Friday, 4 November 2011
Understanding F1 car - V2: Tyres
FIA moved to a single tyre supplier in 2007(Bridgestone) but, even now, optimizing the car-tyre balance is something of a black art.
An ordinary car tyre is made with heavy steel-belted radial plies and designed for durability - typically a life of 16,000 kilometres or more. A Formula 1 tyre is designed to last for, at most, 200 kilometres and - like everything else on a the car - is constructed to be as light and strong as possible. That means an underlying nylon and polyester structure in a complicated weave pattern designed to withstand far larger forces than road car tyres.
F1 has a single tyre supplier, with all teams using identical Pirelli rubber. The advantages of this, instead of dispose over multiple tyre suppliers, include closer racing and reduced testing and development costs.
The specifications of Pirelli tyres are differentiated by the colouring of the sidewall lettering:
super soft - red
soft - yellow
medium - white
hard - silver
wet - orange
Harder compound tyres will be more durable than softer compound tyres, meaning that the driver can complete a greater number of laps before the tyres lose performance and they are forced to make a pit stop. The harder compounds will provide less grip than the softer compounds, meaning that the driver will not be able to go as fast on each of the laps they make. The choice of tyre compound is therefore a compromise between durability and grip. Choose hard and you'll be able to stay out longer than your competitors. Choose soft and you'll have to pit earlier in the race but you'll be going faster than they are and may be able to make up the difference. The physical explanation of the difference between the hard and soft compounds is the degree to which the rubber molecules interact with the track surface.
SLICKSlick tyres are the ones that F1 drivers use most of the time. A normal slick tyre actually has no tread pattern at all. This is because in dry conditions the aim is to get the maximum grip from the tyre and this is achieved by having as much rubber in contact with the racetrack as possible.
The wet tyres, which are characterised by grooves in the tread pattern, come in two types: full wet tyres, for rain, and intermediates and the two tyres have in common the same compound.
The wet tyres have deep grooves in them, with channels designed to expel water on full wet asphalt. These tyres are similar to a road car tyre, and are designed to expel more than 60 litres of water per second at 300kph. A road car tyre can only displace about 10 litres of water per second, at much lower speeds.
Intermediate tyres are exactly what their name suggests - a compromise between a full wet and a fully slick tyre. They have slightly shallower grooves that are cut in a different pattern and remove a fair amount of water from the racetrack surface while also providing a decent level of grip once the track has dried. These are the tyres that are used most often when weather conditions are bad. Only in absolutely torrential conditions where there is continuous rain are the fully wet tyres needed.
The best tyre pressure is one that results in the greatest area of the "contact patch" (the area of the tyre that makes contact with the track surface). An under-inflated tyre will have a large contact patch but will not support the car very well, increasing the risk of the bottom of the car scraping the surface of the tarmac. On the other hand, an over-inflated tyre will have a small contact patch and is therefore not providing the maximum level of grip.
A typical tyre pressure in F1 is approximately 1.1 bars, whereas a normal road-going tyre pressure is in the region of 2.2 bars. This is because a F1 car weighs only 600kg and the average family car about 1000kg, therefore less pressure is needed to support the lower weight.
Formula One tyres are normally filled with a special, nitrogen-rich air mixture, designed to minimise variations in tyre pressure with temperature. The mixture also retains the pressure longer than normal air would.
The moisture content of air is variable depending on the local weather conditions and this differs considerably between some of the exotic locations on the GP calendar.
The air is a mixture of nitrogen (78%) and oxygen (21%). Oxygen gas is far more reactive than nitrogen and at the high operating temperatures of F1 tyres (> 100°C) the oxygen reacts with the tyre, reducing the total pressure inside. Using pure nitrogen removes this problem and tyre pressures remain far more consistent.
The tyre manufacturing process begins in the rubber tree plantations of South-East Asia. A sloping cut is made in the bark of the tree, from which a white milk-like fluid called latex bleeds and is collected. Cutting the sloping incision Collecting the latex. The latex is combined with carbon, oil, sulphur and other chemicals and undergoes a number of processes, many of which are industrial secrets. All this produces black sheets of rubber. The rubber sheets are heated and thin lengths of nylon, polyester or even steel are woven into them to give them rigidity. These woven sheets form the main basis of the tyre. The inner rim of the tyre is called the "bead ring" and is produced separately to the main tread of the tyre. The bead rings are formed by coating thick wires with the rubber mixture and coiling them up around a template. The woven sheets and bead rings are joined together and finally the tread pattern of the tyre moulded on top. The tyre produced is not yet complete and is called a "green" tyre. The tyre is then Vulcanised by applying heat and pressure in special machines to produce the finished F1 tyre.
One of the key steps in the manufacture is called Vulcanisation, a process invented by Charles Goodyear in 1839. Natural rubber (chemical name polyisoprene) consists of long hydrocarbon chains which are randomly intertwined with one another but have no molecular links between them. By mixing molecular sulphur (a yellow solid) into the natural rubber (which is a sticky, gooey substance) and heating the mixture, sulphur cross-links are formed between the rubber molecules. This hardens the rubber and gives it the qualities of strength and elasticity that one associates with rubber tyres.
The development of the racing tyre came of age with the appearance of 'slick' tyres in the 1960s. Teams and tyre makers realised that, by omitting a tread pattern on dry weather tyres, the surface area of rubber in contact with the road could be maximised. Formula One cars ran with slicks until the 1998 rule changes came into effect, and new tyre standards were introduced in an attempt to improve the spectacle of Formula One racing by reducing cornering speeds. This led to the familiar sight of 'grooved' tyres, the regulations specifying that all tyres had to have four continuous longitudinal grooves at least 2.5 mm deep and spaced 50mm apart. These changes created several new challenges for the tyre manufacturers - most notably ensuring the grooves' integrity, which in turn limited the softness of rubber compounds that could be used.
Between 1998 and 2008, regulations required the tyres to 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). They can be no wider than 355 mm and 380 mm at the front and rear respectively and the maximum diameter is 660 mm (670 mm for wet tyre). Slick tyres were reintroduced at the beginning of the 2009 season along with aerodynamics changes intended to shift the balance towards mechanical grip in an attempt to increase overtaking.
On 2 November 2009, Bridgestone announced their withdrawal from Formula One at the end of the 2010 season. Michelin, Cooper Avon and Pirelli showed interest in taking over the role of tyre supplier. In June 2010, it was announced that Pirelli would be the 2011 sole tyre supplier and would receive a 3-year contract. During August 2010, Pirelli commenced its test programme with the Toyota TF109 at the Mugello Circuit with Nick Heidfeld as the test driver.
With the sole tyre supplier having been changed from Bridgestone to Pirelli, the rules were the same as the 2010 season rules concerning the tyres. All teams still were required to use each type of dry tyre compound supplied in the race, and drivers that made it through to Q3 still had to use the same tyres they used to set their fastest qualifying time with to start the race. However, the way of denoting different tyre specifications was changed. Rather than a green stripe denoting a softer compound, for each tyre specification, the lettering on the tyre would have a specific color. The hard compound would have silver lettering, the medium compound would have white lettering, the soft tyres would have yellow lettering and the super-soft tyres would have red lettering. For the wet tyres, the intermediate tyres would have light blue lettering and the full wet tyres would have orange lettering.
Both compounds, prime (harder) and option (softer) compounds must be used in a dry race, failing which a driver will be disqualified. If a race is suspended without both tyres being used, a 30 second penalty will be imposed. This requirement is waived should drivers use wet weather tyres.
At each Grand Prix every team is given access to two specifications of dry-weather tyre. Unless conditions are wet, drivers must use both specifications during the race.
Over the race weekend, each driver has access to 18 sets of tyres:
- 6 sets of the harder ‘prime’ specification
- 5 sets of the softer ‘option’ specification
- 4 sets of intermediate tyres