Three more litres

It's now been more than a week since the ACO announced that the petrol-engined LMP1 cars are to be allowed a larger fuel tank at Le Mans. At least the organiser of the most important endurance race of the year has come clean and admitted that the additional three litres of fuel that the works Toyotas, the Rebellion Lolas and the Strakka HPD will be allowed to carry is in order to better balance the performance between petrol and diesel-fuelled engines.

So, this year, the hybrid Toyota TS030 cars will be allowed to carry 76 litres, an increase of 4.1% per tank. The non-hybrid privateer entries from Rebellion and Strakka will be able to carry 83 litres, an increase of 3.75%.

In 2012, both Toyotas were only able to manage 11 laps in a stint, which means that they were using about 6 litres per lap. Audi sometimes did 12 laps on its 58 litres of diesel, although some stints were 11 as well.

Just as an aside, before diving into the arithmetic too heavily, and before anyone starts pulling the wool over your eyes about how efficient these engines are, consider this. The diesel Audi, if it used all its fuel to do 12 laps last year, would be achieving 7.8mpg and the Toyota a miserable 5.8mpg (of super-unleaded). That means if you were to drive from Calais to Le Mans, you would need to stop twice en route to refuel, even if it you topped it up to the brim before you boarded the ferry at Dover!

So while we applaud the increased emphasis on more efficient engines, we must never forget these are racing cars, designed first and foremost to optimise performance. Using the same analogy of driving your road-going Toyota TS030 Hybrid from Calais to Le Mans, you could expect to arrive in around two hours - depending on how long the queue for toll booths was!

Anyway, to return from my tangent to the matter at hand, three litres is not even enough for a lap. But it might make the difference between 11 and 12 laps for Toyota. And you get the feeling somehow, that it must make the difference. Such rule changes are not made in isolation, they are made in consultation with the entrants concerned, and we know that Toyota has been lobbying for a performance break.

So it is reasonable to expect the Toyota TS030 Hybrids to be able to manage 12 laps in a stint this year. It will mean that at the start of each stint, the cars will be 2¼kg heavier, and the pit-stops will take around a second longer.

But what I find interesting is that the ACO chose to increase the tank size of the petrol-engined cars and not decrease the size for the diesel-engined Audis. It seems pretty obvious that Toyota needed the increase to get an extra lap and it wouldn't have the same negative impact on Audi - or at least that's what Toyota must think.

From what we have seen so far this year, Audi has a much thirstier car than last year - indeed, by my reckoning, they might only be able to get 10 laps out of a tank.

The other big issue is going to be tyre usage. We have seen the Michelin tyres lasting for three stints at Le Mans in the past - indeed, Audi has been known to run a quadruple strategy in the past. And if Audi can only manage 10 laps on a tank, then a triple stint for the tyres would only be 30 laps.

Of course, there are many scenarios, but let's take just two: first, that Toyota can indeed manage two laps more than Audi on a tank of fuel, but that Audi triple stints the tyres, where Toyota only double stint them.

In this case, assuming that there are no safety car periods, then the Audis will need to make seven additional stops (each) during the race. However, if they can lap, on average, three-quarters of a second faster than the Toyota, then they should (according to my projection software) be ahead at the end of twenty-four hours.

Second, let's suppose that Toyota's fuel advantage is only one lap, but that both teams can triple stint the tyres. This will enable Toyota to complete an extra lap over 24 hours, but it will have to maintain an average lap time within half a second of Audi in order to win the race.

In a nutshell, it is all finely balanced. The underlying theme is that Audi has the quicker car, but it will have to stop for fuel more often. The projections above both assume the ‘perfect race’ though - i.e. no fumbles on track or in the pits, no safety cars and no rain.

These days, that is not such a wild assumption, but bear in mind that each of the works hybrids will need to make more than thirty pit stops and over a thousand overtaking manoeuvres during the race, so achieving perfection is a very tall order indeed.