Design Considerations for a Racecar Tyre - Essay Example

5 Mar. 2008 design considerations for A RACECAR tyre Introduction Tyres form the last section of the transmission system wherein a part of the engine's output is used up to provide the motion of the automobile. Formula One tyres play a significant role in the performance a Formula One car. The tyres have undergone significant changes throughout the history of Formula One, with different manufacturers and specifications used in the sport. Formula One tyres bear only a superficial resemblance to a normal road tyre. Whereas the latter has a useful life of up to 80,000km, the tyres used in Formula One are built to last less than one race distance. This is determined by the compound of the rubber used. By regulation, the tyres feature a minimum of four grooves in them, with the intention of slowing the cars down. A slick tyre, with no indentations, is best in dry conditions. Both front and rear tyres are typically 660 mm in diameter. They can be no wider than 355 mm and 380 mm at the front and rear respectively. Slick tyres are rumoured to be reintroduced as of 2009 but the FIA regulations (though they can be changed) still have Formula One using "grooved" tyres in 2008. There are several factors affecting the performance of formula 1 cars' tyres that should be considered before designing it. These factors include the road conditions, temperature, humidity, contact area with the ground and a few others. In tyre design, there are three main considerations - the profile and size, the tread, and the compound. Let us see about the tyre technologies used and the problems faced in tyre designs for formula one cars. Developments in Formula One tyre technology Racing tires are highly specialized according to vehicle and race track conditions. Tyres are specially engineered for specific race tracks according to surface conditions, cornering loads, and track temperature. Tyres have also been specially engineered for drifting. Racing tyres are often engineered to minimum weight targets, so tires for a 500mile race may run only 300miles before a tyre change. In 2005, tyre changes were disallowed in Formula One, the compound was harder as the tyres had to last the full race distance (around 300km). Tyre changes were re-instated in 2006, following the dramatic and highly political 2005 United States Grand Prix. For the 2007 season Bridgestone is the sole tyre supplier and have introduced four compounds of tyre, two of which will be made available at each race. The harder tyre is more durable but gives lesser grip, and the softer tyre gives more grip but is less durable. Both compounds have to be used by teams in a race and the softer tyre has a painted white stripe in the second groove. Each team must use each specification during the race, unless wet or intermediate tyres are used during the race, in which case this rule no longer applies. In extremely wet weather, such as that seen in the 2007 European Grand Prix, the Formula One cars were unable to keep up to the Safety Car in deep standing water due to the risk of hydro planing. Rubbers used in tyres are generally styrene-butadiene co-polymers, natural rubber, or polybutadiene. These can be blended in whatever ratio is desired. The styrene content can be varied to give a hard wearing rubber, or a high styrene cling rubber to maximise wet grip at the expense of heat build up. Everything is a compromise aimed at giving the best performance for a particular application. For example, when a new circuit is laid down the surface is very abrasive, and polybutadiene has a superb abrasion resistance to sliding on sharp surfaces. However, it is hopeless in the wet, since grip suffers appallingly. In car racing of course, grip is everything. The second most important variable is the carbon black type that is used. As a general rule, the finer the carbon black, the higher the abrasion resistance, and the higher the heat build-up in the rubber compound in service. There is another variable, the "structure' of the carbon black, a measure of the agglomeration of the particles. Most tyre compounds will contain 25% to 35% carbon. It's the carbon that reinforces the rubber improves abrasion and tear resistance, tensile strength, and lots of other characteristics. The third variable is the "state of cure". In other words, you can make "hard rubbers" merely by making adjustments to the level of "curatives" - sulphur and accelerators added to the mix. Add all these variables together, and the usual range of tread rubber hardness can vary quite considerably. Hardness varies with the temperature of the rubber. This affects other properties as well. Formula 1 go even further by wrapping their tyres in the pits in electric blankets to warm them, so that the driver won't be caught out by an abrupt transition from race hot tyres, to cold newly fitted tyres, which don't grip as well. An interesting development in Formula 1 has been the compulsory adoption of grooved tread patterns. The tyres are grooved circumferentially, rather similarly to the patterns used on aircraft tyres. They have one purpose- to slow the cars down! There is less rubber on the road than a slick tyre. A high proportion of the drag generated by an Formula One car comes from the tyres. The downforce is controlled by the spoiler or wing on the rear of the car, plus other "aerodynamic aids" placed at critical points around the car, following wind tunnel testing, designed to hold the car on the ground. Tyres regulations have changed a lot in Formula One history in order to limit cornering and acceleration speeds of the cars. After all, the tyres are the only contact patch between a car and the ground. It needs no explanation that any change in tyre regulation can greatly influence the performance of a racecar. It is therefore very important for the FIA to study all possibilities if they decide to change any of these regulations. Changes of tyre width had proven to have the opposite effect than intended. A smaller tyre in fact reduces grip, but it also reduces aerodynamic drag, hence enabling higher straight speeds. It was also a considerable advantage that the corners could be taken sharper, as the total width of the car was reduced a little.. The use of tubeless tyres is yet another trend in Formula One technology which brings down the rate at which the tyre gets blown out during a puncture CHALLENGES FACED IN TYRE DESIGN FOR FORMULA ONE CARS The following are some of the challenges faced in the design of tyres. The tread grooves cannot be placed over the edges of the reinforcing belts in the casing, since they will quickly cause the tread to crack circumferentially, which will "throw the tread" causing a catastrophic failure. The rubber in tires, especially tread rubber, undergoes cyclic stress at very high levels. The work done by these rubbers result in heat generation. The combination of high cyclic stress and high temperature is bound to generate mechanical and chemical changes in the rubber (Haney). As the temperature of the tyre changes, so does the dynamic quality of the tyre. If it gets too hot, the amount of heat being generated cannot escape to the cooling air stream quickly enough, rubber being a very good insulator, the heat builds up at either the thickest part, or the part under most stress, for example the outside front tyre on a banked circuit, and the tyre "goes off' in race car speak. It loses some of its rubbery characteristics and will probably blow apart. The temperature at the thickest part of the tread is monitored by inserting a needle pyrometer, which gives a digital readout of the temperature at the point of the needle inside. The tyres have a dimple on the buttress to indicate where the needle should be inserted to a calibrated depth. Being race tyres, the tread is not very thick, so this has to be done carefully, and quickly. Some other challenges have led to a research in developing a tyre for all seasons. They are: reduced costs for manufacturers; reduced development time required for teams; reduced running speeds in dry conditions; much reduced running speeds in wet conditions; The tyres would obviously have to be a compromise between wet and dry ideals. Currently, cars running in dry conditions use relatively hard rubber, which operates at an ideal temperature in the region of 80 degrees upwards; full wet tyres are made from a softer compound, and as they are exposed to cold standing water must be optimized to work at under 40 degrees. As a current wet tyre is exposed to dry conditions, it rapidly overheats and goes off. Looking at a wet/dry combined tyre, the compromise becomes apparent. A tyre that is optimized for dry conditions is likely to have poor wet performance from the reduced running temperature and harder compound alone, whilst those optimized for wet conditions will certainly suffer from the increased temperature and wear in the dry. The wear of the tyre can cause directional instability. This calls for compromise from the mechanics side to support handling in Formula One cars since rapid wear is inevitable in soft compound tyres. The question of going for a hard compound, as already known takes off the traction abilities of the tyre. Possible solutions for an optimum design An optimum solution to designing the tyres for formula one race can be arrived at by researching the factors affecting performance of tyres and the effect of such factors. The following suggestions are made for a competitive tyre design. Providing an asymmetric pattern of the treads on the tyres can render service to both dry and wet conditions. This is achieved by giving higher groove to rubber ratio on the insides of the tyres while having a lower ratio on the outer side. A higher groove to rubber ratio on the inside means better dispersal of water during a wet condition. At the same time the outer tread pattern can aid handling in the dry condition. For precise handling, the rigidity of the tyre is the key. This is achieved by controlling the tread pattern and the contact patch area with the road. Technically, a rigid tread pattern enhances handling and enhances grip in the wet and dry by allowing softer compounds to be used. In order to have a quieter tyre the noise generation due to vibrations and aerodynamic processes (displacement of air through the grooves of the tyres) has to be reduced. The control of noise due to tyre vibrations can be achieved by the following methods; Changes of the contact forces: The contact stiffness determined by the tread material properties, tread geometry, tyre geometry and road toughness has to be as low as possible. It would be of high advantage to have a material whose contact stiffness depends on frequency, while at the same time providing optimum wear and handling. Changes of the tyre response: The tyre mobility can be kept low by the simultaneous increase of mass and bending stiffness. Lower tyre mobility will certainly lead to a lower excitation of the tyre structure. Changes of the radiation properties: The third method is to vary the tread properties and tyre structure properties over the cross section of the tyres. The expected effects by doing this are a. Change of vibration pattern which will result in a change of radiation efficiency b. Modification of the mobility in a way that the contact force will be smoothed out. The control of noise generation due to aerodynamic processes also makes use of the aforementioned points. There are two additional aspects to be taken into account, which are, the local geometry in the contact area and the properties with respect to adhesion and friction determined by tread material properties and road surface properties. CONCLUSION There are problems invariably in the design of all the subsystems of F1 cars. It is important to be aware that these problems are interlinked and one's optimization can help the other. Not all the problems faced in the design of tyres can be addressed without sacrificing its performance. Even worse are the cases of problems which require new materials altogether with special properties. Even as research works continue on the choice of materials and manufacturing methods like vulcanizing etc, there is a limit up to which we can expect possible improvement in the performance of Formula One cars. But having said that, a small improvement in the efficiency, a few microseconds of lap time savings, can mean much to a Formula One car driver. A clear knowledge on how tyres affect the performance of cars can highlight the fact that the performances of the tyres, in turn, are dependent upon the actual conditions of the race much of which we cant exercise control over. So, the bottom line is to keep tracking the conditions and to do extensive studies and to keep updating the technology database in order to keep pace. Works Cited Haney, Paul. The Racing & High-Performance Tire: Using Tires to Tune for Grip & Balance. Pennsylvania, Society of Automotive Engineers Inc, Mar 2003. Read More