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Last Updated
February 8, 2004 7:41 PM


These are some of the guidelines for Grooving and "Siping" tires

The one thing every racer has to remember is that the tires are the only link between the chassis, engine and track, and an otherwise perfectly set up race car can not perform up to it's potential.

Dirt racers have to pick the right tire compound much like an asphalt racer, but there is another important step to getting the most out of a dirt tire. Dirt racers often have to alter the design of a tread pattern to best work with the conditions at a particular track, on that day and with their driver's style or habits. We can't tell you exactly the specific kind of grooving that will work best for your situation, but we can provide basic information to make you better able to decide for yourself as you encounter different racing conditions.

We also have to consider the abrasion of the track, how wet or dry the track is and if the track contains rocks or other debris that will tear up the tire. All of these conditions must be considered when deciding on what kind of groove to use, how deep to cut and how many grooves can be out without causing the early demise of the tire. Along with these factors racers must consider the amount of heat a track puts in their tires. In addition to enhancing traction, grooving helps the tire dissipate heat and can be used to help control tire temperatures.

Grooving and Wear

Any time a groove or sipe is cut into a tire it accelerates wear. The trick is to balance the benefit of grooving with the increased wear. One of the reasons we sipe a tire is to prevent the tread surface from glazing over and becoming slick. Sipes keep the surface wearing and the tire working throughout the race.

Learning to recognize the amount of wear you can expect from a track not only helps you choose the right compound tire for the night but is important information for deciding what pattern and depth grooving to use. The object is to maintain the highest level of traction throughout the race without wearing the tread off of it with five laps to go.

With an understanding of the basics of grooving tires racers will be able to look back on their experience with the tracks they have raced on and make better decisions on what type of grooving will help them most. Keeping records of the results of your decisions is the best teacher, so if you are not already keeping a "book" on each track, start one now.

Soft Tires

Racers rarely run soft tires in a race, especially the 100 lap events, but grooving soft tires correctly can be a big help in qualifying or short heats on a wet track. Softer tires are generally used on tracks that have a lot of moisture but not a lot of abrasion. You may also use a soft tire on a surface that does not generate a lot of heat in the tire and may have loose dirt or clay on the surface throughout the race. Cutting more grooves can help clean away loose dirt, plus improve traction because of the increased number of edges available to dig into the tracks surface. On tracks where you are not moving or throwing any dirt, but the surface is still relatively soft, a soft tire can often be run effectively with little or no grooving at all.

Keep in mind that grooving not only increases traction, but increases the rate at which a tire wears. A soft tire will begin losing it's traction sooner as the amount of grooving increases. The softer material naturally tears easier and fatigues sooner, causing the tire to slow down. On a surface with a lot of traction or if it contains rocks and other debris, the tire will tear up much quicker with excessive grooving. Determining the correct amount and style of grooving comes with experience and watching how the tire wears and what the driver felt s the race goes on.

One of the things we do with soft tires is only groove about half way across the blocks to prevent weakening the structure too much. With the large stagger block tread design we can often run that tire with little or no additional grooving, depending on the condition of the track. Usually we will run that pattern on all four corners on a wet track.

Occasionally when we run a ribbed tire on the right rear and do the grooving ourselves, we will follow the groove lines the factory put on the tire and then wait to see if the tire is going to start tearing and how many laps it takes for the tire to start working well. If the tire needs a couple of laps before it starts working we may add some grooves or sipes to give the tire a little extra grab until it develops enough heat to work on it's own.

Hard Tires

Though some harder tires may withstand grooving better than the soft compounds, the track conditions that made you choose a hard tire may not require much in the way of grooving. In the South we often do not groove the harder tires much at all. In fact, there are some tracks that pack down to where they are similar to asphalt and we have run tires with no grooves at all. We leave the tires full slick.

Grooving the Tread "Shoulders"

Grooving the shoulders can be helpful if you plan to run the high line or on a cushion and need to be moving some dirt. Grooves on the shoulders help clean away some of the loose dirt to get at moisture beneath it. Sometimes the outer row of blocks is also grooved on the right rear to work with the shoulders.

On some of the harder natural rubber tires we sometimes sipe the shoulders. This can really help when you are rolling the tire under when running lower tire pressures on a very slick track. The sipes can help prevent the shoulder area of the tire from glazing over and losing traction. The shoulder is as important a part of the tire as anything else and if you are going to be running on it due to low air pressure or because you are running against the cushion you need to make the best use of it.

Grooving Widths

Some tracks do not have a lot of abrasion to them and edges on the tire can increase traction considerably. When we get on a surface like that we will use wider grooves to present a cleaner, more prominent edge to the racing surface. Narrow grooves may not have enough distance between edges to allow them to work properly.

On some tracks you can groove the tires twice as much with a narrow groove, or half as much with a wide groove and accomplish the same thing. It depends on the track surface and how abrasive it is or if it contains rocks that will tear the tire up. You don't want a lot of grooves on a rocky or highly abrasive track. Fewer, but wider grooves stand up to these harsher conditions better.

Shapes of the Grooves

There are three basic shapes used in grooving: square, V, and sipes. Square grooves are the same width through it's entire depth. V grooves start out wide at the top and taper to nothing at their bottom. Sipes are thin slits cut by installing the blade upside down in the holder and using the separate ends of the blade to cut slices in the tire.

All three types of grooves can be used in various depths depending on conditions and the length of the race. The V groove is often used when the track is expected to need more tread contact later in the race. As the tire wears, the grooves become smaller or disappear completely. Square grooves can be used the same way but the extra width could provide enough leverage for an abrasive track to tear the tire if the track becomes abrasive.

Siping is usually meant to make the tread more pliable and does not produce the edges square or V grooves do. Siping also helps the tread maintain a more consistent wear that helps keep the tire working uniformly.

Grooving Angles

The angle at which grooves are cut determines how much of the edges are exposed to the track when the car is in various degrees of slide. Dirt race cars seldom if ever run in a straight line but the driver will try to keep the car much straighter when the track is slick than when there is a lot of bite to work with. When the track is slick we keep the grooves pretty straight. But when we spend a lot of time with the car sideways we put more angle into the grooves.

How much of an angle is dependent on the drivers style and experience is the only way to determine the best angle for your situation. The idea is to keep the maximum amount of the tires edges facing the direction the tire is actually traveling. As a dirt car travels around the track on a given line, the body is actually pointed towards the infield a certain number of degrees. If the driver is consistent you can determine an angle for the tire grooves that will work best for your combination.

Circumference Grooves

We almost always cut circumference grooves in our front tires because they help make the tread blocks more flexible which increases traction and helps the steering. Here also the width of the groove is determined by individual track conditions.

At some tracks we will also sipe across the circumference grooves so that we are making little blocks that are more flexible yet. These smaller blocks can help a lot when you catch little rough areas on the track.

Rough Race Tracks

We have found that as the roughness of a track increases, so does the need for grooves. Unless the track surface is very smooth, some sort of grooving is likely to be necessary to be fast. When you groove a tire more, it makes the tread surface much more flexible. It can then follow or shape itself to the surface much better to provide the maximum amount of bite possible.

Grooving and Heat

Some tracks naturally put a lot of heat into a tire and can actually cause the tire to melt or blister. On these kinds of tracks we have found that grooving helps cool the tire. The grooves (and sipes) help move air across the tires surface which keeps the tread temperatures down. Grooving also produces more surface area which helps transfer the heat out of the tire to the air. You have to balance grooving with the amount of abrasion or traction available because tracks that generate a lot of heat may also be very abrasive or contain rocks that want to tear the tire up if it is grooved too much. Too much grooving or siping on a high traction (or abrasive) track can cause the tire to start tearing up very early in the race.

To help a tire dissipate heat without weakening the tread blocks too much we will cut grooves in the center of each block instead of cutting all the way across it. We have even made a tool for drilling a circle in the middle of individual blocks to help cool without weakening the blocks structure too much. This kind of grooving works well when you want as few grooves as possible for speed but need to increase cooling to prevent blistering.

Race Length

The number of laps to be run is an important consideration when deciding how to groove your tires. Softer tires may be used in shorter races of 25 to 40 laps and you will have to be careful about removing too much rubber which may cause the tire to wear out prematurely. Accelerated wear caused by excessive grooving can be a problem with harder tires normally used in 100 lap races depending on how abrasive the track is.

We try to decide how much wear we expect on a particular track, then adjust our grooving accordingly. Often we will groove only half way into the depth of the tread so as the races progresses and the track turns smooth and abrasive normal tire wear produces very shallow or grooves that begin to disappear. Then when we need the most rubber on the track, the grooves are just about gone.

Keeping Records is VITAL

Learning the tracks on which you race and how they change over the course of an evening of racing will go a long way in helping you learn to groove tires. Keep track of how your last grooving ideas worked with the condition of the track surface. What were the other guys doing that drove past you? Read your tires after the race to see if another style or amount of grooving would have worked better, then write it down so you will have that information the next time you are in a similar situation.

Much of learning to prepare and drive on dirt surfaces comes from experience and applying that information to your current situation. You may spend some time writing down what DIDN'T work, but that puts you closer to what WILL work to make you faster

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