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A racing slick (also known as a "slick tire") is a type of tire that has a smooth tread  used mostly in auto racing. The first production "slick tire" was developed by M&H Tires in the early 1950s for use in drag racing. By eliminating any grooves cut into the tread, such tires provide the largest possible contact patch to the road, and maximize traction for any given tire dimension. Slick tires are used on road or oval track racing, where steering and braking require maximum traction from each wheel, but are typically used on only the driven (powered) wheels in drag racing, where the only concern is maximum traction to put power to the ground.
Slick tires are not suitable for use on common road vehicles, which must be able to operate in all weather conditions. They are used in auto racing where competitors can choose different tires based on the weather conditions and can often change tires during a race. Slick tires provide far more traction than grooved tires on dry roads, due to their greater contact area but typically have far less traction than grooved tires under wet conditions. Wet roads severely diminish the traction because of aquaplaning due to water trapped between the tire contact area and the road surface. Grooved tires are designed to remove water from the contact area through the grooves, thereby maintaining traction even in wet conditions.
Since there is no tread pattern, slick tire tread does not deform much under load. The reduced deformation allows the tire to be constructed of softer compounds without excessive overheating and blistering. The softer rubber gives greater adhesion to the road surface, but it also has a lower treadwear rating; i.e. it wears out much more quickly than the harder rubber tires used for driving on the streets. It is not uncommon for drivers in some auto sports to wear out multiple sets of tires during a single day's driving.
In Formula One, slick tires were not used from the 1998 to 2008 seasons. Dry weather tires with mandatory circumferential grooves intended to reduce total grip and reduce cornering speeds were used, and were still often referred to as "slicks" as the grooves were not intended to disperse water and could not be used effectively in wet conditions. Slick tires were reintroduced from the 2009 season.
Drag racing slicks
The first drag racing slick was developed by a company called M&H Tires (Marvin & Harry Tires) in the early 1950s. It was the only company in the world that produced and sold original drag racing tires.
Drag racing slicks vary in size, from slicks used on motorcycles to very wide ones used on Top Fuel dragsters. For "closed wheel" cars, often the car must be modified merely to account for the size of the slick, raising the body on the rear springs for the height of narrower slicks, and/or replacing the rear wheel housings with very wide "tubs" and narrowing the rear axle to allow room for the wider varieties of tires. Open wheel dragsters are freed from any such constraint, and can go to enormous tire sizes (the opposite of tripodal which are quite minuscule). Some use very low pressures to maximize the tread contact area, producing the typical sidewall appearance which leads to their being termed "wrinklewall" slicks. Inner tubes are typically used, to ensure that the air does not suddenly leak catastrophically as the tire deforms under the stress of launching.
"Wrinklewall" slicks are now specifically designed for the special requirements of drag racing, being constructed in such a way as to allow the sidewall to be twisted by the torque applied at launch, softening the initial start and thus reducing the chances of breaking traction. As speed builds, the centrifugal force generated by the tire's rotation "unwraps" the sidewall, returning the energy to the car's acceleration. Additionally, it causes the tires to expand radially, increasing their diameter and effectively creating a taller gear ratio, allowing a higher top speed with the same transmission gearing.
Since completely slick tires are outlawed on most roads due to their inability to handle wet pavement, the "cheater slick" became a popular item in the hot rod world in the 1960s; a typical slick type tire, but engraved with the absolute minimal amount of tread grooves required to satisfy legal requirements. Since then, however, tire development has progressed greatly, so that today's hot rod street cars typically use wide, grooved tires which perform better than the slicks of the past; while the cheater slicks available today, both for nostalgic appearance of street cars and for competition use in classes where DOT approved street tires are required, have followed their own line of development, diverging from true slick tire construction to become a distinct tire design in themselves.
R compound tires (grooved slicks)
The development in cheater slick technology has affected the development of tires for racing series other than drag racing as well. When other forms of auto racing similarly instituted classes which require DOT approved street tires, some manufacturers similarly began to market tires which superficially resembled their high performance street tires, but with the least tread pattern permissible and with very soft, sticky rubber, intended specifically for competition because the soft tread would wear too quickly for street use. These became known, loosely, as R compound tires. With additional years of progress, this class of tire has in its turn followed its own line of development, to the point where they have little in common with true street tires of the same brand. Ironically, this has led to new classes of racing which require not only DOT approval, but also a minimum treadwear rating, in an effort to eliminate the R compound tires from competition and require "true" street tires.
In contrast, many bicycle tires made for street use are slick. Aquaplaning does not present a problem for bicycles due to their narrower width, higher pressure, lower speed, and circular cross section (due to the need to lean the bicycle in turns), the bicycle tire can penetrate the water layer to contact the road much more easily; in practice, grooved bicycle tires do not outperform slick tires on wet roads. However, many low and medium performance bicycle tires have substantial tread depth, because the bicycles are designed with off-road excursions in mind: in dirt, gravel, or sand the tread pattern provides significantly improved traction. In addition, high performance bicycle tires, although designed for road use only, often have a very fine tread pattern, which appears to provide no difference in performance versus a slick tire and is only there for marketing purposes and as a tire-wear indicator. This is clear not only from direct testing of tires, but also from the fact that the texture of the road is itself coarser than the minimal tread pattern on these tires. Some grooveless designs have small "holes" or dimples embedded in the tread as a tire-wear indicator. This is similar to automobile tire-wear indicator bars, which contact the road when the tire is worn to a low tread amount, making the tire noisy on the road.
- "V-STEEL SMOOTH TREAD-MS". Bridgestone. Retrieved 2012-01-31.
- "Why a Smooth Tread on Road Tires?". Michelin. Retrieved 2012-01-31.
- Jobst Brandt. "Tires with smooth tread". Retrieved 2012-01-31.
- Christopher Neiger. "Why doesn't NASCAR race in the rain?". HowStuffWorks. Retrieved 2012-01-31.
NASCAR tires have a completely smooth tread.
- Sheldon Brown's Tire Page