There is no need to dwell on the tire events which led to the rearrangement of the Rio Hondo race, these having already largely made the headlines on the subject.
MotoGP is now heading to the American event on the COTA circuit which in turn offers its share of difficulties.
The circuit:
This wide route (15m) will not present the same grip problems as Argentina and the scrubbing of the track will be easier. It is also slower and has many breaks in rhythm: apart from the sequence of turns #2 to #8, it is the “stop and go” circuit par excellence.
With drivers spending 32% of the time braking (26% for Rio Hondo), rear tire heating will be more limited. It must also be said that although the stresses due to accelerations are more numerous, they are also shorter and do not continue as much over the angle.
The layout of the route is long, 5513m, and it has 20 turns distributed fairly evenly: 9 right turns and 11 left.
The GP of the Americas therefore risks taking place in a more orderly and less folkloric manner than that of Argentina… But… But…
But, regarding the tires, the meeting will be tough too!
Of course, the rear tire seems less stressed, the front on the other hand...
First of all, there are two big brakes where the MotoGP will go from around 345 km/h to 60 km/h and from 315 km/h to 65 km/h. And if the left turns are for the most part sharp and brief, the right turns are much more prolonged, which leads to a difference in the heating of the rubber on the shoulders of the front tire, this having had many consequences in racing in the past, with Bridgestone…
The past :
Historically, we witnessed a destruction of the front tire affecting many competitors in 2014.
If in 2013, the wear was pronounced, 2014 gave rise to a controversy when Bridgestone decided not to use this year's rubbers, more rigid, but again the 2013 tires which had already endured the ordeal...
It must be said that Lorenzo had complained about this new tire situation, preferring the flexibility of the 2013 tire, and it seemed that the Japanese manufacturer had acceded to his wishes, to the great displeasure of Marquez, Rossi, Smith... all fans of the rigidity.
Let us point out that these rubbers were equipped with an “anti-heating” treatment which gave Bridgestone one argument, delayed production of the 2014 models, unconvincing, added another…
However, the ordeal will turn into a disaster for Bridgestone and the criticism will be all the more harsh as the aforementioned controversy loosens tongues. Even Rossi, brand ambassador but 8th in the race due to the literal melting of his front tire, protested vehemently, citing the safety of the drivers...
The explanation comes from the fact that although the GP was newly added to the calendar in 2013, the pace of the race was significantly faster in 2014 (10 seconds less), thanks to the use of data from the previous year. ; the puddings were not able to follow this evolution…
The analysis of Bridgestone technicians will not attract much attention; one of the major braking events is done uphill (the track is hilly), most of the riders adopted harder fork springs to be more efficient, which changed the way the front rubber worked and caused this destruction...
To meet COTA requirements (braking, rapid angle changes, left turns with short but significant pressure), the 2013 model tires have adopted a relatively high pressure and in addition to the heat gained by absorbing the kinetic energy of braking, the The footprint in contact with the ground is too small in right turns, causing the surface of the tire to heat up on that side: the result is spectacular:
Fortunately, the year 2015, which will see the use of stiffer tires (same carcass as 2014 and fairly resistant rubber), will cause pronounced but not prohibitive wear of the casings during the race.
This story nevertheless teaches us that not all competitors are affected in the same way by the wear of their tires and that the key point concerning the temperature of the front tire is braking, or at least, the way of braking...
But speed on this type of “stop and go” circuit also depends on the control of acceleration, linked to power and… cutting-edge electronics, something owned until this year by Honda.
Braking:
Let's look Brembo data : Marquez is renowned for being a brakeman from beyond the grave. However, the data from his braking shows that he uses his front brake to constrain his fork but not in as radical a way as we think: he only brakes with one finger and uses much more than the other riders its rear brake. If its initial pressure remains significant, it is brief and is quickly reduced by the use of the rear brake, this explains why its Honda remained equipped for a long time with carbon discs of 320mm in diameter while the 340mm were adopted in the majority by its competitors…
Once the caster is reduced by this initial pressure and the constraint of the fork, Marquez puts his rear into drift using the engine brake used in conjunction with the rear brake, and this relieves the pressure stressing his front tire, which takes this way less temperature...
Comparatively, Rossi uses 4 fingers to apply braking which is certainly very linear, but which with the large discs is close to the limit of grip of the front tire and causes it to take maximum heat...
To conclude:
If we look carefully, in 2013, Marquez wins, followed by Pedrosa (light driver = less stress on the flange), followed by Lorenzo (not a powerful braker but adept at entering fast curves), followed by Crutchlow (whose braking is powerful but very brief).
Rossi is sixth.
In 2014 Marquez wins using the hard rear tire (the only one), followed by Pedrosa, Dovizioso and Rossi, big brakers, are 7th and 8th…
In 2015, big progress in acceleration and electronics for Yamaha (seamless) and Ducati, while the front tire is more rigid; Marquez is still ahead, but Dovi is only 2 seconds away and Rossi 3 seconds…
To summarize, to win in Austin, you need a front that can handle the heat and a rear that can drive and get back up to speed quickly. Recent developments show that the marginal advantage due to braking is reduced compared to that of controlling acceleration.
Outlook…
On the braking side, Marquez, the only one who manages to brake on the corner, as well as Pedrosa and Lorenzo who will have less heat, will therefore be the least disadvantaged with the Michelin front tire in terms of wear. The grip, which is not yet quite at the level of that of the Bridgestones, will allow Rossi and its powerful in-line braking to be fast.
The choice of hardness would probably be very different between these drivers if COTA did not impose rapid changes of angles, very sharp, when passing through the 3,4,5 curves, which precisely require rigidity.
In terms of acceleration, the Ducati of Dovizioso and Iannone are a step above the Yamaha, themselves a little superior to the Suzuki and Honda for the moment...
Marquez is the ultra-favorite in this GP of the Americas, victory of which has never escaped him. He is also the rider who seems to use the front Michelin the best to the point of being able to overtake when braking but, with unique electronics which perform less well on the acceleration of the Honda, he could be seriously challenged this year.
The battle between Rossi and Lorenzo, who will be keen to catch up, should be interesting.
A Ducati victory at COTA would make up for Argentina's lack of success... provided that the brand's riders stop shooting each other in the face.
