Which part of your race car talks to you more than those four blackdoughnuts? They may not look like much, but they have a lot to say abouthow your car is handling. Teams that know how to take advantage of thefeedback the tires provide have a distinct edge over those teams that donot.
Do you start a race with lower pressure in your tires, in hopes ofbuilding heat after a few laps? If so, will you experience excessivewear in the process and risk a failure? Understanding the tires' roleand how to manipulate it to your advantage is critical to the setup andoverall performance of your race car. We spoke with Race Tires Americaand Shanon Rush and Craig Cowan of Hoosier Tire to find out the top tipson what every dirt track racer must know about dirt tires.
This tip may seem obvious, but a lack of attention to air pressure cansignificantly affect your race car's performance. According to Cowan,air pressure significantly determines dirt tire characteristics.
Air-pressure adjustments are...
Air-pressure adjustments are the easiest way to affect changes (good orbad) to your race car's handling.
"Because they are bias-constructed, air pressure determines the majorityof the spring rate within a tire. Therefore, it is imperative that tiresare treated just as any other part of the car setup," he explains. "Toomuch air pressure generally makes the car loose off the corner, whiletoo little air pressure gives the car a tight feeling on entry. Unlikeasphalt tires, it is not as crucial to balance tread wear across theface of the tire with air pressure. Concentrate on using air pressure toaffect the behavior of the car, not the tread wear."
The task of compound selection is complicated when you consider trackconditions and driver preference for a particular compound.
"This is by far the hardest part of tire management to master," saysCowan. "Selecting the proper compound depends so much on reading theracetrack and knowing what your driver likes; it often takes years tofind the proper combination."
According to Cowan, it's smart to begin with the basics: one soft, onemedium, and one hard tire. When the track is greasy, wet, or cold, runthe soft tire. Switch to the medium tire when the moisture disappearsand gives way to dry, slick conditions. When the dust is gone, so is themedium tire, so bolt on the hard one. Once you have a handle on thethree types, check out the in-between compounds for certain clay typesor wear patterns. Most importantly, take good notes on your choices tomake the selection process easier the next time.
"When in doubt, don't be afraid to ask the local tire dealer or trackchampion for their recommendations," he adds.
This can be built into a bias-ply tire by adding air pressure andincreasing the circumference, which aids in turning the race car. Or,buy a tire set with a certain amount of stagger already built in.Hoosier Tire features a marking system that enables racers to choose,from a pile of tires, the stagger they need without mounting three orfour sets.
Stagger is the difference...
Stagger is the difference in circumference of two tires on the same endof the car. Measure around each tire near the middle of the tread.Subtract the two measurements to find stagger or "roll out" as it'ssometimes called. Always inflate the tires to race air pressure beforemeasuring.
"The key is to remember that the marks are not what the tire willactually measure," advises Cowan. "They are guidelines to assist inpicking the proper tires. As a general rule, right-side tires willrollout 2-21/4 inches smaller than the mark, while left-side tires willgo 3-31/4 inches below the mark size. Air pressure is the main factorthat determines how much size differential you see from the markedsize."
This simple tip will have a significant impact on the amount of biteyour race car will get.
"A sharp edge is always more effective, no matter the track condition,"Cowan says. "Most of a tire's traction capabilities come from leadingedges of blocks (tread) grabbing the track surface and pushing the carforward. If an edge is sharp, it bites harder. If not, the edge slipsand limits forward traction."
He adds that to get fresh edges, grinding tires is a smart alternative,because it reduces loose rubber and dull edges that break contact withthe track. Another advantage is that it freshens the top layer of rubberon the tire, so it fires quicker on restarts.
This is an area in which you have to figure out what tirecharacteristics will benefit you the most, depending on your race car'ssetup.
"Our rib tire (only circumferential grooves are molded in) isconstructed softer than our LSB (Large Stagger Blocks molded in), so youalways know which tire you have," explains Cowan. "We have found overthe years that softer tires make the car tighter through the middle ofthe corner while stiffer tires loosen the car at the same point."
Tires, as tough as they may look, are quite sensitive to weatherchanges. Keep your tires out of direct sunlight and excessive moisture,as these may cause cracks in the sidewalls and ruin the tread compound.
Although choosing the right tire compound is important, the ability tomanipulate the tread pattern to suit your needs for a particular trackor set of conditions is just as crucial. When done correctly, groovingcan help you get better traction and allow your tires to dissipate heat,which allows you more control over tire temperatures. Cowan and dirtLate Model driver Scott Bloomquist compiled the following.
* Grooving Soft Tires: While not common in longer races, groovingsoft tires may be effective for qualifying or short heats on a wettrack. Softer tires are generally used on tracks that have a lot ofmoisture but not a lot of abrasion. Loose dirt can be cleaned off bycutting more grooves, which improves traction because of the increasednumber of edges available to dig into the track's surface. To preventweakening the structure, only groove about halfway across the blocks ofa soft tire.
* Hard Tires: If you plan to run the high line or cushion andneed to move some dirt, grooving the tread shoulders is helpful. Grooveson the shoulders help clean off some of the loose dirt to get atmoisture beneath it. Siping the shoulders is recommended if you arerolling the tire under when running lower tire pressures on a slicksurface. The sipes can help prevent the shoulder area of the tire fromglazing over and losing traction.
* Groove Widths: On some tracks, you can groove the tires twiceas much with a narrow groove, or half as much with a wide groove, andaccomplish the same thing. It depends on the track surface and howabrasive it is, or if it contains rocks that will tear up the tire. Youdon't want a lot of grooves on a rocky or highly abrasive track. Widergrooves stand up to these harsher conditions better.
* Groove Shapes: There are three basic shapes used in grooving:square, V, and sipes. Square grooves are the same width through itsentire depth. V grooves start out wide at the top and taper to nothingat their bottom. Sipes are thin slits cut by installing the blade upsidedown in the holder and using the separate ends of the blade to cutslices in the tire.
* Groove Angles: The angle at which grooves are cut determineshow much of the edges are exposed to the track when the car is invarious degrees of slide. The more the car will be sideways, the moreangle should be put into the grooves. As a dirt car travels around thetrack on a given line, the body is actually pointed toward the infieldin varying degrees. If the driver is consistent, you can determine anangle for the tire grooves that will work best for your combination.
* Grooves and Heat: Some tracks naturally put a lot of heat intoa tire and can actually cause the tire to melt or blister. On thesekinds of tracks, grooving helps cool the tire. The grooves (and sipes)help move air across the tire's surface, which keeps the treadtemperatures down. Grooving also produces more surface area, which helpstransfer heat out of the tire to the air. To help a tire dissipate heatwithout weakening the tread blocks too much, cut grooves in the centerof each block instead of cutting all the way across it.
8. CHEMICALLY ALTERED TIRES
While tire softeners are legal...
While tire softeners are legal at some tracks and many racers swear bythem, tire manufacturers strongly discourage this practice due to thepossibility of tire failures. It is up to you to weigh the risk versusreward of this practice.
Race Tires America strongly discourages this practice as a method forreducing lap times.
They advise against: (1) chemical alteration of the tread carcass and ortread compound, such as tire "soaking;" (2) use of tread softener; or(3) the physical defacement (removing, altering, or covering) oftire-sidewall markings in any manner. Failure to comply with thiswarning could result in premature or catastrophic tire failure that mayresult in serious injury or death.
Tire manufacturers are obviously sensitive to the liability of thispractice, but certain products on the market claim to help you reduce afew tenths off your lap times by softening the compound of your tire.Some tracks and sanctions have outlawed "soaking," while others stillallow it or turn a blind eye. While the practice of soaking tires iscommon, you should evaluate the level of risk you're willing to endureto possibly pick up a few tenths versus the chance of an untimely tirefailure.