Street Car Slicks - Your Cheating Heart

Street Legal Slicks

Wayne Scraba Jun 1, 2000 0 Comment(s)
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It looks like a slick. It feels like a slick. It hooks like a slick.It must be a slick. We have news for you. It's not. It's a "ET Street" tire from the folks at Mickey Thompson. Basically, this is a specialized tire designed solely for the burgeoning Quickest Street Car marketplace. While these tires might look like slicks, there are a number of differences between the two types. Some of the differences are subtle. Some aren't.

When '55-56-57 Chevys were almost new, the hot tire setup for a fast car was a set of recapped Atlas Bucrons. Eventually tire technology evolved to the point where dedicated drag slicks were readily available. Decades after recap slicks made their debut, everything came full circle: Street tires with a tread pattern that offered the hook of a slick were developed. And with that came classes of competition where "street" tires with a tread pattern were required. The cheater slick was born. The cycle continued, and good old-fashioned slicks became the norm for almost all serious drag race applications. But then Quickest Street Car drag racing blossomed (thanks in no small part to Super Chevy Shows). Sticky street tire compounds were released. The tire wars heated up and before we knew it, tire technology had come full circle. And no, recaps aren't the hot ticket. Instead, we're blessed with what could be the most capable "cheater slicks" ever developed.

Why the fuss? That's easy. The rules for many categories of street car drag racing mandate a tire that has Department of Transportation (DOT) approval. In these categories, if you show up with slicks, you can't play. But the DOT requirement also places a heavy burden on the tire manufacturer. The company has to develop a tire that can effectively cope with an almost obscene amount of horsepower, but at the same time, it must pass a rigid set of requirements laid out by the DOT.

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It doesn't take a rocket scientist to see that the M/T ET Street tire has a tread pattern. Yes, it has grooves because many of the street car racing organizations mandate them. But the grooves are part of a package that is most definitely a tight rope act. As an example, M/T engineers tested a number of different groove configurations. While the actual grooving configuration and method used to develop it are proprietary, Mickey Thompson found that the groove shown here showed the best performance and overall reliability during testing. Because of this, it made the grade for the production tire.

Given the rules concoction, the "street" tires used in street car drag racing might look exactly like slicks with a couple of grooves cut in them, but they have a number of subtle and perhaps not-so-subtle differences. One factor is weight. Two issues have an influence on the overall mass of a fastest street car tire, and they're both important. The first thing one has to keep in mind is the fact a typical fastest street car is quite often heavier than it's true drag race counterpart, even if the tire sizes are identical. It's not uncommon for an "Outlaw" Pro Street racer to tip the scales at a figure that's very close to 3,000 pounds, or more. That same car can have an ultimate performance that's on par with a current NHRA Pro Stock car, but the Pro car weighs 2,350 pounds.

There's more to this weight equation: Now, it's no secret that drag slicks for unlimited applications are often constructed to be as light as possible. That just isn't the case with a tire that is forced to pass a DOT requirement. A DOT tire must have a load range (and it must have that load range cast into the side of the tire). Using the Mickey Thompson 33 x 18.5-15LT shown in the accompanying photos as an example, the overall tire weight is 43 pounds. A similarly sized conventional M/T ET Drag slick tips the scales at 37 pounds. Where does the weight come from? Mickey Thompson points out that more belt material was required in the ET Street race tire. This made for a more rigid sidewall and of course, a heavier tire. In simple terms, the manufacturer is forced to build a more robust tire if it has to conform to heavier cars and DOT requirements. M&H Tire perhaps sums it up the best: "The manufacturer must offer the right product for the weight of the vehicle. That's the manufacturer's job."

Compounding is another point that must be addressed by the manufacturer. There are a couple of different avenues taken by companies who have entered the street car drag racing arena. For example, Hoosier compounds their Quick Time Pro street tires differently than their drag tires. M&H Racemaster has developed an entire new line of compounds just for their newest "HB" series of street car drag race tires. On the other hand, Mickey Thompson uses compounds that are identical to their most popular drag slick compound (M5). Mickey Thompson supplied a compound chart to show how their ET Drag slicks and ET Street tires compare which can be found on the last page of this article.

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When you take the time to peruse the specs for street car race tires and compare them to an identically-sized slick, you'll often find that many of the street tires are heavier. Why? Two reasons: DOT tire requirements and the weight of the car.

The type of burnout you perform is related to the tire compound. For a car equipped with M5 compound tires, M/T offers this advice: "For the first pass of the day, make a hard burnout. Once that is accomplished, for an automatic transmission car, make a fairly hard burnout on the first pass or two. After that, a light burnout should suffice. For a stick shift car similar to a Super Stocker (a relatively heavy, full-bodied car), perform a light burnout, haze the tires, and stage immediately. Generally speaking, tires work better with a light burnout rather than a hard burnout. ET Street tires may require a fairly hard burnout on the first and second pass to break them in."

When it comes to overall life expectancy, these new-generation Quickest Street Car tires are much the same as slicks, and slick life can vary from car to car. According to the experts, inconsistent 60-foot and 330-foot times are caused by tread wear or carcass breakdown. These should be signals that it's time to change tires. While slicks have wear indicators on the tread face, street car tires don't. Typically when the grooves in a street car drag race tire are gone, then it's time to buy new rubber (the various sanctioning body rules might also stipulate that some tread must remain). Remember, cars that launch hard can cause the tire carcass material to break down. A good rule of thumb is to inspect your tires carefully after 30 passes. And if the car is very quick, the tires should be inspected more frequently.

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In order to meet the specialized requirements, street car race tires most often require more belt material. This tends to stiffen the sidewall and it also adds weight to the tire. This particular tire, a M/T 33X18.50-15LT, weighs approximately 6 pounds more than a similarly sized M/T slick.

Street car "slicks" are typically designed as tube-type tires. There are a number of reasons for this, but safety is a primary concern. In addition, a tube helps to maintain air pressure. It's not uncommon for a tubeless fastest street car tire to deflate quickly (that even includes several of the more streetable types with a full complement of tread). Mickey Thompson states that tubes will enhance the reaction time, increase the stiffness of the tire, and reduce sidewall shock and deflection when launching the car. Finally, the manufacturers polled claim that a tube helps with consistency, since the tube actually absorbs some of the heat from the tire.

What is the right type of tube to use? In drag racing, a natural-rubber tube is the most common. Although it sometimes done, it's not a good idea to use tubes designed for large trucks, since they are not sized correctly. For the most part, each manufacturer of drag race street tires will have an appropriate tube size for a given tire. What if you don't use the correct tube? Figure on replacing them often. One of the biggest causes of tube failure is the use of an incorrectly-sized tube.

According to Mickey Thompson, you may notice a low spot or wrinkle in a tube-type tire. This is often caused by the wrong tube size (the tube is either too large or too small). It can also be caused by a faulty installation. In order to confirm this, break the tire down and rotate it on the rim. You'll note that the low spot (if it is still there) has not moved. If you break the tire down and replace the tube with a standard tubeless style valve stem, then the low spot or wrinkle is eliminated. This should tell you that the tube is the root of the low spot. In order to eliminate wrinkles, the tube must be inflated and deflated during installation. If the wrinkle persists, you may have to lubricate the tube with talcum (baby) powder and/or break the tire down and work the wrinkles out by hand.

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The sidewall of a DOT tire includes some important information. For example, this M/T tire shows the load range, the maximum tire load (2,170 pounds) and the sidewall and tread construction (2-ply and 4-ply, respectively). One thing you won't find on a M/T tire is a directional arrow. It's not required since the tires can operate in either direction.

What range of tires are available? You might be surprised at the choices. Using Hoosier and Mickey Thompson as the examples, sizes range from 8-inch wide by 26-inch tall tires all the way up to simply massive 22-1/2-inch-wide by 35- inch tall tires (these huge by large tires have true tread widths of 17 inches)! Mickey Thompson has 14 tires in their ET Street series, while Hoosier offers 17 different tires in their Quick Time Pro series. Mickey Thompson sizes are in the 15 and 16-inch rim diameter range, while Hoosier's line up covers sizes in 14, 15, and 16-inch rim diameter sizes. In terms of rim width, each manufacturer publishes a range of wheel rim widths that are applicable to the tire you select. This is most often referred to as the "design rim" in the application charts. Typically, street drag tires are available in sizes to fit rim widths ranging from 6 inches all the way up to 16-plus inches.

On another front, M&H Racemaster is in the process of releasing an entire new line of DOT race tires. In the past, the M&H tires were primarily a full-tread design. The new lineup (called the HB-10 series) is based upon the in-vogue "cheater slick" configuration. In other words, shallow grooves and maximum dry weather race track traction. What's interesting about the M&H lineup is the fact they have taken a focused approach to sizing. Many of the rules currently in style for Quickest Street Car drag racing limit certain classes to a "10-inch wide" tire. For practical purposes, these tires are most often 11.5 inches wide (the maximum most sanctioning bodies will accept). None of the rules limit diameter, and as a result, M&H will offer at least three different tires to fit this rule: An 11.5 X 30-inch tire, an 11.5 X 31-inch tire, and a monstrous 11.5 X 32-inch tire (shades of vintage Top Fuel tires). Other sizes will be offered as well. Expect to see these tires available for sale as this is printed.

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Another thing to keep in mind is the DOT marking. For some racing organizations, this is mandatory if you're going to compete. There are a number of classes that restrict cars to DOT tires only. Some specify maximum tire dimensions. Others don't.

How much air pressure is required for these tires? According to Mickey Thompson, proper air pressure is critical in their ET Street drag tire, especially from a performance perspective. Thompson notes that recommending air pressure isn't easy, since there are so many variables involved. For example, the weight distribution of the car, the transmission type, the chassis setup, wheel size, and other factors add up, and they can have an effect upon operating pressures. M/T offers this advice: "In drag racing, many racers feel that "less is better" with regard to air pressure. This is not always the case. While there are exceptions to every rule, we have found higher pressures generally work best with Mickey Thompson tires. Not only do the higher pressures lead to quicker times, but they also contribute to a safer, more stable ride at the finish line".

Mickey Thompson has a list of six categories as recommended starting points for tire pressure. According to M/T, the actual optimum air pressure may vary significantly, depending, of course on the previously mentioned variables. The recommended baseline pressures are on the last page of this article.

Summary
As you can see, tires designed principally for street car drag racing are not slicks with a couple of grooves cut in them. But they are dedicated race tires that were designed from the ground up for the application. Given the reduced tread depth and the special compounds found in these tires, they should be used on dry pavement only and they really aren't suitable for highway use. Remember, these are specialized race tires. And they offer way more bite than a set of recapped Atlas Bucrons!

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Specialized tires manufactured for street car drag racing aren't restricted to a few sizes. All of the major tire manufacturers who offer tires for this marketplace have a full compliment of sizes available. When shopping for tires, it's best not to place much stock in the actual printed sizes. Just like slicks, you need to check dimensional charts. The 33X18.50-15LT tire shown in the photo is positively huge, and it's not the biggest tire available either! See the next photo:

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The vast majority of DOT race tires are engineered to operate with tubes. The tube of choice is a natural-rubber race car tube such as this. Advantages of running tubes in tires such as this are manifold: Tubes tend to absorb some of the tire heat. They allow for better consistency. They're safer. You'll also find that tubes save a bunch of flat tire aggravation as well. Even fully treaded, sticky street tires tend to lose air pressure. Obviously, this dilemma isn't as common when tubes are used in the mix.

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Mickey Thompson points out that some wheels will not accept a tube valve stem. The valve stem hole in the rim must measure 5/8-inch. If it becomes necessary to drill the hole to a larger diameter, make sure the new hole in the rim is deburred and free of sharp material. Before installing new tubes, pre-inflate them to the approximate diameter of the tire. This will aid in filling the entire cavity of the tire by stretching the tube. Mickey Thompson notes that this will also aid in valve stem placement on wide rims where the valve stem is offset on the rim, but not offset on the tube.

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The tape measure supplies a measure of scale for the tire. As you can see, it's no welterweight. Manufacturers who offer dedicated drag race street tires can supply upwards of a dozen sizes for various car combinations. And don't scoff at the performances either. Some of the competitors have run in the 6.80 to high 6.90 range at speeds approaching 205 mph with this rubber.

Sources

M&H Tire Company
Gardner, MA 01440
Hoosier Racing Tire Corp
Lakeville, IN 46536
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