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05/09/2011
From the track to the road. Or vice-versa?

The development of the tyre

Many tyre manufacturers are investing in competitions. Race tracks are an important test bench for new technologies and an effective vehicle for promoting products and image

Paolo Ferrini

Whether or not you are enthusiastic about sports cars, in the 21st century the axiom according to which the winner of a race is also good for everyday use, still applies and is very current. Even when it comes to tyres.

 

Audi's tenth victory at the 24 Hours of Le Mans coincides with Michelin's fourteenth consecutive win (making a total of 20!) on the classic De la Sarthe circuit. And Pirelli's return to Formula 1 has reopened the debate about the usefulness of competitions for mass production. In other words, the talk is again about car races as a test bench for new technologies, for promoting products and image and also as an essential impetus for technical development.
One thing is certain. Whether or not you are enthusiastic about sports cars, in the 21st century the axiom according to which the winner of a race is also good for everyday use, still applies and is very current. Even when it comes to tyres. Pirelli knows something about this. After winning the first edition of the Formula 1 World Championships in 1950 with Nino Farina and the Alfa Romeo 159, it was absent for twenty years but returned to the world of Grand Prix as the exclusive supplier of tyres for all participants.
Adding weight to Pirelli's return to Formula 1 were technological impact and the huge re-establishment of image and fame guaranteed by a speciality that today has about 2 billion fans.
From this point of view, the Italian manufacturer is in good company. In addition to Michelin, which for many years has linked its brand to the great endurance classics (competitions that demand tyres that are able to combine high performance with less wear), Yokohama, Firestone, Dunlop, Hankook and Goodyear, just to mention a few at random, are also convinced about the importance of taking part in competitions. After all, they are the exclusive suppliers, respectively, of the WTCC, Formula IndyCar, Open GT European championships, DTM in Germany and the NASCAR championships in the United States. At this point, there can be no doubt: a commitment to sports "pays" from the point of view of promoting products and brand image. But what is the technical connection between racing tyres and the ones we mount on our cars?
First of all, there are racing tyres and then there are racing tyres. The need to equip very lightweight, powerful vehicles with sophisticated braking systems and particular layouts, like the current one-seat used in Formula 1, and the regulation 13 inch wheels, have led to the creation of tyres with big shoulders that will best handle load transfer. On the other hand, in competitions for sports cars and mass produced cars, the wheels are larger in diameter and, above all, have low-profile tyres apparently more like those on modern vehicles for normal use. In this case, the GTs that participate in the FIA GT championship and the prototypes competing in the 24 Hours of De la Sarthe, have 18 inch wheels, whereas the saloons in the WTCC have 17 inch wheels.
"This decision is based on various reasons, primarily because of the greater weight of tour and grand tour vehicles, their higher barycentre and, as a consequence, greater load transfer that causes them to roll, pitch and go nose up" explained Giorgio Bellotto of Bellotto Racing Service, a company that for many years has specialized in tyre services for competitions. "But perhaps the main factor is the need to house large braking systems". This means that the covered wheels on racing cars have a wider diameter so that in many ways the tyres are reminiscent of the super-low profile tyres on many of today's mass produced vehicles.
And that brings us back to Formula 1. Strange as it may seem, the origin of the PZeros that this year Pirelli is using in F1 is quite unusual. In their case, technological transfer was from the road to the track, in the sense that the designers took advantage of the Italian manufacturer's decades of experience in developing high performance tyres. "Even though they are lighter and five times stronger, the new tyres for F1 and those for supercars share the same calculation and simulation model as well as part of the resins used in the compounds", Pirelli explained. 

 

• Endurance tyres 

 

Racing tyres are not all the same because they are treated differently. In Grand Prix Formula 1, tyres are changed two, three and even four times during a race of an hour and a half, but in endurance competitions a racing set can be used for the same length of time (and sometimes longer) without losing efficiency, thereby contributing to a greater chance of victory because they are more durable and less time is spent in the pit. Which was the case of Audi. It owes some of its success at the 24 Hours of Le Mans 2011 to the best management of the Michelin tyres and the ability of the Audi R18 to make them last slightly longer than did the Peugeot 908.
Unlike F1, electric blankets are not permitted in endurance competitions, which leaves it up to the driver to use the most appropriate method to get the tyres up to temperature as quickly as possible from cold.
Prototypes and GTs frequently race with extreme camber angles that put stress on the inner part of the tyre on the straight. The result: tread lift is more than likely. Just as it is more than likely that tyres will pick up microscopic pieces of rubber left on the asphalt by the tyres of the many vehicles in the race (56 at Le Mans), which make the steering wheel vibrate abnormally and the driver think that there are serious technical problems. 

 

• Wide and low, tyres that set the trend 

 

After remaining more or less the same for about forty years, in the early ‘60s tyres gradually began to change shape and they became increasingly lower and wider, and price lists nowadays frequently include ultra-low profile 25 series, or "bar 25", where the height is 25% of the width.
In a certain sense, this trend was sparked off by car manufacturers when a number of cosmetic demands and the need to house larger braking systems (due to the constant development of car engines and suspension) forced them to gradually increase wheel diameter to give a wider support base and thereby improve performance on the road. But the use of wheels with increasingly wider diameters made it necessary to contain the overall diameter within the wheel arch. This led to the need to reduce tyre shoulders or, rather, to continue to reduce the aspect ratio.
In some ways, using low-profile tyres has the same effect as widening the axle track: increasing tread width gives greater contact with the ground and makes the vehicle more stable also with the strong lateral stress characteristic of high speeds when cornering. Lowering the side and increasing tread section also gives the tyre more rigidity to the advantage of rolling resistance, grip when cornering, and braking performance.
The use of low-profile tyres has also allowed car manufacturers to compensate for increased vehicle weight (due to the requirement, for example, to increase safety equipment or soundproofing), but this has led to higher tyre pressures. The other side of the coin is the need to pay more attention to pressures and "less sensitivity", which could create problems for less expert drivers. "The lower sidewall lessens the feeling that grip is being lost", explained Paolo Marconati of Yokohama Italia. "A low, wide tyre is very stable, but it gives the driver less "warning" when it is about to lose grip".
Nevertheless, the fashion for increasingly low profile tyres seems to be irreversible. Especially for high performance models.
 

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