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STAYING HOOKED...READING DIRT OVALS by Mark Bergfelt
"How hard can it be? After all, all
doing is going around the same circle over and over again. It
take that much effort and skill to get around a dirt oval track in a
as fast as it can possibly go, should it? After all all of those
"go-carts" are just about the same anyway...and you all are using the
kind of engines. So what's the big deal? All you've got to
do is drive."
Over the years, I've heard many of the above comments, and if you have been a dirt karting enthusiast for a least a week, you've heard some of them too. Another way to spot the "uninformed" about our sport is by their insistance on spelling kart with a "c". But that's the subject of another editorial. This article is intended to help you get around your local dirt track quicker and keep you going fast not just in hot laps, (fast laps, practice, whatever) but in the feature as well.
Just spend one day or evening at a dirt oval event and you will surely see that although the dimensions of the racing surface do not change during the course of an event, often times the feature event is staged on a much changed track. Sometimes event the dimensions of the track are altered. Some promoters like to block off the inside groove with cones until feature time so that that portion of the racing surface does not dry out before the main event. Personally, I hate when they do that. The moisture content of the clay or dirt track surface has EVERYTHING to do with what YOU have to do to get a grip and stay hooked up. How much effect the moisture has will be determined by the composition of the clay or dirt, and the time of day that the event is staged, as well as the weather. The racer who can "read" the track and anticipate what it is going to do, will not just have an edge on the competition, he will have the key to victory.
Changes in track conditions may require tire compound or pressure changes, chassis adjustments, movement of weight on the chassis, gear changes and more to stay hooked up to the track. It is not uncommon for someone to be flat out flying on the wet track in fast laps only to not be a factor in the feature. The opposite is also true. The driver who is slipping and sliding in practice, may end up the feature winner because the "track came to him".
It's all about traction. It's also about getting the right balance of traction. The right amount of front traction will insure that the steering is neutral. That way the driver can go where he wants whenever he wants. Too much front bite and the back end will be loose. The right amount of rear bite will get you off of the turns straight and true, with out spinning, but too much rear traction can cause an unmanageable push and even wheelies on high horsepower karts. Too much right side traction can cause a kart to bicycle. This is really rare on dirt but can happen. Just the right amount of side bite will allow the driver to go "pedal-to-the-metal" all of the way around the track.
It would be nice if there was some type of electronic gizmo that you could stick into the track, something like a tire durometer, and it could tell you what tire compound to use. If this suggestion sparks the imagination of some electronics genious out there, then I get the first one free, but as far as I know, no such device exists, yet. You have to learn that art yourself.
Dirt and clay is different everywhere. Just the color of the substance reveals that there are differences. Usually these variations are due to geographic region differences. The folks in the South East are blessed with that bright red clay. I havn't had much of a chance to race on it but I understand it's really good. A little farther north it gets a little browner but it's great just the same when it's prepared properly. Here in Pennsylvania the clay ranges from gray to yellow as well as reddish. One track in South Eastern Ohio has a dark colored clay with sand mixed with it. The point of all of this is that there is a vast difference in the substance that makes up the surfaces of dirt tracks.
Often times the dirt base that exists on the property on which a promoter wishes to build a track is absolutely no good for a racing surface. In that case clay is trucked in. How much is added and how it is distributed and joined with the base has a lot to do with the quality of the final track.
Some promoters have a dust problem. This is usually but not always the case with tracks that are run during the day time, especially in hot, dry weather. Of course water is added to help control the problem, but sometimes that's not good enough. Some promoters add a special concentrate to the water formulated for the purpose of bonding the clay and retaining moisture. Some of these work well and enhance the grip that kart tires get. Another additive that is common is calcium chloride. This is commonly used in parts of the country that get alot of ice and snow to melt that stuff that gets on driveways and sidewalks. Not only does it melt snow, but it also attracts and absorbs water. When mixed with the water and added to the track surface, it helps the clay stay moist. If you race on a track that is treated with "calcium" be sure to wash it off immediately after racing. The chemical is hard on paint and will cause any unpainted components to corrode very quickly.
An inexpensive additive that some promoters use to bond clay so that it doesn't dig up or get dusty is liquid soap. Although it will successfully cut down on dust, and keep the track from breaking up, the surface will usually be very slick sndit will be very challenging to get a grip.
Back in the late 70's I remember racing at Dusty Valley Speedway in Eastern Ohio. The name of the track described the conditions there. One method that they found to control the dust was to put old motor oil on the track. The track got like asphalt. I don't think the EPA would permit that anymore, but it did control the dust problem.
It is always a pleasure to race on a SMOOTH track. Personally I don't care if it's a 1/10th mile bull ring or a 1/4 mile "super speedway", I enjoy a smooth racing surface. My greatest pet peeve, is rough race tracks. I don't mind BUMPY tracks that you maybe can feel a few bumps, ones that don't have an effect on what direction you are traveling or cause the seat to hurt your back and ribs. A ROUGH track will cause you to partially or completely loose directional control of the kart. It can cause you to partially or completely get airborn. This is extremely hard on equipment and the driver's body. The bigger and faster a track gets, the more brutal a rough track can be.
The relative smoothness or roughness is one dimension of a track's surface condition. Two other dimensions are the relative moisture content, ranging from wet, to damp and to dry and its relative hardness ranging to sloppy and soft to hard and abrasive. I prefer to classify racing surfaces as follows; wet/sloppy. wet/soft/tacky, wet/slick, damp/hard, damp/hard/abrasive, dry/dysty, dry/hard/abrasive, dry/hard/ slick. Combine these conditions with the dimensions of the relative smoothness of the surface and we wind up with a huge variety of possible conditions to deal with.
What's a racer to do? Don't forget it's all about getting and maintaining traction. It can be very challenging to match the equipment combination to the track surface condition, but there are some guidelines. If your chassis is scaled out pretty close and all of your steering angles are working reasonably well, most of your adjustments can be made with tires although other adjustments can be made as well to fine tune your kart. Please refer to "How to Make a Kart Hook Up on Dirt", N.K.N. February, 1996, and "Getting Set Up for a Dirt Track That You've Never Raced On", N.K.N. June 1996, for a detailed discussion of many of the adjustments that can be made to a chassis.
Over the years I have developed a personal preference for Burris tires for dirt racing. Burris took dirt racing serious long ago and has been the leader in developing compounds, sizes and tread designs that work on dirt. Most of my experience is with that brand so I'll limit my discussion to that product. I'm sure other brands work well also.
A durometer is a useful tool for determining the relative hardness of tires. The hardness or softness of a tire is important for matching the tire to the conditions. It is also useful for determining how much a tire has hardened due to age or use or how much it has softened due to heat or a chemical tire preparation. It can be very helpful when comparing one brand of tire to another.
The softest tires that Burris is currently producing durometer around 38. These are the K-21 and D-21 compound. The K indicates a treaded tire and the D designates a slick. The tread on the slick is thinner than the treaded tire. These tires work well when the track is wet or if the track is damp/slick. The next hardest tire is the K-O which durometers around 41 to 43. This is a popular where treaded tires are allowed. It is good on wet tacky tracks and is a good damp track tire. It may be too soft for damp/abrasive surfaces. K-1 and D-25's are slightly harder with a durometer reading around 44. They too are best suited for damp track and can withstand more abrasion. T-2's are a treaded design that is only slightly harder than the K-1 and will work in similar applications. If a damp track is very abrasive or when a track is dry but not abrasive, a k-4 or D-4 is often the answer. When tracks are very dry/hard and abrasive, an asphalt tire such as a M-30, which durometers around 58, an M-22 (or M-15B or M-20) with a durometer reading around 60, might be the answer. On very hot, dry and abrasive surfaces, especially in long races on high horsepower applications, an M-15A with a durometer reading around 70 has even been know to work from time to time.
One item that should be in the tool box, or at least the wish list, of every serious dirt racer is a tire durometer. A durometer almost looks like a pocket watch with a small flat spot that has a short, spring loaded metal point in the center. To use it simply stick the point into the tire tread and read the dial. Take several readings across the tread and around the tire. You will probably find that the readings are not identical but they are within a few points of each other. Consider the hardness of the tire to be the average of the observed readings. Also note that all durometers may not be calibrated the same. For that reason it is best to get your own durometer. If you must borrow, borrow from the same person all the time, that is if he doesn't get tired of you asking.
Tire pressure can also be a factor. The trend seems to be, the lower the better. You really only need enough air to keep the tread of the tire completely in contact with the track and the tire on the rim. Less air increases the rolling resistance of the tire, often this can translate to an increase in traction. Low tire pressure can be the cure when karts bounce on rough tracks.
If you go lower than the pressure that results in the desired traction, you are needlessly making your engine work harder, thus slowing you down. Excessively low tire pressure will cause the tread to roll under. It is helpful to have a helper observe the kart in action to see if this is the case. Add air to correct the problem. Low tire pressures can also result in bottomed out drive sprockets and related problems, which are costly and simply no fun at all. Tires can also be unseated from their rim bead. That can be very dangerous.
Pressure can be used to adjust a tires diameter. More air simply makes a tire bigger. Making a tire bigger is exactly the same as taking teeth off of the axle sprocket. The relationship is roughly one tooth per inch of tire diameter change. Air pressure is also a very easy way of adjusting stagger. Add rear stagger to help a kart that is too tight, ie., it's pushing. Take stagger out to tighten up a kart.
It is important to be able to anticipate what is going to happen to a track's surface during the course of race evening. On hot dry days and nights during a drought you can expect the track to dry out and perhaps be hard. Harder, slick tread tires might just be the ticket. If it rains between heats, and the promoter gets the track run in just before your feature, soft grooved tires will be a safe bet. Cooler weather will generally require softer tires and harder tires will get more use in hot weather. It is not uncommon to run a very soft tire for practice, right after the track has been watered and run in, a little harder tire for the first heat, slightly harder for the second and maybe even harder for the feature. For evening shows, though, don't be surprised if the fast guys switch to softer tires for the feature after running hard tires in the heats. They expect that late at night, when the sun is out of the picture and things cool off, the moisture will come up out of the clay turning what was a hard dry surface into a wet a slick one. High humidity on what was a rain free day can contribute the above scenario. Pay attention to the weather man.
Slight gear changes can also help racers maintain their hooked up status. If your gearing is close to optimum under a condition you are used to, then remove a tooth or two when you expect the track to get slick. That will reduce the tendancy to spin the tires off of the cornors. If you anticipate the track to be very heavy, or tacky, try adding a tooth or two. The extra bite in the cornors may lug the engine if you don't.
Is that really all there is to it? Absolutely not! The fact that there are so many variables to dirt racing is what makes it challenging, sometimes unpredictable, and always fun. Just always remember, don't let anyone get away with spelling kart with the letter "c".
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