Some like it Hot
Once again, I’m confused!? I love SPEEDS coverage of FIM World Superbike racing and set aside time to crack open an icy cold Red Bull and turn the TV up load! Announcer, Jonathan Green and co-caster former World Endurance Champion and WSBK competitor Steve Martin, get going on about the hotter weather and track temperature means most riders opted for the softer tire…What?Pirelli Tire Testing Manager Salvatore Pennisi explains, “Please consider first that I’m not a chemical engineer, and this a very basic explanation. The grip on a standard type of asphalt is in an inverse proportion to the tires temperature.” In other words, the opposite side if the equation “Yes.”
“So, at low asphalt temperature there is more grip and aggressivity—mechanical type grip because of contrasting tempretures— while at high temperatures it’s the contrary. In addition to that the chemical integration of the affinity between the rubber polymer and the asphalt components is changing. This is the effect the migration of the oils inside the asphalt and of the dilatation of the profiles of the tires grains at a microscopic wavelength that is an important component of grip.”
Shouldn’t that be the other way around…track temperatures go up, so shouldn’t the tire durometer?
Pennisi continues “At high temperatures you need a softer compound to counterbalance the lower asphalt grip while at lower asphalt’s temperature you need a harder compound to resist to the more aggressivity of the asphalt, counting on the more grip of the asphalt itself.”
During further discussion my I’ve become less confused by the fact that a soft tires works when it’s hot because a soft compound has a high elasticity—due to both the mixing process and the time and temperature it spends in vulcanization process. This elasticity allows the rubber compound to squirming movement on the tires carcass which creates heat the tires to warm-up quickly. This characteristically is what makes this softer Pirelli tire better right from the start of the race.
As practice comes to a close, teams develop their tire choice hypothesis for that meeting. Another fact that must be considered is, that when a softer tires level of elasticity is met with cold temperatures, the difference in the rigidity of rubber and of the contact patch can become too great, and now that flexible foothold on the pavement surface causes cold tears the tire to shreds.
The other side of the flipping coin toss is the choice has to be decided before the start of the race—which compound to “stick” and manage for race distance. Fast start, good grip gamble from the word go— that is…will it go the distance before tire degradation leaves rider searching for grip; praying he passes the checked flag, before a rider who choose to start on a harder Pirelli whistles past out of his draft.
A harder compounds lower elasticity means it needs heat for the carcass and compound to flex and adapt better to the road surface variables. And a derivative of lower elasticity— harder compound choice that may last longer but the other side of that coin is possibility of rapid wear caused by wheel-spin?
Then there’s race two! And what if it rains? That’s another story…
Of course, the use of tire warmers— on racing compounds—combined with proper suspension set up will provide the maximum durability and performance no matter what the tire choice.
Pirelli’s has been the soul supplier of tires to FIM WSBK since 2004. The experience gained in this kind of heated competition is turned into the latest compounds developed for each race venue. Temperatures ranges remain—SC0 from 47/ 77°F, SC1 68/114°F, SC2, 47/122°F, SC3 operate in the same temperature range as the SC2 47/122°F, are used on more aggressive surfaces. While—SC0 SC1, SC2…etc—stay the same the actual compound constantly changes to improve grip, and durability, for that particular weekends racing.
Why I can hardly wait for the next round of World Superbike. With all alternatives programming on TV, motorbike racing is still my first choice.