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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
vehicle. A mini-van can't be driven like that on the daily
to work. It's too bad that driving like that is so much fun
it won't take the new racer long (hopefully) to find out that hanging
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
weight percentages are reasonably close, the next consideration is
It has often been said that "tires are everything". I've said
a more than a few times myself. Of course there are many other
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
tread configuration, size or pressure. Whatever the case, if the
back end is sliding, the back tires aren't gripping. Volumes
be written about choosing the right tires and that is certainly
our intention at this time. There is one thing that I have
about tires over the years. If the tires are showing a lot of
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
cornors though. Just the ones that are getting hot and wearing
It is not uncommon for oval racers to use a harder compound for the
side than the left. If a tire is not showing any wear at all,
may not be working either. One exception is on very damp or wet
Quite often, karts that are very hooked up on that type of surface
wear the tires at all. If the tires are't showing any wear,
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: firstname.lastname@example.org