Slick
A slick is a treadless tire , which, at the right temperature, is suitable for use on dry or slightly damp roads due to its very adhesive tread compound.
Slicks in motor vehicle racing
In contrast to slicks, there are rain tires and intermediates that have a profile. While slightly profiled intermediates have the same rubber compound as slicks in order to still work on dry roads, rain tires have a strong profile and an even softer rubber compound.
An important parameter is the temperature . This must be in a suitable range at approx. 80 ° C - and thus higher than for normal car tires. A racing tire has little grip below this. It is important to have the correct air pressure and the chassis geometry , often with a negative camber , in order to increase the contact area (the proportion of the tire tread that is in contact with the asphalt) when cornering. Since slicks heat up considerably more than conventional tires, they have to be approached with a much lower cold air pressure (often only 1.5 to 1.8 bar ). The air pressure then rises by around 0.7 to 1 bar at operating temperature and is usually still lower than with road tires. In this way, however, a larger contact area is achieved. Ideally, the measured temperature should be identical over the entire width of the tires when they are hot; a sign of the even load on road contact. The temperature measurement is therefore always measured at three points, distributed over the width of the tire.
At several points on the tread there are small holes for measuring wear, which can be done with the help of a tread depth gauge, as is known from road tires. The holes are evenly distributed over the circumference of the tire and are located both in the middle and on the right and left near the edges of the tread, in order to be able to determine uneven wear on the inner and outer sides.
A higher mileage of slicks is achieved through so-called heat cycling . The tires are briefly brought to operating temperature by machine or by one or two run-in laps and then stored for at least 24 hours. Chemical processes in the rubber compound then make it more stable; without any loss of adhesion.
Slicks on motorcycles
The description under "Motor vehicle racing" also applies here. In motorcycle racing, however, there is also a change in cross-section. While the cross section of a road tire is more like a U, slicks have more of a V cross section. This leads to significantly more stable driving behavior in an inclined position. However, the stable straight-ahead driving at low speeds suffers considerably.
Slicks on bicycles
There are various jacket manufacturers who have slick tires on offer. Schwalbe, Continental and Michelin should be mentioned. They are mainly used in cycling , but are also becoming more and more popular on city bikes, because they offer the best grip when driving on the asphalt and, thanks to their lower rolling resistance, enable faster and less forceful driving.
Slicks on drag stars
In " drag racing " (a type of motor sport that is all about maximum acceleration) the demands, especially on the rear wheels, are enormous. The races are held on tracks specially prepared with rubber and glue for optimal grip . The slicks used in drag racing for this purpose are specially designed for these needs. At the moment (as of 2020) only one make of tire is permitted in the top class, the so-called Top Fuel category: The " Goodyear Eagle Dragway Special" This tire is certified up to 563 km / h.
The rear tires are huge at 36.0 × 17.5–16 and have a circumference of around 3 meters. The tires are filled with a very low pressure of just 0.6 bar. They are designed so that they change in diameter and width with increasing speed. The static diameter of about 92 cm increases to 150 cm, while the width shrinks from 46 cm to about 26 cm. This effect leads to a “variable transmission ratio” in terms of speed (distance covered per tire revolution). The sidewalls of the tires are designed in such a way that they “fold” as it were when you accelerate, as the rim of the wheel rotates faster than the tire and the sidewalls during initial acceleration. The resulting twist is called "wrapping". When the tire is wrapped to the maximum, the contact with the track is as long as possible and offers maximum traction. This phenomenon can be seen well in numerous super slow motion videos. As soon as the TF has left the start line, the tires quickly become higher and thus narrower, which leads to less contact with the track surface. At the beginning of this process there may be a so-called “tire shake”. The reason for this is that the tire does not detach itself from the twist, but rather “rolls over” itself in this state, shaking the car violently. US professional teams use a rear tire for 4 to 5 runs (about 2 kilometers). A series production car tire for the EU market has a mileage of around 25,000 to 50,000 km. A TF rear slick costs around US $ 500–600.
The front tires are 3 inches (7.6 cm) in diameter and mounted on 17 inch (43 cm) wheels. Tire pressures vary between 70 and 100 psi (4.8 to 6.8 bar). At takeoff, unlike the rear tires, they have a "quiet job" as they are often in the air for 60 feet or more. These tires are also certified up to 560 km / h and are typically used for around 20 runs or around 5 miles.
The tires are made from a very heat-resistant and hard-wearing rubber compound called "D2A". At the center of the tire, this mixture is about 0.20 inches (5.08 mm) thick. That is less than 1% of the total tire structure. The load-bearing structure is a fabric carcass, which consists mainly of nylon and ensures the required flexibility and deformability of the tire. Tire wear is measured through small holes in the rubber, which the team can use to estimate how thick the tread is and when a change is required.
Although “ tire warmers ” would be available for TF dragsters, burn-out has become the main method for increasing the temperature of rear slicks. The dragster drives through a small amount of water and then lets the tires spin, causing them to smoke. During this process, the temperature rises up to 120 ° C. The “high art” in the following is to keep the heat in the tire until the actual start by the driver with the help of his guide steer the car back in the own “hot” rubber tracks that he has just laid, and additional heat ( and traction) by scrubbing old "rubber compound" off of his tires and adding fresh rubber to the track for extra grip. After a run, the tire temperature can briefly be 160 ° C to 180 ° C, not because of the frictional heat during burn-out , but primarily because of the enormous flexing work (mechanical stress / deformation) of the tire.
history
The use of slicks has its origins in the US motorsport scene in the 1950s and 1960s. Back then, tires for acceleration races were “shaved”, that is, the tread depth was reduced. Products from Dunlop and the Goodyear Blue Streak were particularly popular . From 1971 to 1997 , specially produced slicks were used in Formula 1 , with which the lap times achieved up to then could be greatly improved. This is why the faster, treadless tires also established themselves in touring car and motorcycle racing in the 1970s. In 1998 they were banned again in Formula 1 in order to reduce the maximum cornering speeds for safety reasons. Instead, so-called "grooved tires" were prescribed (initially with three longitudinal grooves at the front, four at the rear, and four grooves at the front and rear from 1999 ). In the years that followed, however, it became clear that these tires became more and more efficient and thus hardly brought any safety gains. Since the 2009 season , slicks have been allowed again in Formula 1.
Strengthen
With slicks, a larger contact area is achieved between the road and the tires. This results in a higher adhesion limit ( Grip ), so that with the additional interlocking effect a greater driving force ( traction ) and can be transferred particularly cornering force. In addition, a profile would impair the tire's smooth running on asphalt and the power transmission due to additional rubber deformation or flexing. By not having a negative profile, a tire has more rubber and thus more wear reserves. It can still function well under high loads and at temperatures of over 100 ° C. The development of noise is reduced by the fact that no profiling is used, and tire squeal hardly occurs.
For these reasons, lap times on dry racetracks are greatly improved by using slicks. According to driving tests carried out by the magazine sport auto with series sports cars on the old, short version of the Hockenheimring (without the new chicane at the end of the crossbar), the time saved compared to street-legal series tires is around four seconds, compared to street-legal sports tires it is still around 2 seconds; based on a lap time of approx. 1:14 minutes with slicks.
weaknesses
Slick tires can be used in dry and slightly damp racing conditions. The main problem on wet roads is the drop in temperature below the optimal range, which means that the adhesion decreases considerably depending on the rubber compound used. If there is moisture on the asphalt, a film of water forms between the tires and the road, resulting in aquaplaning , in which the vehicle can no longer be steered.
The boundary between grip and loss of grip is narrower with slicks than with treaded tires; a breakaway of the vehicle thus happens at a higher speed, but much faster. Since the maximum traction when accelerating and braking and the cornering force (in curves) are only achieved with a slip of around seven to ten percent, exploiting the possibilities of slicks requires considerable skills and experience.
The rubber compounds used in slicks and the stress on racetracks limit the service life of tires to a fraction of that of road tires. After less than 200 kilometers, the tread can be worn down to the carcass .
The large contact area and the lack of a negative profile allow slicks to react very sensitively to bumps in the road and ruts . The straight-line stability can be severely impaired, so that constant steering corrections may be necessary.
As a rule, slicks are only sold by the tire manufacturers' racing tire departments and only to holders of racing licenses .
Hints
- The area independence of the friction only applies to rigid bodies, which do not include motor vehicle tires.
- This type of tire is forbidden for motor vehicles on public roads due to the regulation with at least 17% negative profile.
- This type of tire has no advantages for motor vehicles on public roads because the operating temperature cannot be reached there.
See also
Web links
- Achim Kuschefski: Grip. (PDF; 738 KB) Institute for Bicycle Safety e. V., August 2010, accessed on January 14, 2019 .
- Markus Fach: Local effects of friction between car tires and road surface. (PDF; 4.55 MB) Technische Universität Darmstadt, April 1999, accessed on January 14, 2019 . Fach_FZD_Dissertation_1.pdf
- Topfuel dragster race slow motion Very good to see, the so-called "tire distortion". On YouTube . Retrieved July 16, 2020
- We Break down the Physics of Dragster Tires . Article about dragster tires. Retrieved on July 16, 2020 (en)
literature
- Michael Trzesniowski: racing car technology . 2nd Edition. Vieweg and Teubner, Wiesbaden 2010, ISBN 978-3-8348-0857-8 .
Individual evidence
- ↑ Michael Trzesniowski: racing car technology. 4th edition. Vieweg and Teubner Verlag, Wiesbaden 2014, ISBN 978-3-658-04918-8 . P. 237
- ↑ a b c Dan Welberry: Top Fuel Dragster / Owner's Workshop Manual . Ed .: Haynes Publishing. Haynes Publishing, Somerset, UK 2014, ISBN 978-0-85733-265-3 , pp. 44-46 .
- ↑ a b c Hockenheim-Ring GmbH: Motodrom Insight / The official Hockenheimring magazine . Ed .: Hockenheim-Ring GmbH. Edition 2020. Hockenheim 2020, p. 23 .