Choosing Tyres

First time I ever took an interest in WRC was after i watched 'engineering the world rally' on Discovery Turbo this week. I was wondering how they chose which tyres to use for which conditions between Soft, Hard and Medium.

Any Help?

Welcome to the forum!

Usualy they have weather crews out on the stages and of cours during the recce the look at the base of the road, it also depends on the road positon if you are first on the road you have to use a softer tyre, furter back you need a harder tyre as the road can tend to be like tarmac in some places especialy in Mexico. But you have to chose what tyres you want to bring for the rally one week ore something (longer on the long stint rally's) so you can lose the rally one week before it's even started. so you can end up having to use rain tyres in suny weather and 30 degrees.

Welcome to the forum.. Subarunorway covered it pretty well.. You must be talking about Stephan Sarizans unusual choice on the Monte Carlo? Basically ground/air temperature, starting position and future stage conditions for that leg (as per Sarizan) as well as stage length.

Not only are there soft/medium/hard compound options but wet/intermediates/dry and many variations of tread cuts to suit different surfaces and conditions as well as long and short studded (steel studs) for driving on snow and Ice.

I think Marron also referencing to the Pirelli man, who had different visions than the driver and the team specialist from SWRT. In the Japan special Pirelli wanted to force Atkinson tyres he did not want. Atkinson felt secured with his choise, based on the recce, the condition and how the car reacted, and sticked to huis choise, which did not please the Pirelli man. And Atkinson performed better on his tyre choise.
The driver has to have confidance in his car and the tyres, and he knows how the car reactes. The tyre man has to bring his vision, his knowlegde of the components of the tyre and how they react on the long runs. Together wit the fresh information from the weather crew, the expectations of the weather for the upcomming stages the team decides which compound (soft, hard, with a number sellection in case of Pirelli), how many cutes their have to be made in the tyres to deal with the water/gravel/mud.
So it is *driver *tyre man of the team * tyre man from Pirelli *the weather crew *the weather specilist who stick together their information and knowlegde and come up with a decision of which they hope wil be the best average perfomance in all the upcoming stages.

Welcome to the best forum around.

Another consideration for tyres is their construction. The physical way is has been made. Not only is the rubber compound different but the way the layers of reinforcement are laid, width of tread, total width of tyre, the pattern of cuts in the tread & other little things.

They are often 'hand made' to some extent to ensure quality control. Testing & computer simulations predict how the design of a tyre is made. It is ongoing & it can vary from rally to rally to some extent. That is why, to keep the cost of development down, a control tyre will be introduced next year. Only a select few variations of tyre will thus be made.

Also you might not know but a rally tyre is Assymetrical. That means that it is built to fit on only one side of a car, Left or Right & rotate in one single direction. This means that tyres can only be swapped from front to rear on that side, unlike most passenger road cars.

Once fitted to a car, air pressure & the tread also comes into mind. Extra grooves can be cut or widened to allow better traction in muddy conditions. Spikes in snow are very important with varied choices of sizes.

With so much to choose from, that is why the Factory Expert is required to give his advice according to what they have made & have ready. This is opposed to what the Team Engineers know & what the Driver wants. The 'same' tyre at one event could vary from the 'same' tyre at the next, due to changes in batches & improvements made.