Senna's last title-winning F1 car: Why McLaren 'had to start again'

“[But] on the MP4/6, the two surfaces that run from the front to the back of the monocoque are on a curve, they don’t actually change direction with an angle – it’s a flowing surface.

“We wanted to reduce the number of changes of angles that the [carbon-]fibres had to go around, to improve torsional stiffness.”

Not that this initially appeased Senna or his team-mate Gerhard Berger much.

“They thought the power wasn’t enough,” recalls Jeffreys. “And Honda said ‘We’re just not running it at full power, we would prefer the reliability.’

“That was it, it wasn’t powerful enough, and it was heavy. So there was concern, even though we’d won the first four races.”

Despite Senna making a clean sweep of 1991’s opening quartet, all at Woking could see the storm on the horizon.

“The Williams was a far better car,” says Robinson. “But they had a major gearbox problem.

“They didn’t know what it was. They were smashing gears. It turned out they were selecting two gears at the same time, because of their transverse box…”

Senna would go out of ‘91’s fifth round at Canada with electrical issues, the first of five races without a victory.

Before that race he led the championship with 40 points, his closest challenger being Ferrari’s Alain Prost on 11 points, with Mansell on six points.

After the five-race lean spell, he had 51 points to Mansell’s 43, the Brit taking a hat-trick of victories in the meantime.

Among reliability and weight issues, Senna’s McLaren’s colleagues remember he would test their nerves with some daredevil lack-of-economy runs too.

“We knew we had a fight on our hands,” remembers Jeffreys. “A number of things started to creep in – we also had problems with fuel reading, in getting an accurate fuel measurement.”

“He would use more fuel than he was allowed to use early on in the race and say, ‘Well, the race is at the beginning. At the end, I can back off and save it,’” says Robinson.

“So he would go very negative on the meter, which would have us all on the pitwall screaming at him, and he’d just go: ‘Don’t worry, I can get it back – but in two races [Silverstone and Hockenheim] he didn’t, and ran out!”

Things started to come back together in Hungary when Senna was once more on top of the rostrum – but it wasn’t easy getting there.

“The car wasn’t brilliant,” says Robinson. “And one thing I had not been used to – Henri Durand [who moved to McLaren from Ferrari for 1991], who had done the aero on it, was very much: ‘I’ve designed this car, this car is perfect.’

“And I’m going: ‘No, we need to be developing the car. We need to find two-tenths a weekend.’ And he was adamant: ‘No, no, this is the car. We can’t change anything. That’s the best car I’ve done.’

“There was a bit of a fight within the team and all of us about trying to improve the car, because you’ve got Ayrton ringing you up, banging on each weekend.

“[In contrast] Honda would do that [improve their product]. They would come every weekend and say: ‘Mr Senna, we have found 10 horsepower’, or whatever it was. He’d demand to see the graphs and ask where the power was on the torque curve.

“Martin [Whitmarsh] had wanted Henri because he liked Ferrari’s front wing,” says Jeffreys. “But it turned out that was done by someone else at Ferrari!”

The eventually-redesigned MP4/6 which Senna took to victory in Hungary managed to combine its more powerful engine (now 780bhp) with a new, lightweight monocoque. Jeffreys explains the process.

“The only way you can really do it is to look at everything,” he says. “And if you can take 2 or 3% off everything, then that’s quite a lot.

“It’s very difficult to find big chunks, where you can say ‘Oh, that could be half the size of that.’

“And you have to make things more efficient as well – which affects your thinking in terms of the design.

“When were were looking at the dampers, it struck me that the line where nose cone joins to the rest of the body cuts across the Marlboro chevron, meaning George [Langhorn] in the paint shop had to paint two little triangles of Marlboro red over the nose.

“It’s one of the qualities of McLaren, the ability to develop the car”

“So we decided to split the join of the bodywork so it follows the line of the [cigarette design] chevron.

“It’s just how your brain works when you’re looking for the efficiency of everything.”

The changes made the difference – in the six races from Hungary to Japan, Senna would score two wins and three second places to clinch the championship with a race in hand before the season close.

Managing to dig deep when he needed it most – with the help of a brilliant team – it’s perhaps Senna’s greatest title triumph.

“We produced more ‘6’s than we would normally have done in a season,” says Jeffreys.

“We had to keep finding new ways to be competitive. We were aware we had to shed weight and increase power on both sides.”

“I think it’s one of the qualities of McLaren, the ability to develop the car,” says Robinson.

“That’s McLaren’s depth. That was Ron, if people got a bit sidelined, he’d put them on different projects. Other teams would have let go of them. But you could bring them back in if needed.”

As ever though, Senna was a driving force.

“I’d worked with Nelson Piquet at Williams, so was used to the technical, methodical approach, but with Ayrton it was an extreme level,” remembers Robinson.

“The thing is that confidence circle goes around. If you’ve not got confidence in your driver and your driver hasn’t got confidence in you as an engineer or in your team or whatever, then the snowball doesn’t roll.

“The difference with Ayrton was that driving the car was 1% of his effort. His mental capacity was what gave him the difference. He knew what was going on the whole time.”