The tire problems experienced by Valentino Rossi and Ben Spies at Assen, where great chunks of rubber came off the right side of the rear of the tire, slowing Spies up severely and affecting Rossi so badly he was forced to pit for a new tire, have been the subject of much speculation and discussion since the event. Spies was particularly shaken after the race, the tire problems bringing back bad memories of the 300 km/h tire failure and monster crash he had at Daytona back in 2003, which he still has the scars to show from.
Nearly a week on, and after examination by Bridgestone technicians back at the factory in Japan, we can start to draw a few preliminary conclusions as to the cause of the problems. Bridgestone have issued a press release and briefed the press directly, and riders have weighed in with their thoughts and impressions of what happened. Before pointing fingers and apportioning blame, let us first walk through what we know of what actually happened.
The problems occurred for a select number of riders, though Spies and Rossi were the worst victims of the issue. "I think everybody was blistering the tire, but I was able to finish without pitting," Nicky Hayden said on Thursday. But while blistering is not uncommon, Spies and Rossi were losing major chunks of rubber from the tire, with the rubber coming loose almost from the carcass, rather than blistering at the surface. The direct cause of Spies and Rossi's problems was temperature, Bridgestone finding that the riders who suffered the biggest problems were also the riders with the highest tire temperatures, Bridgestone's Manager of Motorsports Tire Development Shinji Aoki told reporters on Friday. Those higher tire temperatures affected only a very few riders, Aoki said, based on the data which the teams had made available to Bridgestone.
Though Bridgestone put the issue down to a mixture of riding style and setup in the particular circumstances - a subject we shall return to shortly - that does not appear to tell the whole story. Ben Spies told the media on Friday that his setup was nearly identical to Andrea Dovizioso's, and yet Spies had had the problem and Dovizioso hadn't. Though Rossi's set up was a little different to Nicky Hayden's at Assen - "I have two or three differences in the setting," Rossi said - the difference would not seem to warrant the massive difference in tire performance.
The one thing that both Spies and Rossi had in common was that compared to the riders on the same marques, they were spinning the rear tire less. Spies spun the rear less than Dovizioso, and Rossi less than Hayden, yet the tire temperatures of Spies and Rossi were higher than Dovizioso and Hayden. Normally, spinning the rear generates more temperature, though as Nicky Hayden pointed out, only in the surface, not at the core of the tire, which is a much more dangerous situation. "Surface temperature on the outside is really for the heat of the tire," Hayden said. "Sometimes the spinning don't really make a big difference, that's just on top, but once you start moving the construction and it starts working is what can really destroy a tire," he added.
"During the race I spin a bit less than Nicky," Valentino Rossi explained, "usually this creates more temperature, so [the tire problem] is not from that. I have two or three differences in the setting, so maybe it comes from there, because it doesn't come from the spin." The problem had come from deeper down, Rossi added: "My tire in Assen is the opposite problem, the problem come from inside. And in Assen, you have a lot of stress [on the tire] because you have a lot of up and down, so there is a big stroke from the rear, so maybe for this reason something happen." Though Assen is a relatively flat circuit, the banking and the slight undulations around the circuit - built on top of a former peat bog, as is the case with much of the region - could have worked the rear suspension more.
But even this should not have been a problem, with Bridgestone tires developed to withstand those kinds of loads. In previous years this has not been a problem, at least not since 2004, when Shinya Nakano suffered a massive blowout along Mugello's front straight. Since then, Bridgestone had radically increased its testing program, to ensure that the tires were capable of withstanding the pressures of racing before being allowed to leave the factory. But a combination of several factors had conspired to create the problems, Bridgestone told the media.
First and foremost, the philosophy which the championship - Dorna, the riders, the factories and the teams - have asked Bridgestone to follow is slightly different. Tires now warm up much, much quicker, putting an end to the early morning highsides which have blighted MotoGP in the past, causing serious injuries, most famously Valentino Rossi's broken leg at Mugello, but also more serious problems such as Hiroshi Aoyama's cracked vertebrae, suffered in a crash at Silverstone. Bridgestone deny this is the cause of the problem - their aim is to get the tire to warm up more quickly and to create a larger contact patch for the riders -but it seems reasonable to suggest this could have at least some small part to play.
The other major change for 2012 is that the bikes are now 1000cc rather than 800, generating more torque and loading the rear tire more. This has been visible in the tire temperatures, which have increased at every circuit that MotoGP has raced at this year. The effect has been perhaps more profound than Bridgestone will admit. Andrea Dovizioso explained in some depth the problems that have occurred: "The problem is we are really on the limit about temperature," the Italian explained during the press conference on Thursday, "So if your riding style or the setup of your electronics system or you adjust a little bit the setup of the bike to have more weight, it can create a little bit more temperature. With everybody on the limit, this can happen."
On Friday, he went into the subject in even more depth. "I think Bridgestone is the best brand," Dovizioso told reporters, "But we are really on the limit about temperature. So if you make some set up to improve your feeling, but going the way to get more temperature, you can have the problem which Ben and Valentino had. Sure the weight distribution of the bike is more important, but the truth is we are really on the limit. You can't ride how you want, you can't make the setup how you want, you have to follow always very well the temperature and what Bridgestone requests. It's not so good but it's the same for everybody."
Dovizioso explained where the changes had come from as well. "What the Bridgestone guy said is the reason we have more problems and we are more on the limit this year that last year is because in the Safety Commission, many riders complained about the warm up of the tires and many times we couldn't use the hard, so they have to bring really soft tires." While emphasizing that he could not offer a technical explanation, Dovizioso did give his opinion of what had happened. "My feeling is the tire is different this year, not just softer. Also the difference I think is too big. What they changed is really good, because we have no problem about the warm up of the tires, so this is really important, Bridgestone made a good job. But maybe they followed too much what some riders requested, and they made too big change, and maybe the mix is too much. When I speak about too much, I think how much too much is very small, but when everybody is on the limit, this can happen. This is my opinion, but I don't know if it's true. But the problem is they already decided the tires for a few races, and this is what the safety commission requested, and that's why we have this type of tires."
The Assen circuit itself, and the weather conditions there during the race weekend, had also played a major part. The camber which is a key part of the Assen track had worked the tires hard, and though that had been factored in by Bridgestone's engineers, the higher temperatures than last year - track temperature was 21°C higher during the 2012 race than it was in 2011, 37°C vs 16°C - had perhaps pushed the tires over the edge. But Bridgestone were not entirely to blame for the softer spec tires falling short of the tire performance window. At the beginning of the season, when Bridgestone were drawing up the tire allocations, they had prepared two specs of tire to choose from ahead of the race. "At the beginning of this year, we recommended the harder tire," Shinji Aoki told the media, "But finally, when we discussed the Assen allocation with the Safety Commission, Safety Commission request a softer spec. We requested hard and medium, but finally we discussed many times with the Safety Commission, because last year, Assen was so cold, many riders complained about warm up performance. Finally we agreed with the Safety Commission, and took the medium choice. But the hard spec we had would have had much better performance against the heat."
So a number of factors colluded together to cause the catastrophic problems experienced by Rossi and Spies. The problems resemble a cascade failure, with a sequence of choices and conditions creating the problems. The Safety Commission, with Loris Capirossi guiding them, elected to take the softer of the two constructions for Assen. Temperatures at Assen were higher than expected, pushing the tires to the very edge of their temperature performance envelope. The track itself is tough on tires, the camber and banking adding extra load on the carcass, making it flex and generating more heat. And perhaps either riding style or setup meant that the added mechanical grip that Rossi and Spies had, which meant they were spinning the rear less, created more load through the tires and worked the carcass harder. The heat generated probably caused the rubber to separate from the carcass, creating the chunking.
An exceptional set of circumstances, which should not be repeated very often. For Mugello, Bridgestone are already flying in a harder spec of tire, at considerable expense - one of the downsides of a spec tire is that costs are kept to a minimum, with tires moving from Japan by surface transport, and planned right at the start of the season, before there is even the slightest inkling of what the weather might do. The harder spec for Mugello, which is expected to be very hot, should provide a good enough safety margin at the circuit. "At Mugello, it's going to be really hot and we'll be going really fast, so we need options for there," Spies said. "It's good that they're taking that into account."
All this presupposes that the fault was not down to a manufacturing fault, something which Bridgestone explicitly denies. Casey Stoner was far from convinced, and had some harsh words for the Japanese tire firm. "It's simple, they've got faulty tires," Stoner said on Friday. A day earlier he had expressed his doubts about his own tires at Silverstone, as well as the tires at Assen: "We went to a track like Silverstone and we really struggled, but at the same time we don't know if there's tire faults going round. In my opinion at Silverstone, there was something wrong with the left side of my tire, and as we've seen in Assen immediately the week after it was sort of confirmed that there are problems with the Bridgestone tires, but you'll never hear them admit it."
Bridgestone's unwillingness to admit when they had issues had been a problem since he first switched to the brand in 2007, Stoner said. "They'll always cover everything up, they have since I raced with them back in '07, they've never admitted to anything being wrong with the tire, they'll always say, you put too much temperature in, you did this wrong, you did that wrong, but they'll never actually admit it themselves," he said on Thursday.
Valentino Rossi was not disposed to believe Bridgestone had a manufacturing problem, saying that he had to take on faith what he was told by the Japanese company. "If Bridgestone says there is not a problem with the tire, I trust them," Rossi said on Thursday. Asked about this the next day, Casey Stoner took a far more cynical line. "Do we trust them, you know?" he asked rhetorically. "Their tires are getting worse, the lap times year by year are getting worse. Technology year by year is improving and we're getting slower. It's harder for us to beat lap records. They will never admit there is something wrong with their tires, which is the biggest problem. It's disappointing."
Bridgestone manager Shinji Aoki rejected Stoner's accusations. For a start, the lap times showed that the tires were still improving, he said. "As you know, lap time is not getting worse," he told reporters "I think at this moment, now everybody has the same time." Aoki added. "Before when we had tire competition, and some companies were supporting riders, lap times were more up and down."
Aoki dismissed Stoner's accusations that Bridgestone would never admit when they have a problem, joking rather cuttingly "At this moment, it sounds like Casey is not happy." Aoki then stated that Bridgestone had never had a tire problem, a claim that was hard to back up as the assembled journalists produced a relatively impromptu list of tire problems that had occurred with the Bridgestones. Nakano 2004 - after which Bridgestone had massively extended its testing program, Aoki said - and Kenny Roberts Jr in the same year. Then Dani Pedrosa in 2009, suffering problems with the front at Barcelona. Aoki could not recall that incident, he said. It spoke in Bridgestone's favor that the list of failures the press could assemble was very short. But a short list is still infinitely longer than zero, as Aoki implied when he claimed that Bridgestone had never had a problem.
Where does the truth lie? It is hard to say. Certainly, there is much merit in the arguments put forward by Bridgestone explaining the possible causes of the failures, and the logic is hard to argue with. However, the only basis we have for believing that the problem was not caused by a manufacturing fault is the word of Bridgestone themselves. This is the weakness of a spec tire series, with no one to watch over those responsible. It all comes down to the question put by Casey Stoner: Do we trust them?
The whole discussion has been unusual, with Bridgestone so far having proven to be an extremely reliable and consistent partner for MotoGP. Now we have a bit more drama injected, more reminiscent of the other motorcycle racing world championship. "It seems like I'm back in World Superbike, where there was a problem with the tires every week." Cal Crutchlow joked when the subject came up. So it isn't just MotoGP, at least...