Why do F1 cars keep running out of fuel?

F1 Technology

Sebastian Vettel, Red Bull, Yas Marina, 2012When it comes to running a racing car, allowing it to run out of fuel is a failure of the most fundamental kind. Yet F1 teams run into exactly that kind of problem with surprising frequency.

Already this season we’ve seen Mark Webber run out of fuel during qualifying in China. This was the second such failure for Red Bull in six races. And in Malaysia Lewis Hamilton’s race was dominated by a pressing need to save fuel.

How are teams managing to get a seemingly simple part of going racing wrong? And why are the drivers apparently incapable of keeping an eye on their fuel gauges for themselves?

An old problem

F1 teams have long understood the value of not putting a drop more fuel in a car than is necessary. More fuel means more weight which means slower lap times. When huge sums are being spent in the pursuit of fractions of a second, no one wants to undo that work by needlessly sloshing in a few extra kilos of fuel.

That is as true today as it was 50 years ago. Lotus owner Colin Chapman was famed for his mania for saving weight. He took the practice of putting as little fuel in as possible to such lengths that when he wasn’t looking his mechanics would add a few extra litres to ensure the car reached the chequered flag.

They weren’t always successful in their covert endeavours. At Monza in 1967 Jim Clark’s Ford Cosworth DFV ran dry on the final lap after he had fought his way up from the rear of the field. Jochen Rindt and Mario Andretti were also victims of Chapman’s overzealous weight saving which sometimes extended to taking fuel out of the cars while they sat on the grid.

Working out race fuel loads

Start, Sepang, 2013Today that practice is forbidden by the rules on safety grounds, which means teams must work out how much fuel to put in their cars before they send them to the grid. Making that decision is not as simple as working out the rate of fuel consumption per lap and multiplying by the number of race laps.

Variations in climactic conditions can have a strong effect on fuel consumption. In wet conditions cars lap more slowly and therefore use less fuel. And teams will not know in advance of a race exactly how wet it’s going to be.

This gives some insight into the difficulties Mercedes had in Malaysia. As drivers headed to the grid half an hour before the start the track was so wet several of them skated off at turn four.

But in the race it dried up quickly – everyone was on slick tyres by lap nine. Not long after that the first radio messages to Hamilton urging him to save fuel were played on the team radio channel.

Whatever the conditions, the desire to put in as little fuel as possible remains pressing. Reports suggest some cars have gone to the grid this year with as much as 10% less fuel than they need to do the race flat-out. That’s a potential weight saving of 15kg on F1’s most punishing tracks for fuel consumption.

Teams deliberately under-fuel their cars because they expect their drivers won’t be able to go flat out at times during the race. For example, they may get stuck in traffic – this is especially likely for those in the midfield.

Qualifying

While this explains the incentive for under-fuelling cars in the races, it’s in qualifying sessions that we’ve seen the most extreme examples of cars being underfuelled. The ban on in-race refuelling at the end of 2009 means drivers are now running their lowest possible fuel loads in all three parts of qualifying.

To work out how little fuel needs to be in the car before the engine starts to cough, teams will often deliberately run their cars out of fuel during pre-season testing and then measure how much is left in the tank and collector.

Even so on several occasions since we’ve seen drivers run out of fuel during their qualifying runs. It happened to Lewis Hamilton in Canada in 2010 and again in Spain last year. Sebastian Vettel had the same drama at Abu Dhabi last year and, most recently, the same happened to Mark Webber in China.

Varying explanations were given for these failures, sometimes in the hope of avoiding the dreaded exclusion from qualifying (as Hamilton managed in 2010). But they shared the root cause of the team making an error in fuelling the cars during the high-pressure, time-limited modern qualifying format.

Where’s the fuel gauge?

Why can a F1 driver not tell for themselves whether their car has insufficient fuel? After all, every road car is fitted with a gauge which alerts the driver if this is the case.

The shape and construction of an F1 car’s fuel tank makes this impossible. This is due to the severe forces an F1 car experiences which causes the fuel to move around. Engineers need to control this movement – “slosh” – to keep the car’s centre of gravity low and to ensure a consistent supply of fuel to the engine.

“You can’t just put a dipstick in there,” explains F1 technology expert Craig Scarborough. “At Spa the fuel is actually at the top of the fuel tank as you crest the rise coming out of Eau Rouge!”

This video illustrates the forces at work on a fuel load in an F1 car’s tank:

http://youtu.be/PKoOeNUoNHU?t=42s

F1 fuel tanks feature a series of chambers to keep the fuel in a position where the fuel pump can collect it. This network of chambers controls the fuel ‘slosh’ during acceleration, braking and cornering. Trapdoors in the chambers allow the fuel to travel down but not back up.

This image of a 2008 BMW-Sauber F1.08 shows the fuel tank and the horizontal divides within it which help control the position of the fuel:

BMW-Sauber F1 car sliced in half

But it’s not a foolproof system. In Italy last year Jenson Button retired when one of the trapdoors became jammed in his McLaren’s fuel tank.

Degree of risk

Although they are unable to directly measure how much fuel is in their car at any given time, teams can gather readings from other sources. For example, adding fuel to the car should cause a corresponding increase in the load on the suspension.

Once the car is lapping, the team will study the rate at which fuel is being fed to the engine to calculate how much is left – and whether they’re using it too quickly. The driver has some degree of flexibility to alter the rate of fuel consumption by selecting different engine maps and by altering their driving style. Hence radio messages telling them to “lift and coast” as they approach their braking points.

Fuelling an F1 car is a delicate balance of risk versus reward. The penalty of coming to an early stop is high, but in a sport that’s fixated on performance the temptation to shave a few tenths off by under-fuelling the car is great.

There will always be those like Chapman who are more inclined to push the envelope than their rivals are. It’s telling that some teams have had their fingers burnt more than once – Red Bull and McLaren, for example – while others have avoided this kind of trouble.

Like a driver judging a risky overtaking move or weighing up whether to back off for a high-speed corner, it’s another of the high-stakes decisions at the heart of Formula One.

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94 comments on Why do F1 cars keep running out of fuel?

  1. AndrewTanner (@andrewtanner) said on 1st May 2013, 17:16

    Just another reason why I love this sport – nothing is ever straightforward.

  2. mikepaterson (@mikepaterson) said on 26th July 2013, 13:30

    Really informative article thanks Keith.

    I have a question regarding fuel use on slowdown laps.

    If an F1 car uses say 2kg fuel per lap at a particular circuit at full racing speed, what is the likely consumption in full fuel saving mode on a slowdown or in-lap?

    Cheers

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