- Tweak is adjusted by tightening or loosening
the two tweak screws found on either side of the T-bar. You
should loosen the opposite screw first before you tighten the
first screw the same amount of turns.
- Using a good straight-edge lined up along the
center of the T-bar screws, you can find the exact center of
the pod. Just make sure the bottom of the pod plate lies flat
against the straight-edge and you can't miss.
- The coin drop method is the cheapest method
for checking tweak. In a nutshell, you scratch a mark on the
center of the cad widthwise ant the rear of the motor pod with
a hobby knife. Lift the rear of the car off the table on that
mark with a hobby knife blade. Check to see if either rear
wheel raises before the other. If they both raise at the same
time, your car has no tweak.
- A tweak board is a device that is specifically
designed to measure tweak. You place the car on the board and
the balance beam shows how much the rear wheels tweaked or not.
It is very simple to use and it is much easier to see the actual
amount of tweak than with the coin drop method. This tweak board
is from Niftech.
The Niftech tweak board stands out from
others for several reasons. The most obvious is the light and
compact design which can be packed away into a very small
package. It is manufactured out of U-shaped aluminum and other
metals pieces and durability should reflect this fact. A tweak
board such as this Niftech unit is probably the best
compromise of usability, portability, accuracy, and cost for
the majority of racers.
- The split tweak board places each rear wheel
on its own scale. This type of unit provides the ultimate in
accuracy but it ain't cheap. If you require no compromise tweak
accuracy, and the ability to measure actual wheel weights
regardless of the T-bar stock, the split tweak board is the way
to go.
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What is tweak? Well, it's easier to explain what tweak isn't. If
the wheels on the left side of the car push down on the ground the
exact same weight (corner weight) as their corresponding right side
wheels, the car is said to be not tweaked (twisted). A tweaked car
is one that has an imbalance to one or the other side. The amount
or degree of this imbalance is referred to tweak. A car that has
some degree of tweak will oversteer when turning in one direction
and understeer when going the other way. Naturally, one would
assume the best setup would be a car with no tweak. This is true
in most cases with the exception being for tracks where most of the
turns run in one direction such as oval racing, but we'll get to
that later.
Tweakin'
While any car can be tweaked, in the RC wold, tweak refers to
pan cars exclusively. Tweak is adjusted by tightening or loosening
the two tweak screws, found on either side of the T-bar. When you
tighten one tweak screw, you should loosen the other screw to
remove the tension created. (Actually, you should loosen the
opposite screw first before you tighten the first screw the same
amount of turns, but you get the idea.)
To Tweak or Not To Tweak
WHich screw you need to tighten and which screw you need to
loosen depends on you desired results. As I mentioned earlier,
for road courses, having no tweak is desirable. For oval racing,
tightening the right (as seen from the rear of the car) tweak
screw will produce more understeer (push) in left-hand turns,
and more oversteer in right-hand turns. This reduces the oversteer
tendency and seems to take some of the "twitchyness" out of oval
pan cars. This is like setting "the wedge" in an independent rear
suspension car. (We'll discuss the wedge and other handling topics
in the near future.) Alternately, tightening the tweak screw on
the left side will cause the car to understeer more to the right,
and oversteer more to the left. In other words, reduce push. I know
this can be confusing. A good way to remember about which screw does
what is to think of it like this. To increase push, push
(tighten) the tweak screw on the opposite side.
Now armed with this information, the problem becomes how much tweak
do you need or don't want. Unfortunately, I can't give you any exact
numbers since tweak, like other car setup variables, isn't an
isolated adjustment. Track conditions, the equipment that you use,
the way that your car is setup, and your driving style will dictate
how much tweak you'll need. If you're not looking for zero tweak,
you're going to have to just experiment to find out what is good for
you.
Checkin' Tweak
Currently there are three methods for checking tweak. Two of
these methods allow for tweak measurements. Also, the cost of each
method rises with its capabilities. Which is best for you depends
on what your requirements are. We'll discuss each method and their
pros and cons. Once you get an idea of what's what, you'll be able
to decide which method is right for you. When using any of the
methods listed below, check tweak with a fully loaded, race-ready
car.
Coin Drop
This is the cheapest method for checking tweak and the most
widely known. Basically, what you do is scratch a mark on the
center of the car widthwise at the rear of the motor pod with
a hobby knife. Then place the blade exactly on that mark and
lift the rear of the car off the table. While lifting the car
off the table, see if either rear wheel raises before the other.
If they both raise at the same time, your car has no tweak. While
it is fairly good for checking for zero tweak, as you can imagine,
it can't do anything more than that with any type of accuracy.
Here's a tip. Most people will tell you to measure the exact center
of the motor pod, by dividing the distance between the outer edges
of the rear wheels. I've found that if you use a good straight-edge
lined up along the center of the T-bar screws, you can find the
exact center of the pod. Just make sure the bottom pod plate lies
flat against the straight-edge and you can't miss.
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Tweak Board
A tweak board is a device that is specifically designed to
measure tweak. Most have a large stationary platform for the front
wheels and a pivoting bar or balance beam for the rear wheels. You
place the car on the board and the balance beam shows how much the
rear wheels tweaked or not. It is very simple to use and it iw much
easier to see the actual amount of tweak. The standard way to
measure tweak was via some markings on the board used to measure
tweak angles.
A recent entrant into the tweakboard market is from a company called
Niftech. The Niftech unit stands out from the others
for several reasons. The most obvious is the light and compact design
which can be packed away into a very small package. It is
manufactured out of U-shaped aluminum and other metal pieces. This
is a mejor departure from the standard wood tweak board and
durability should reflect this fact. Another difference is that
the Niftech unit uses a bubble level for its measurements.
Whle this may seem to be lacking in accuracy, Niftech claims
a 3-5 gram accuracy. Needless to say, a tweak board (any tweak
board), is a major improvement over the coin drop method.
Split Tweak Board
On the high end of the scale (no pun intended), we have the
split tweak board. This method uses a tweak board designed for
the front wheels of the can and two digital scales. (Analog scales
aren't as sensitive and are generally harder to read.) This type of
unit provides the ultimate in accuracy. There is no better method
for measuring tweak. It is also the easiest to use because you can
read the digital read out easier than you can read the print on
this page.
So why isn't everyone using this method? The price is very high.
This is due to the costs of the scales (approx. $80-$120 each) and
the cost of the board itself. THe board must be absolutely flat,
and the scale platform must by absolutely parallel with the board
face. Craftsmanship like that doesn't come cheap.
Here is one question that frequently comes up. If two scales are
good, wouldn't four scales (one under each wheel) be better? At
first glance, you would think so. but the truth is, with four
scales, it would be difficult, if not impossible, to determine
how much was tweak and how much was actually weight distribution.
Good question though!
Conclusion
So there you ahve it. Each method has its strengths and
weaknesses. The coin drop method is cheap (for all intents
and purposes, free) because it doesn't require any additional
hardware than what you probably have in your toolbox already.
However, its usefulness is limited to checking zero tweak and
its accuracy is highly user dependent. Accuracy depends on your
hand/eye coordination.
The Niftech tweak board allows for accurate and repeatable
tweak measurements. It is easy to use, an can comfortably fit into
a toolbox. The drawbacks to this method are that it's not cheap
(not expensive either), and can't take into account the use of
T-bars of different thicknesses. Since each rear wheel is coupled
together on the balance beam, even though you measure the same angle
of tweak, this won't measure how much weight each wheel actually
carries if you check a thicker or thinner T-bar. For instance, a
thicker T-bar will carry more weight on the lower wheel than a
thinner T-batr set at the same tweak angle due to its lower
flexibility. Nevertheless, a tweak board such as the Niftech
unit is probably the best compromise of usability, portability
accuracy, and cost for the majority of racers.
If you require no compromise tweak accuracy, and the ability to
measure actual wheel weights regardless of T-bar stock, the split
wheel tweak board is the way to go. It can reproduce a cars tweak
settings extremely accurately. This is a gret help if you do major
damage to your car (not due to a handling problem of course) and
want to reproduce your settings. The drawbacks are the size and
weight of the unit and its high cost. But then again, the best
usually costs more. Unfortunately in this case, that is definitely
true.
Have fun and be fast!
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