May - June 2001 Motor State Performnace Report Article By Jim Kaekel, Jr.
For the most part, drag slicks are taken for granted, or at least they are until they fail to perform when a lot is expected of them. Weekend after weekend slicks are expected to consistently launch a car, and provide stunning launches and outstanding elapsed times. Unfortunately, during the rest of the week they are most likely exposed to nature's elements which can have adverse and long lasting effects.
Drag slicks are a major purchase, and a good deal of time and thought should go into their selection before pulling out the checkbook (or credit card). The correct size and sidewall configuration for a particular application, the best rubber compound, the proper rims for mounting the slicks, proper inflation, and even the racer's driving habits all play important roles in assuring that the slicks will provide maximum traction and long service life. Getting the most out of a set of slicks also involves important guidelines for maintenance and storage that must be followed.
Unless class rules dictate differently, select a big enough tire to let the car "hook" while still clearing all sheet metal and suspension components and allowing for tire growth at top speeds. Keep in mind that, with the exception of radials, slicks grow an average of 1" to 1-1/2" in diameter as the car accelerates, according to the experts at Mickey Thompson. The tire selected should have a diameter that yields the ideal engine speed in the "traps".
Sidewall choices range from soft, "wrinklewalls" to those that are relatively stiff. Stiff sidewalls distort less when "hit" (the precise moment the tires plant) and are recommended for use on cars that weigh in excess of 3,000 lbs, those equipped with four-links, and rear engine dragsters with "soft ride" rear suspensions. Generally, stiffer sidewalls will provide quicker reaction times because distortion in wrinkle type sidewalls can use up precious hundredths of a second before the car actually moves. Radial slicks, popular with drivers in NHRA/IHRA Stock Eliminator, offer another choice, but come with a heftier price tag. Most stock eliminator racers report that radials are at least a tenth quicker in the 1/4 mile than bias ply tires because rolling resistance is significantly reduced.
Rubber compounds must also be carefully considered because the same size slick may be offered in several different compounds. Medium and Medium/Soft compound tires work well on the majority of doorslammers while soft compound slicks are generally used on dragsters and altereds, lightweight, bodied race cars and drag cars that do not have rear suspensions. Obviously, if the correct size is chosen, but in the wrong compound, life of the slick and continued performance are going to be greatly affected.
When it's time to select rims for mounting the slicks, the width of the wheel should be within 1" of the tread width of the slick being mounted. For example, a slick with 9" of tread width may be safely mounted on an 8", 9" or 10" wheel. Mounting a narrow slick on too wide a wheel or, mounting a wide slick on too narrow a wheel will result in poor traction and uneven wear.
Inflation pressure depends upon the weight of the drag car and the diameter of the slick. As a general rule, cars weighing less than 3,000 pounds and using slicks in excess of 30" in diameter should run a minimum of 4-6 PSI. Heavier cars will usually require a minimum of 10 PSI.
Believe it or not, a racer's driving habits have as much to do with the life expectancy of the slicks as any other consideration. A racer who spends too much time in the water box is sure to generate a good deal of premature wear, and wind up with a lighter wallet to boot. According to Faron Lubbers of Hoosier Tire Company, "The tire's compound, soft or hard, shouldn't be confused with its longevity...the car's weight, horsepower and torque coupled with the driver's water box habits are the true determiners of longevity." On the majority of race cars, hard burn-outs are only necessary for the first few passes on a new set of slicks. Afterward, a light burn-out to clean any debris off of the tires and create a light, smokey haze is sufficient. "Dry hops" are unnecessary. Tires may be swapped, side-to-side, every 25-30 passes if "furring" or shredding appears on the tread area. Slicks on a car that launches hard may need to be rotated more often, according to Lubbers. (Carefully check sidewall information on the slicks before rotating to see if there are directional arrows indicated.) It's also a good idea to have tire covers handy on bright, sunny days, as the sun's ultraviolet rays are very harmful to drag tires.
Air pressure depends upon the weight of the car in question, and the diameter of the tire. Cars weighing less than 3,000 lbs. and running a tire in excess of 30", should operate at a 4-6 PSI minimum. Cars in excess in 3,000 lbs. should generally run a minimum of 10 PSI. Always be aware of the accuracy of the tire gauge. Check it with a friend's gauge, as more than one racer has been sidelined by something as simple and avoidable as an inaccurate tire gauge.
Off-season storage is definitely a key element in promoting long life expectancy for drag slicks. One racer may leave his slicks in an unheated garage all winter long, while another, more enlightened one may carefully wrap his in plastic bags and store them inside his home. Exposure to any of a number of destructive elements, including ultraviolet rays, ozone, extreme heat or freezing temperatures can wreak havoc with a tire's construction.
It is strongly recommended that slicks be removed from the car, deflated until only 5 PSI of air remains, placed in dark colored plastic bags and stored in a cool, dry place away from air compressors, electric motors and furnaces, which emit ozone which poses a real threat to slick longevity. Remember that slicks are not like typical passenger car tires, which are manufactured to withstand these elements. Drag tires are manufactured with one thought in mind: providing maximum traction to make drag cars launch harder and go faster and quicker. Follow these guidelines and get the most out of that "slick" investment.