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Twenty-Four Hours in the Balance!

Cars will begin to assemble this week in the Le Mans paddock for the official Test Day on Sunday, ahead of next month’s 24 hour race. This year, the 24 hours of Le Mans is being more eagerly anticipated than ever before, with works LMP1 entries from Audi, Toyota and Porsche – the first time there has been more than a two-way battle for overall honours for more than a decade.


There has been a great deal spoken and written about the new-for-2014 regulations and I am sure that dailysportscar’s readers do not need to go over all that ground again. There have, of course, also been two six hour races already held to these regulations, at Silverstone and Spa-Francorchamps, which have provided some indications about how well those regulations have been structured, and – perhaps more importantly – how the 24 hours of Le Mans might go.

The new regulations – in the spirit of the age in which we now live – speak of efficiency, energy-use, hybrid technology and so on. Indeed, manufacturers are compelled to enter cars in the so-called LMP1-H category, required to use hybrid drivetrains that utilise electric power that theoretically could deliver up to 8 mega joules (MJ) per lap of the 13.6km Le Mans circuit. Despite hopes to the contrary, none of the three manufacturers concerned has gone for the full 8MJ option, with Toyota and Porsche both choosing the 6MJ sub-category, and Audi just 2MJ.

At Spa-Francorchamps, Bernard Niclot of the FIA made a presentation to the assembled media, explaining how the regulations work. Keen readers will have already downloaded the technical regulations from the FIA website and will know that the key element is in Appendix B. This specifies the instantaneous fuel usage permitted (in kilogrammes per hour) and the average energy consumption allowed over a three lap average (in MJ per lap). The different fuel capacities for each configuration of LMP1-H car are also described. The problem for most members of the public is that the amount of energy provided by a litre of fuel (diesel and petrol are different of course) and the density (i.e. the weight of a litre) is not so easy to establish. Indeed, it is dependent on temperature and atmospheric pressure, so it is actually variable.

The FIA presentation provides some assumptions for the key parameters though, and shows how the regulations have been structured in order to (a) make more fuel available to those teams that use less powerful hybrid systems, to enable the internal combustion part of the power unit to give more energy and (b) to equalise diesel and petrol powered teams.

The key numbers (issued by the FIA) are laid out below:

Toyota/Porsche (petrol) Audi (diesel)
Fuel tank size 2013 (litres) 76.0 58.0
Fuel tank size 2014 (litres) 68.3 54.3
Tank reduction 10.1% 6.4%
Permitted MJ per lap 139.5 138.7
Equivalent fuel per lap (litres) 4.79 3.95

[sws_divider_small_padding]Note that both Toyota and Porsche are running in the “up to 6MJ per lap” category, so are running to exactly the same parameters, even though Porsche uses a turbo-charged, four-cylinder engine and Toyota uses a normally-aspirated 8-cylinder.

Unlike last year, there is no constraint on the amount of air that the engine can take in: “air is free,” said ACO Technical Director Vincent Beaumesnil, famously, and boost pressure is also free. It does not take a genius to work out that the Toyotas and Porsches should therefore be comfortably able to complete 14 laps per stint, whereas Audi will only be able to complete 13 laps. Somewhat bizarrely, the official ACO presentation states that Toyota and Porsche’s range will be 13.9 laps, but this assumes that there would be 1.7 litres of unusable fuel left in the lines, which seems a little extravagant to me.


There is nothing to stop cars using less fuel than this of course: indeed since the whole point of the regulations is energy efficiency, if they go further than this, then the aims of the ACO will have been achieved and no rules will have been broken. The problem comes if the three-lap average fuel use is greater than these rates. Then we might see cars coasting through the Porsche curves (or maybe the Ford chicane), in an effort to get their average back on track before the end of any three lap period. Don’t laugh: this has already happened this year.

In 2013, Audi’s victorious R18 (hybrid) was using around 5 litres per lap, so the requirement for this year is to improve fuel consumption by more than 20% (not quite the 30% advertised by the ACO).


However, this is not the whole story. In addition to the average energy use per lap, the hybrid-powered cars are also constrained by a limit on ‘instantaneous’ fuel use. This is measured by the famous Gill fuel sensor – two of which are mounted on board each car. This limits Toyota and Porsche to a maximum rate of fuel consumption (not energy consumption) of 89.5kg per hour. For Audi, the maximum diesel fuel consumption is 80.2kg per hour. To be clear, this is not an average rate, it is an absolute limit: rather like the pit lane speed limit, it may not be exceeded at any time. Just because you come into the pit lane at walking pace, you may not then exit the pits at 100km per hour!

Just to put this into real world numbers, though, the consumption limit, when translated into miles per gallon (and with apologies to European readers) equates to a requirement not to consume fuel at more than 5.7mpg for petrol, or 6.8mpg for diesel – hardly an economy drive!

Importantly, though, this limit does not constrain the amount of electric energy that is deployed. Hence Toyota, with its hugely powerful super-capacitor, can release maximum power to provide nearly 1000bhp, if its publicity is to be believed, without exceeding the fuel consumption limit; whereas Porsche, if it would increase the boost to its V4 for extra power, would immediately be in trouble for using too much fuel. It is worth pointing out though, that the ‘instantaneous limit’ is nearly 50% greater than the three lap average, but it would be possible for a reckless driver to exceed, nevertheless!

What is unclear (to me and to many others) though, is why this is a meter and not a limiter. Even though it has not been necessary for any penalties in the first two races, it would make everyone’s life so much simpler. I am told that it is partly to do with the fact that fuel is less dense when it is warmer, so the volume of fuel being consumed is variable, even when the weight is fixed.

The FIA would certainly seem to have got its sums right though, if the races at Silverstone and Spa are anything to go by. The amazing thing is that all three manufacturers seem so close, despite using such different technologies. However, it is worth scratching the surface of this just a little bit, in order to see who might end up at the end of the race with the strongest contender.


Here are a few random results of the various analyses that I have done from Silverstone and Spa: I present them without the full justification, but trust me, I have done the sums and believe that they are all true!

First, it seems that Porsche’s lithium-ion battery packs may not be able to get a full charge at the end of twenty-four hours racing. Toyota’s super-capacitor may not degrade in the same way, but it does leak charge, meaning that it will possibly not be fully charged when it arrives at Tertre Rouge (unless the drivers charge the super-capacitor by simply lifting off the throttle through the Dunlop esses). Also, the Toyota is fully dependent on the hybrid system working in order for the brakes to work adequately. Audi’s less potent hybrid system is far less critical to its overall performance, even if they will be stopping for fuel more often. Toyota has sharpened up its pit stop procedures such that they can change all four wheels more quickly even than Joest at Audi.

I have done some estimates (you wouldn’t have expected otherwise) – I am expecting the following average lap times at Le Mans during the 24 hours:

Audi: 3m 29.1s
Toyota: 3m 28.1s
Porsche: 3m 28.5s

Using the same projection method, I expect the best time from the Test Day to be around 3m 24.0s for a single lap. If I’m wrong on that – and we’ll know by the end of eight hours of track time on Sunday evening – then I’ll probably need to adjust the average lap times accordingly.

But, given that Toyota and Porsche will be going 14 laps on a tank of fuel, then they could complete the race on 28 stops, and if there are no lengthy delays for weather or safety-related issues, the arithmetic suggests they could complete 398 laps. In 2010, André Lotterer, Marcel Fässler and Benoît Tréluyer completed 396 to break the distance record. At record speed, they were averaging 6.2 litres of diesel per lap – around 50% more than the restriction imposed by this year’s regulation.

It remains to be seen whether the distance record will be broken this year – but it is certainly within reach, if circumstances allow it!

Paul Truswell