TOO LOOSE? TIGHTEN IT UP! by Mark Bergfelt
It's incredibly exhilarating to take a kart
into a corner real hard and throw it in causing the back end to go into
a wild slide. What a blast to be at the wheel of a high
performance
vehicle. A mini-van can't be driven like that on the daily
commute
to work. It's too bad that driving like that is so much fun
because
it won't take the new racer long (hopefully) to find out that hanging
the
rear end out is usually not the fast way around a dirt track.
It is desirable to be driving a kart that is
responsive
to the driver's input. When the driver turns the steering wheel a
little, the kart should turn a little in whatever direction the driver
wants to go. When the driver turns the wheel a lot, the kart
should
do likewise. When the kart turns as much, but only as much, as it
should,
without the back end sliding as a result, the kart is said to be
neutral.
This is desirable and is usually fast. When the driver turns the
wheel and the back end wants to slide as a result, the kart is said to
be loose. If the kart is too loose, the driver can't stay on the
throttle when negotiating what should be a fast turn with out
sliding,
or even spinning out, or has to slow down way more than he should on
tight
turns. It also means that the driver can't get on the hammer as
soon
either. Even if the driver can stay on the throttle but the back end
"hangs
out", this situation is still usually slower than if the back end
stayed
straight and followed the front. When the back wheels are sliding
sideways, the effect is very much the same as using the brakes.
The most desirable way to negotiate the turns
on a dirt oval is with the throttle all of the way on, the front wheels
turned just enough to get turned, and the back wheels closely following
the path of the front wheels without any sliding. Unfortunately,
(or fortunately if a challenge is what motivates you) many tracks are
just
too tight or the surface does not offer the grip needed to, to be
negotiated
in the ideal fashion. Having said that, still, a Briggs powered
kart,
on the majority of dirt ovals that I've visited, should be able to be
driven
flat out, most of the time. The number of tracks where a
two-stroke
machine or an open can go flat out are not as plentiful, but they are
out
there. What ever the machine, pedal-to-the-metal performance is
the
result of a good track and a properly adjusted chassis...and driver.
The question of the moment is, what can you
do if your kart is loose? Actually, there are quite a few
strategies
for correcting the situation. This article is actually the third
installent in a series. The first was "From Sprint to Dirt", NKN,
June 2000, and the second, "So You're Pushin'", NKN, September 2000
.and
now, this one. In the first, a suggested, "rule of thumb"
starting
set-up was discussed in detail. That article was intended for
sprint
guys who wanted to see what it was like to "do it in the dirt",
but
the information was good for any new dirt guy. If the guide lines
for an initial set-up are followed the new comer to dirt should not be
too far off. Sure, the suggested weight percentages of 40%
front/60%
rear and 60%left/40% right probably won't be optimum in all cases but
they
provide a good place to start. I hope the reader can get a copy
of
those two articles to get all of the details. The point is, if
the
initial set-up of the kart is not reasonably close, it will be
difficult
to fine tune.
Strategies For Tightening Up a Kart
After a racer has determined that his
starting
weight percentages are reasonably close, the next consideration is
tires.
It has often been said that "tires are everything". I've said
that
a more than a few times myself. Of course there are many other
factors,
but there is no doubt that having the right tires is at the top of the
list. If the back end of a kart is sliding, it could very well be
that the rear tires just aren't right. They may be the wrong
compound,
tread configuration, size or pressure. Whatever the case, if the
back end is sliding, the back tires aren't gripping. Volumes
could
be written about choosing the right tires and that is certainly
not
our intention at this time. There is one thing that I have
observed
about tires over the years. If the tires are showing a lot of
wear
and are getting feathered, they are definately too soft. Go to a
harder compound. You don't have to go to a harder tire on all
four
cornors though. Just the ones that are getting hot and wearing
down.
It is not uncommon for oval racers to use a harder compound for the
right
side than the left. If a tire is not showing any wear at all,
they
may not be working either. One exception is on very damp or wet
tracks.
Quite often, karts that are very hooked up on that type of surface
don't
wear the tires at all. If the tires are't showing any wear,
definately
try a softer compound and maybe even some tire softener.
In may cases, a kart is loose because it does not have
enough left rear weight. Many of the adjustmanet that are made to
a chassis to tighten up a kart are methods of applying more weight to
the
left rear tire. Increasing the diameter of the left rear tire
will
increase the percentage of weight that the tire carries. That
could
be the answer. It will also decrease the stagger which also can
help
tighten up a kart. If you have a weight jack on either of the
front
spindles, adjust it so that the right front is carrying more
weight.
This will also cause the left rear to carry more weight as well.
As many racers say, this will increase your cross weight. If you
don't have a weight jack, don't worry, adjustable king pin screws (if
your
kart is so equipped), or washers to make the adjustment. Another
way to increase the right front corner weight is to install a
taller/larger
diameter right front tire or smaller diameter left front tire.
This
is a good strategy for old karts that don't have adjustable spindles.
Karts have locked rear ends. Since both
rear wheels are turning the same speed they really would be difficult
to
steer if it were not for the castor and kingpin inclination built into
the front end of the kart. When the driver turns the wheel
to the left, the castor and kingpin inclination cause the right front
wheel
to lift off of the ground and shove the left side down. When the
kart is moving, and the wheels are turned to the left, the weight on
the
left side transfers to the right. This causes the right front
wheel
to stay in contact with the track and the left rear to lift
slightly.
If it does not lift enough, the kart will push. If it lifts just
enough the kart will handle just right. If it lifts too much, the
kart will be loose. With that in mind there are many adjustments
that can be done at the front end to tighten up a kart. They
are;
1. Pull the left front wheel in. It won't "jack" as much weight
off
of the left rear when you turn. 2. Decrease the castor on
the
left
side. This too will cause less weight to be jacked off of the
left
rear when turning. These two adjustments will have the most
effect
when entering a turn. 3. Pull the right front wheel
out.
This will increase the effect of the castor angle to transfer weight
back
to the left rear tire when the driver is countersteering. This
increases
a drivers chances of saving a kart that is spinning out. 4.
Increase the right side castor. This too will increase the amount
of weight that is transferred to the left rear wheel when
countersteering.
5. Use a wider right side front tire. This will have an effect
similar
to spacing the right front out. It may also provide more traction
to reduce drifting. 6. Use a narrower left front tire. The effect
will be similar to pulling the left front wheel in.
Tire pressure is important and is a subtle
but effective tuning too. To tighten up a kart with air pressure,
first make sure that you are using a pressure that provides the most
grip,
especially in the rear. Increasing the left rear pressure will
decrease
stagger, the difference in circumference between the rear tires.
Increasing the tire pressure will also increase the amount of load that
the tire is carrying. If you increase left rear tire
pressure
than you have increased the amount of load that tire can
handle.
Increasing the right front pressure will have a similar effect.
If
using this tuning variable, a change to a different wheel tire
combination
may be in order to maintain the original tire circumference at the
higher
pressure. The rationale of this tuning method comes from the use
of springs for tuning on full size cars. Generally, when tuning a
car with springs, stiffer springs at a corner will increase the load on
that corner. The springyness of the tire side wall can be used to
produce a similar effect.
The position of the rear tires is important
to how well the rear end sticks. Generally, pulling the wheels in
as close to the frame as possible will render maximum tightness.
If you don't already have the wheels pulled in all of the way, start by
pulling in the left side. This will vary somewhat from manufacturer to
manufacturer due to the variety or rear end frame widths. Karts
with
extreme left rear wheel offset can be pulled in too far sometimes and
may
not react the same way. Check with the manufacturer of the kart
for
their recommendation.
Many karts can be adjusted for more or less
flex. Here again is an area where the chassis manufacturer should
be consulted due to the variety of methods of adjusting chassis
flex.
Whetever the case, use the method that supplies the maximum rear end
grip
for the track conditions.
Sometimes a kart that seems loose is really
too tight. What I mean by that is that the driver senses that the
kart is tight, so he drives into the corner harder to break the back
end
loose. Once it breaks loose, he must regain the traction that was
lost. If he has trouble doing so, the kart will have the
appearance
of being too loose.
A driver that is not smooth will make a fast
kart appear to be loose. Rather than turning the steering wheel
just
enough to get the kart to turn, he will jerk it quickly when entering a
turn. This will cause the back end to break loose. All that
may be necessary in this case is to convince the driver to calm down
and
relax. This is often easier said than done. Another
strategy
that has been effective to counteract this situation, is to switch to a
larger diameter steering wheel. The larger wheel requires the
driver
to turn the steering wheel more. This is a good remedy for the
driver
who is tempted to turn in too fast or too soon.
Moving the seat toward the left rear corner
will bias more weight to that corner. That will help when the
kart
is loose. If you have to add ballast to make a minimum weight
attach
it near the left rear tire.
No matter what, if the reader is new to dirt
oval racing, one thing is certain, keep notes. No matter wht you
do, whether it works or not, write it down. That will help you to
remember what worked under a variety of conditions. It will also
remind you of what did no work so that you do not do it again.
Whatever
the case, even if your kart is loose, it's still a lot more fun to
drive
than that old mini van that you use for your commute to work.
To comment or ask questions, email the author: bergfelt@verizon.net