A Beginners Guide to WTCC Tyres.

Most of the WTCC truckies are also responsible for tyres. So I have compiled a bit of an insight for those who are interested.

Firstly, we all use a control tyre, supplied by Yokohama. Only 2 types of tyre are available, slicks and wets. No other sizes or makes are allowed. The slicks are 240/610R17 for the ADVAN A005 and the wets are 240/610R17 for the ADVAN A006. Each car can use a maximum of 12 new slicks and can also use 8 of their best carry over tyres from the previous race. Some flexibility is built into the regulations when the season starts and when we go to new tracks or fly away events, but I am not going to list all the permutations available here. IT WILL BORE YOU.

Tyre declaration sheet.

Scrutineers.

Tyre scanners and yellow bar code on the tyre.

Once the tyres are fitted, the bar codes on the tyres are scanned by Yokohama. The teams will then collect their tyres and must write down all the bar code numbers, which are then given to the scrutineers. Later on, the tyre scrutineers will visit each team, scan the tyres again, to ensure that they match the tyres declared by the teams. 
The teams will now go through the arduous task of cleaning and giving each of their race tyres its own number,eg, 1,2,3,4 etc. And possibly marking FL(front left) or RR(rear right). As we have many different nationalities, these markings will differ according to which language they speak.

Cleaning and marking tyres.

Some teams do not bother with any tyre balancing. Others balance the rim before it is fitted with a tyre, and some teams balance the rim after a tyre has been fitted. I went testing with a team sometime ago and we put lots of tyre weights on the rims and monitored whether the driver could detect the vibrations. The results were that a tyre can produce quite bad vibration before the driver becomes very concerned. REMEMBER, these are touring cars. NOT, sensitive, ultra lightweight, single seaters. All teams will constantly check the rims during the race weekends to make sure that they are still round. These cars use alot of kerb in some of the corners, so a few damaged rims are to be expected.

TPMS fitted to a rim

Tyre pressure sensors,(TPMS), can be also fitted. These will monitor the tyre pressure inside the tyre, each lap. It normally takes a tyre several laps to reach its optimum pressure. Data is sent from the TPMS to the enginners laptop via the car. The tyres are normally inflated to a cold pressure.e.g. 1.6 Bar. Then when the tyre has been put into its tyre warmer for approximately 1.5 hours, a tyre pressure reading is taken and then a small amount of air will be taken out.As the tyre temperature rises, so does the tyre pressure. The engineer has to calculate what tyre pressure he wants to achieve for optimum performance.
ALL TEAMS HAVE DIFFERENT WAYS OF DOING THIS PROCEDURE AND ENSURING THAT THE TYRE HAS THE CORRECT AMOUNT OF AIR BEFORE THE CAR GOES ON TRACK.

Tyres in the tyre warmers.

The question of whether to use air or nitrogen to inflate the tyre, is a tricky one. Again, some teams do and other teams do not. Many races are won using normal air. The air may pass through an air dryer before it enters the tyre, to try to take out as much moisture as possible. Air is a mixture of Nitrogen(78%) and oxygen(21%) Oxygen is far more reactive than Nitrogen and at high operating temperatures, the oxygen reacts with the rubber of the tyre, reducing the total pressure inside.Water particles in the air upset the contraction and expansion as a function of temperature which also makes the tyre pressure unpredictable. Nitrogen however, will not absorb any appreciable amount of water, so your tyre temperature should not fluctuate. But if you use Nitrogen, you should first inflate the tyre with Nitrogen, let it all out, then re inflate with Nitrogen before putting in the valve core.
This is called "purging". The extra time and effort to do this is quite considerable for the teams who use this procedure. If you do not purge the tyre first, you will still have a small percentage of air mixed with the Nitrogen.

Tyre warmer control box.

The tyre warmers will sometimes be set to a maximum temperature,e.g. 80 degrees Celsius. Some teams will will turn up the temperature of the tyre warmers for maybe another 15 minutes before the car goes out. Teams will try to put the tyres through a maximum of 3 heat cycles while they are in the tyre warmers. More than this can be detrimental to the tyre. Every team seems to do it differently.
A similar procedure will be used for the wet tyres.

Ready to use a heat gun to scrape the tyre clean.

Another job that is done to the tyres, after they have been used, is tyre scraping.
This gives a team chance to clean up the tyre surface of old rubber that has picked up on the tyre, usually as the car comes into the pits. The race engineers can also inspect the tyre service when it has been cleaned up. This is not always necessary as a track that is clean will not have lots of old rubber laying on the track.

Old rubber which has been cleaned off a tyre.

All of this care and attention to the WTCC tyres will still give the race engineers some surprises. All they can do is try to follow the basic rules and formulaes and then make adjustments on the day of the races.
The optimum tyre pressure for each car is forever changing. Ambient air temperature, track surface temperature, the suspension set up of the car, or hitting the kerbs on the corners very hard. All of these can affect the tyre and its performance. Also, drivers all have different driving styles and like their car to handle in different ways. Do they want a bit more oversteer or understeer in a corner? If you look at the diagram below, you can see how the tyre pressure can affect the handling of the car.

Adjustments	Decrease Understeer	Decrease Oversteer
Front Tyre Pressure	Higher	Lower
Rear  Tyre Pressure	Lower	Higher

This piece you are reading is really only an overview of what happens to a WTCC tyre. Without trying to confuse you with too much technical stuff.
Tyres may be little, round, black pieces of rubber but they demand and require a lot of care, love and attention. Race engineers can put big demands on the truckie in charge of the tyres. It is a very underrated aspect to keeping the car on the track. A good tyre man is as essential as all of the other team members.