Racecar Engineering – September 2019

STRAIGHT TALK – RICARDO DIVILA

Right as rain

There is more than one way to predict the weather before or during a race

K

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

that goingforthesametyrewouldminimisethe

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

injuryalsothefirsttwopits,oursfromtheyeardot

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