STRAIGHT TALK – RICARDO DIVILA
Right as rain
There is more than one way to predict the weather before or during a race
nowing what the weather will do is a big
part of race preparation and strategy.
Just dry is easy; temperature and track
rubbering-up and knowing your compounds and
degradation, all fairly predictable.
Full wet, ditto, but with the added problem
of aquaplaning, when the water film between
rubber and surface can actually lift the rubber from
contact reducing your grip level enormously. The
antidote to this are sculpted tyres with grooves
to channel the water away and maintain rubber
contact. These full wet tyres are the most effective
solution for heavy rain. The grooves can evacuate
85 litres of water per second per tyre at 300km/h.
On an average track that is around 25,000 litres
of water per lap, or to put it another way, half the
volume of an 2,500,000-litre Olympic swimming
pool displaced during a grand prix per car,
and we won’t even get into the intricacies
of intermediates, designed to transition
from wet to dry conditions.
Knowing – or more accurately,
guessing using data – what the
conditions are going to be is part and
parcel of strategy, long range forecasting
giving you an idea of the possible
weather conditions for the race weekend
and of which set-up to start on.
Fine grain prediction is not that
precise yet, knowing exactly when the
rain will start and how much there will be
is still in the lap of the gods.
Just add water
Back in the day there were workarounds. For
example, for the BTCC we had observers stationed
around the surroundings of the track, all around it,
so the call to what tyre to choose on the grid was
decided by knowing what the wind-speed was
and then the phone-call from the observer upwind
to tell you whether it had started to rain. It gave
us a win at Silverstone when we started, counter-
intuitively, on wets on a dry track, but we had the
edge as we knew it was going to bucket down
halfway through the first lap.
With single seaters it was a matter of using
game strategy, with the cars on jacks on the grid,
and observing the opposition in the championship
stakes. The best strategy was to run the same
choice as your main competitors, on the reasoning
loss if the tyre choice turned out to be wrong, as
your main contenders would have to pit, just like
you, leaving both even. This used to lead to a game
of chicken right up to the five-minute board, to
avoid being caught out, waiting for the first one to
crack, wings going up and down together with the
car having two wets on one side and two drys on
the other, so as to only have to change two tyres
when the final decision was made.
Pours for thought
It worked very well most of the time, but at one
Spa race it cost us the championship when the
driver cracked, despite being briefed on the tactic,
when overtaken by a car that wasn’t in the running
for the championship. We were ahead of the other
contenders, but coming in to the pits at Spa, with
the longest pitlane of the year, it dropped us
behind. Those points sealed the championship
positions; we were second, one point behind.
Rain also brings out the skill of the driver, as
keeping the car balanced with little adhesion
highlights the driver’s sensibility and has given us
the recognised regenmeisters. I will just mention
Senna’s first lap at Donington in 1993 here.
On the pit side the rain has provided some
hilarious moments. At Pescarolo we had managed
to bring in the French weather service, having
a monitor in the pits for rain checking around
the circuit, it being notorious for having local
rain in parts of the track due to its length. When
Peugeot came to Le Mans it took over the radar
monitors from us, and the service, factories having
precedence over privateers, and to add insult to
and useful in strategy as you could come in full
chat till the yellow line then brake straight into the
pits, with no pit-limiter nonsense to lose time.
We had the last laugh, though. During the
race Peugeot engineers and weather bods were
crowding around the equipment trying to see
when the rain would come, not noticing the
mechanics jumping up and down in front of the
pits shouting to call the car in as it was already
bucketing down on the pit straight. Never depend
too much on equipment lads, use common sense,
virtuality is always beaten by real observation.
Another memorable Le Mans vignette was
when I was running the Courage 3-litre Nissan-
engined C52, backing up the works 3.5-litre R390s.
The sight of raindrops on one of the trackside
cameras on the pit monitor enabled a quick call
to ‘pit in’ while it was still dry on the pit
straight to fit wets, with a very confused
driver quizzically asking ‘Are you sure?’.
But this enabled us to leapfrog the entire
field, and most importantly the works
R390s, as they had to do a full lap on drys
on a wet track, whilst we were on wets.
I’m still chuffed about that call.
Rain of terror
The worst rain incident I recall was at
Interlagos, for the Copa Brasil back in the
’70s on a steaming hot overcast day when
there was an unusual grey, mist-like wall
on the opposite straight just at the start
of the race. Excited drivers later described
their view of the incident: a sudden tropical storm
that had every single car running into a zero
visibility monsoon that none had recognised until
slap-bang into it, and then spinning off both sides
of the track, luckily without hitting one another.
It had started raining so hard that tyres in the
pits were floating away and we could not see more
than a couple of metres ahead of us. We could
hear, though, one hesitant engine noise; a Lola 220
Cosworth, the only car that came around, driven
by Emerson Fittipaldi, slipping and sliding the
waves on slicks. Superlative car control.
Fittipaldi did something similar at Silverstone
in the 1975 British Grand Prix, when the entire field
went off at Club corner, except Emmo, who had
stopped for wet tyres the lap before, and was the
only car on the lead lap after the red flag. There
is a silverlininginevery(rain)cloud.
SEPTEMBER 2019 http://www.racecar-engineering.com 5
We started on wets on a dry track, but we had the edge as we
knew it was going to bucket down halfway through the first lap
It’s not just driver skill that’s tested in a wet race, an engineer’s
judgement needs to be spot on while luck will also play its part