cause an off-road car to
pull to one side or fail to jump straight.
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STEP
4: Set the spring preload
Most
touring cars are set with zero sag: the suspension arms are
at full down-travel when the car is at rest. Preload is not
that critical for this type of setup, since it does not
affect ride height. But it is important to make sure that
the left and right shocks have the same number of preload
spacers and that they’re of the same thickness on both
sides. Threaded, or clamp-type, preload collars should be
set so that the distance from the top of the shock collar to
the bottom of the shock cap or top of the shock mount is
equal.
Off-road
cars are always set with some sag, and preload is more
critical here because it determines ride height. It’s good
to start with equal preload on the left and right shocks as
described above; but you may find that slight differences in
spring length, the amount of “set” the spring takes, or
the chassis weight bias requires that you increase or
decrease the preload on one shock to level the chassis.
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A
digital caliper makes checking preload easy.
Check that the springs are the same length on the
left and right sides. If they are not, adjust the
preload spacers to compensate for the difference.
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If
you don’t have any lead weight, don't
worry. You can use anything, including the
change in your pocket, to easily add weight
where needed.
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Weighty
issues
Most
kits are designed to be reasonably balanced with the
electronics installed, but a car’s components are
of various weights, so it will always carry more
weight on one side than the other. This can tweak
the suspension no matter how carefully you’ve
matched the droop, shock length and preload settings.
You’ll sometimes have to add lead weight to one
area of the chassis to compensate or make preload
adjustments to transfer weight from the heavy side.
Again, let practicality be your guide; if the car is
working well, don’t worry if there are a few more
grams on one side of the chassis than the other.
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| SOURCE
GUIDE |
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Associated
Electrics
3585 Cadillac Ave.,
Costa Mesa, CA 92626-1403;
(714) 850-9342;
http://www.rc10.com/;
http://www.teamassociated.com/.
Hudy Special Products
distributed by Serpent Inc. USA, West Park Center, 2830 NW 79th
Ave., Miami, FL 33122;
(305) 639-9665;
http://www.hudy.net/
info@serpent-usa.com
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Niftech
5565 Wilson Dr., Mentor, OH 44060;
(440) 257-6018;
http://www.niftech.com/.
Trinity
Products Inc.
36 Meridian Rd., Edison, NJ 08820;
(732) 635-1600;
http://www.teamtrinity.com/.
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Source:
Car Action
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