All the teams knew from the Sprint that early tire drop would likely have strong influence on Sunday’s results—even if everyone switched to the not-all-that-different medium rear. Up to now, the British MotoGP race has had springtime dates, but here we are in August—race day track temp was 44C, but a year ago springtime it was 24. Raul Fernandez on a Trackhouse bike led a 1-2-3 Aprilia sweep, winning by two and a half seconds over Jorge Martin, with Marco Bezzecchi, closely following in third.

Top Ducati was that of Alex Marquez, fourth. Brother Marc, so successful at Sachsenring, had early tire drop in the Saturday Sprint such that his laptimes sagged, from best to worst, by 4.9 seconds. Toprak Razgatlioglu’s Sprint drop was 4 seconds.

Sunday’s race was therefore a contest of rear tire temperatures. Below a certain threshold (accidentally discovered by Fernandez in the Sunday Warm-Up) there was some drop, but not nearly as steep as at higher temperatures. The Aprilias could operate below this threshold, but most others could not.



Marc’s opinion of the rear tire problem was that, “…when you have graining, it’s like the rubber is not working in a correct temperature.”

Graining produces curved “beach marks” on the tire’s surface, and the tire people tell us this means the compound is not strong enough. Riders who did well spoke of taking care with the throttle. Fabio Di Giannantonio, sixth on a VR46 Ducati, said of the Aprilia, “Our bike is quite complete, but they have this little better entry of the corners that allows them to be more relaxed on the throttle and then manage better the tires.”

Alex Marquez said his encounter with this high temperature grip loss in practice gave him a working tool for rear tire management – especially at the end.

Fabio Quartararo (factory Yamaha) wasn’t a high finisher (16th, and last) but commented, “…when you have more grip, you can play more with the throttle and bring the temperature a bit lower.”

Jorge Martin (factory Aprilia) explained his management succinctly: “Not opening the throttle 100%, trying to wait until the grip is there.”

Ai Ogura (the other Trackhouse Aprilia), second in the Sprint, made an error early in Sunday’s race. His description; “A bit more angle with the same amount of brake pressure.”

Without this error it could well have been Aprilia 1-2-3-4. Ogura had reckoned Fernandez for the win: “When I saw his data after the Warm-Up today, I could see definitely it was his day and my target was to finish P3, P4, more or less.
Fernandez had seen that tire behavior was more constant at lap-times of low minute-fifty-nines, and that’s how he lapped on Sunday.

Because real events must be transformed by imaginative persons into news (which is invariably more exciting) people were tempted to say “Ducati is now the second power, for Aprilia rules.” But what if Sunday’s tire drop temperature threshold had not been located precisely between Aprilia and Ducati? Then it might have appeared that some weird tire behavior had slowed everyone.



This is partly a remnant of the days of corner-speed tracks and point-and-shoot tracks. Yamahas were engineered for corner speed, Honda’s for point-and-shoot. Today it is more like Aprilias produce downforce that boosts grip more the faster they go (that is, on tracks with long sweeping corners), while the Ducatis, although they have gained corner speed in recent times, remain more optimized for the “Formula One squiggles”—small corners in which hard braking, compact turning, and early hard acceleration remain effective.’

Classic modern era tire drop was described to me by a tread rubber compound engineer as the result of the tire’s exposure to mechanical stress. Normally, clusters of rubber-reinforcing carbon black or silica particles exist in tires fresh from the factory. But after time in stress cycling, those particles move away from each other in some degree, causing changes in tire performance.



Yet at Silverstone, we see that temperature is very likely involved. First, we know that track temperature was high, and with frequent accelerations, seconds spent at high lean angle in fast corners, the deformation of the rubber is high. That, combined with rubber being an inefficient “spring” (strain puts in 100 units of energy, and when that strain is removed, you get back maybe only 60 units—the missing 40 become heat, elevating tire temperature. This, incidentally, is the driving force behind making tires thinner and lighter. Conversely, tire engineers may add extra rubber as a means of causing a given basic tire design to operate at higher temperature.

Tread rubber is engineered specifically for its intended use. As rubber is made cooler, relative movement of its long-chain molecules slows. At a particular temperature, called Tg—the glass transition temperature—molecular motion ceases and the material has become glass-like.

Just above this temperature is a zone in which the material is becoming deformable, but the process of deforming it is strongly damped. This is the temperature of maximum grip for race tires. The more energy consumed in making the tire slip, the greater its grip.



All-weather street tires must be given a much lower Tg so they can produce useful grip in winter temperatures. Conversely, the reason race tires are wrapped in 80 degree C tire warmers for a time before use is to get their temperature far enough above Tg that the rubber has the mobility to mold itself to the pavement profile (which greatly increases the area of true contact between them).

Tread compounders would love to know race day’s temperature, wind, and other conditions. That’s why, before Dorna required all race tires to be at the track X days before use, Michelin would wait for Saturday evening’s Sunday weather forecast, then make the tires for the predicted temperature range, and fly or drive them to the track overnight. On the other hand, during Bridgestone’s time as spec tire provider (made just north of Tokyo, rather than in Clermont-Ferrand, France), they were 9000 miles away from most of the races and therefore had to develop rubber compounds with wider operating temperature ranges.

As a result, Bridgestone’s soft, medium, and hard, were more widely different in behavior than were Michelin’s soft, medium and hard, which tend to be more closely similar.

Pre-heating race tires does not eliminate possible surprises during the first three laps—cold tire crashes still happen. Rather, it makes the surprises less likely to cause crashes. The desired state is the true racing temperature distribution, which is not uniform, and varies with the bike’s location on the track. Tires temperature up through braking and corners, then cool on the straights.

To give some idea of what can happen, here are some not-very-subtle and even perhaps irrelevant examples. The usual SBR synthetic rubber (Styrene Butadiene Rubber) is made up of long molecular chains containing a distribution of two different molecules—styrene and butadiene. The styrene contains plate-like benzene rings that interfere with chain flexibility, needing higher temperature to rattle them into mobility (think of them as stegosaurus tails). This can produce the temperature zone of high internal friction that generates high grip – but at some risk. When its temperature rises a distance above its Tg, there is a steep drop in properties. This can result in narrow operating temperature range.

Polybutadiene rubber (a major component of solid rocket fuel!) is more flexible as it doesn’t contain those big clunky styrene plates that restrict rotation or the movement of one molecular chain past all its writhing neighbors. As it rises above its Tg, its properties decline more slowly than do those of SBR. The result can be grip across a wider temperature range.



Shall we blend these together somehow to get something even better? But then the usual questions arise. Can they share the same curing agent and cure temperature? Will they be compatible as their molecular chains saw against each other? Will unanticipated reactions or affinities take place, causing other kinds of degradation? Fortunately, some humans have the ability to find such matters intensely interesting. Roman emperor Marcus Aurelius wrote in the second century, Common Era, that “Those who love their ... arts exhaust themselves in working at them, unwashed and without food” (“Meditations” Book 5). A grand way to describe the all-nighters we’ve all experienced.

Loss of tensile strength leading to graining can occur at higher-than-normal temperatures. And loss of grip - Razgatlioglu, saying, “…I’m not able to enter the corner because I lose the rear and I’m not able to lean…”

Such are the complex problems riders and teams must deal with in the course of a weekend. Spectators see the action unfold, but there is no explanation for why or how their favorites have succeeded or failed. There’s a lot to this racing business, and the closer you look and study as these riders and teams have done, the more unanswered questions arise. Finding something that works today is the fascination—for the riders and for those trying to find a set-up that works with the rider’s style.

In three weeks comes Aragon, in Spain—a fresh set of unknowns.