You've just put the finishing touches on your new hi-po mill and dropped it in your street machine. It sounds great and runs strong, but every time you mash the throttle, all that increased torque blows the tires away and sends your rod sideways. You've come to realize that it's no faster out of the hole than when it had that old two-barrel lump under hood. The problem is a lack of traction. What to do? You could opt for a set of slicks, go the drag radial route, or walk the middle ground with a D.O.T.-legal slick. Here are a few pointers about picking tires, how to take care of them, and also a simple method for making sure they stick to the rims.
As indicated by their name, drag radials have a radial carcass designed to maximize off-the-line traction by using a soft compound and a reduced tread depth. Unlike slicks, drag radials maintain a stiff sidewall that ensures stability at high speeds, making them the most streetable of the three types of drag tires. While offering superior traction compared to ordinary radials, we'll focus on slicks as they require a different approach to care and feeding.
There are several D.O.T.-legal slicks available and they all share some common features—a soft compound and a two-ply wrinkle-wall construction, just like their cousin the drag slick. These tires are virtually slicks, but with grooves so they are legal for street use. (That doesn't mean, however, that they are suitable on rain-slicked streets.)
Drag slicks are racing tires which offer uncompromised traction. As the name implies, slicks have no tread so as to maximize the contact of the tire. Like the D.O.T.-legal slicks, drag slicks feature a soft compound and a soft, two-ply sidewall designed to wrinkle on launch. These tires should never be used on the street. If you were to get caught in the rain or drive through a puddle, they would instantly hydroplane. Also, due to their soft construction, slicks are prone to punctures, and handling is compromised.
Are Tubes Necessary?
Hoosier Racing Tires recommends that when its ''Quick Time'' DOT tires are used on the street, they should have an inner tube because race tires are inherently susceptible to air leakage. That's because they're constructed of a very light-gauge material needed to perform in various racing applications. In contrast, a radial tire's stiff wall construction lends itself to an excellent mechanical seal against the rim. A slick's soft sidewall is at a disadvantage in this regard. So, if your car spends any time on the street with DOT slicks and you don't want to refill them every few days, then by all means run an inner tube. Also, a tube will stiffen the sidewall of your slick, and possibly enable it to respond more quickly off the line by providing a more effective coupling between the rim and pavement. When having your slicks mounted, soapy water can be used to lubricate, but wax should be avoided as it may cause the tire to slip more easily on the rim (see sidebar below on how to screw tires to the rim).
Studying Your Footprints
How does tire pressure affect traction? Proper inflation is one of the single most important factors in the performance of a drag slick (this includes slicks of the DOT-legal variety). Traction can be dialed-in by adjusting tire pressure up or down. In order to determine how much pressure your particular tires require you must find a clean piece of pavement, preferably off the highway. Next, make sure that both rear tires have identical air pressure. Then, do a short burnout and examine the marks. As the pictures indicate, an over-inflated tire will leave a mark that is dark in the center, but light on the edges. This is known as ''crowning.'' An under-inflated tire on the other hand will show dark edges and a light center indicating that the tire is cupping. This procedure can also be used on radial tires. The final picture of this series shows what the proper pressure looks like: an even contact patch the entire width of the slick.
That's not all there is to it, though. Small incremental changes in tire pressure can have a meaningful affect on traction. Mickey Thompson Tires recommends adjusting your tire pressure up or down in half pound increments to precisely tune your slicks to the race track's conditions. Tire pressure will affect your reaction time. Keep in mind that an underinflated tire reacts more slowly than one with more air pressure.
So, you keep reducing the pressure in your tires and your 60-foot time (also known as your short time) keeps dropping. All well and good, but you also begin noticing that the car is no longer stable on the other end of the track. Reducing air pressure in your slicks often improves traction, but often the tradeoff is reduced stabilty. They say you haven't lived until you've done the ''slick dance'' through the lights at a buck-fifteen-plus. Remember, eight pounds of tire pressure is great at the starting line, but those same eight pounds are holding up the back end of the car while you are hurtling down the track. Be sensible with tire pressure. It's better to give up a couple of hundredths of a second on your 60-foot time to avoid a catastrophe on the big end.
How do you get a handle on air pressure? Don't expect to use an ordinary auto parts store tire gauge; you know, the type that fits in your pocket like a pen. The instrument used to measure tire pressure in a drag slick needs to be capable of reading accurately at low pressures. Any mail-order parts house offers a variety of good tire gauges for this purpose. Expect to pay between $20.00 and $250.00—it's a worthwhile investment.
Hazing the Hides
Now imagine yourself in the staging lanes at the local dragstrip, new slicks mounted on the back, waiting for a turn in the water box. A million things are going through your head: Do I roll through the water? Do I do my burnout in the water? How long of a burnout should I do?
Every slick manufacturer recommends a different burnout procedure with their tires, and most racers have their own techniques as well. The manufacturer's suggestions should be followed, but ultimately, the method you use is better determined through testing and tuning of a particular combination. After their burnout, some racers perform dry-hops—barking the tires without the aid of water. Others prefer to immediately stage after smoking the hides. The burnout accomplishes two important tasks: 1) It cleans the surface of the slick allowing it to perform to its capacity; and 2) It heats the tire, softening the rubber, enabling it provide traction.
Mickey Thompson recommends that the first burnout of the day be a hard one while subsequent burnouts should be light. Some slicks require a minimal burnout to clean and soften the rubber. Racers sometimes employ traction enhancing chemicals on the starting line surface. These traction compounds, such as VHT, greatly enhance the traction capabilities of a slick-type tire. It is used on the starting line for racers to do their burnouts providing a surface that works like glue. VHT allows for an even more aggressive launch.
Handle With Care
Unlike street tires, slicks require special handling. Under no circumstances should slicks be stored outdoors, because this will accelerate dry rot. A slick with cracked sidewalls is unsafe and should be discarded. If stored off of a vehicle, slicks should be sealed in opaque plastic bags and kept out of direct light, either sunlight or fluorescent, also extremes in temperature. If stored on a vehicle, weight should be taken off of them by elevating the rear of the car with jack stands (never use a jack for this purpose!). The weight of a vehicle can eventually distort a pair of slicks. These tires should be treated with the utmost respect as they play a crucial role in your car's performance and your safety.
