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Formula One heads to the hills
of the Ardennes for the Belgian Grand Prix, held at Spa Francorchamps, a
location where Bridgestone’s range of wet weather tyres stand a strong
chance of coming into play.
 Over the years there have been many wet races at Spa, with the local climate
creating a breeding ground for precipitation, and with the longest circuit
on the F1 calendar, it’s quite possible to have rain at one end of the track
and blue skies at the other.
When the track does get wet, Bridgestone has two types of wet weather tyre,
the ‘wet’ and the ‘extreme wet’ Bridgestone Potenza. These two tyres look
very different from each other, with the extreme tyre featuring deeper
grooves and having a greater resemblance to the tread patterns of road
tyres.
Whilst the wet tyre is capable of displacing in the region of 34 litres per
second per car, the extreme wet can displace almost double this at 61 litres
per second, with these figures dependant on the speed travelled and amount
of water on the track. It’s not just the tread on the tyre which differs
from the dry tyre. A wet track means a cooler track, so the operating
temperature of the wet tyres is much lower. Whilst a dry tyre works in an
operating range of 80-110 degrees Celsius, the wet tyre operating range is
approximately 65 degrees Celsius.
“The compounds for our wet tyres are completely different from the compounds
we use for dry tyres,” explains Hirohide Hamashima, Director of Bridgestone
Motorsport Tyre Development.
“Wet tyres need to operate in a different working range. The wet tyre is
designed to work when there is water present, and this means the compound is
different. A compound made for dry weather use would not work to the best of
its performance capabilities in the wet. An example of why the compounds are
different can be seen by looking at tank tape. This works very well when
used on a dry surface, but is much less effective if you try to stick it to
a wet surface.
“The second area that is different is that there is a tread pattern on our
wet tyres. This is designed by combining both human knowledge and computer
simulation. Our hydro simulation supercomputer helps a lot here as there are
many types of wet tyre tread pattern. If we didn’t have our hydro
simulations we couldn’t evaluate all of them, as it would take too long.”
Once a wet tyre has been designed and been through computer simulations, the
difficult thing is being able to test these tyres in the type of conditions
they would encounter in a race.
“Wet tyres are to my mind the most difficult ones to develop,” says Kees van
de Grint, Bridgestone Motorsport Head of Track Engineering Operations. “One
of the factors making development difficult is being able to test in real
life conditions.
“With a dry tyre, if you want to test it in hot conditions you can find a
hot place in the world, or if you want to test it in cooler conditions you
can also find an appropriate place, but to find a circuit where nature will
simulate on demand the conditions of a wet track is impossible.
“You can artificially wet the track with sprinklers or water lorries, but
the track temperature will not correlate to the conditions as the outside
temperature would be unrealistic for rain conditions, and this makes
developing the compound’s working range difficult.”
However, by using the hydro simulation programme, Bridgestone is able to
evaluate a vast number of possible wet tyre variations and narrow the
options down dramatically. This in turn means that, although getting
consistent on track wet conditions for wet tyre comparisons is difficult,
when genuine wet weather testing is possible, there is a greater chance of
testing these fewer types of tyre specifications within a shorter time frame
and therefore possibly in the same weather conditions. This allows
Bridgestone to gather very effective wet weather comparison data.
Over the course of a race however, weather conditions are often variable and
when to use the correct tyre can and will make the difference between being
a hero, or going to zero.
“Designing and testing the wet tyres is one factor, but in wet race
conditions making the correct call on when to use which tyre is crucial,”
confirms van de Grint.
“For the teams and drivers it’s all about finding the sweet spot of matching
the tyre choice to the conditions, with the conditions being a consistently
moving target. Making the right call can mean a race winning performance.
“When a driver is in the optimum situation of the tyre being perfectly
matched to the conditions, he will look very impressive on track. When he is
just inside the window of using the correct tyre he will be going well.
However, when he is just outside the window of using the correct tyre, he
will be nowhere.”
A wet race is an instance where team strategists really earn their money.
“Just when you think you have made the correct choice, the window changes
because there’s either more rain or the rain stops. This means the whole
situation changes again and the driver who was quick is suddenly not quick
anymore, or a driver who was slow is suddenly fast.”
As if that wasn’t difficult enough, tracks react differently when rain is
added. “You also have to keep in consideration the type of tarmac, the
drainage of the circuit, how quickly it dries out and how susceptible it is
to standing water.”
In addition to all the theory, testing and experience, the driver plays a
very important role when it gets wet.
“I remember one race where, from a theoretical point of view, the drivers
should have been on the extreme wet tyres, but the drainage of the circuit
was that good that one driver felt that the wet tyre could cope,” explains
van de Grint. “When that driver left the pits I was shaking my head,
thinking ‘there goes a brave man’. However he was absolutely correct and was
flying in the conditions.”
It’s not just making the correct tyre choice for the conditions, but also
making the correct choice of tyre pressure within the range that Bridgestone
gives to teams.
“Finding the optimum tyre pressures in the wet is also a very difficult
story as these also depend on the conditions,” says van de Grint. “In simple
terms you need a bit more pressure to keep the grooves open for good
drainage if there’s a lot of water, but if there is less water then this
will overheat the tyre.”
All in all, wet tyre performance in race conditions is far from an exact
science, but something which has provided Formula One with some very
exciting races over the years.
“To make the correct decision in the wet relies on experience and frankly a
bit of luck,” says van de Grint. ”Sometimes two plus two does not equal four
and you have to improvise!” |
