The Le Mans 24-hour primer

It is one of Europe's biggest sporting events, but in Australia the Le Mans 24-hour sports car race doesn't generate that much interest outside the motorsport cognoscenti.

But this year, with Aussie Mark Webber the star turn in Porsche's return to the race and the World Endurance Championship, we're paying more attention.

So here's a basic rundown to help those of us not so familiar with the intricacies of this legendary event.

What:
24 Heures Du Mans. This is the 91st anniversary of the race, which starts at 3pm French time Saturday June 14 and finishes exactly 24 hours later at 3pm Sunday June 15. The car that completes the most laps wins. Three drivers share each entry.

This is the third of eight rounds in the 2014 FIA World Endurance Championship. All the other rounds are conducted over six hours. The Championship, established in 2012, is run by the Automobile Club de l'Ouest (ACO), the organiser of the Le Mans 24 Hours since its inception.

Cars contesting the race are drawn from the WEC, the European Le Mans series, the new Tudor sports car series in the USA and the Asian Le Mans series.

Who competes:
There are four classes – LMP1 and LMP2 (LMP stands for Le Mans Prototype) are pure-bred racing sports cars with enclosed wheels, while GTE Pro and GTE Am are for 'production'-based grand tourers such as the Porsche 911 RSR and Ferrari 458 Italia.

An experimental 'Garage 56' entry is also allowed, which this year is the narrow track Nissan Zeod RC. All up, 56 cars are scheduled to start the race.

Technical regulations:
The LMP1-H (Hybrid) class is where much of the technical interest lies. This is a manufacturer-based category that caters for Audi, Toyota and newcomer Porsche. Nissan has announced it will join the LMP1 action in 2015.

These cars must be hybrids and the 2014 regs target a 30 per cent fuel consumption cut over 2013 while maintaining performance equivalency.

There are a huge number of freedoms granted in LMP1, the idea being to allow the development of technologies that can eventually translate to road car use.

There is no uniform hybrid system specified, no limits on displacement or the number of cylinders of the four-stroke engines, the use of diesel or petrol, turbocharging or naturally-aspiration.

The engineers also make the call on whether to have one or two recuperation systems; the storage system is also free, so batteries, ultracapacitors and flywheels are all legal.

There are some limitations; the cars must be closed two-seaters, weigh a minimum 870kg and fit in a 4.65m long, 1.9m wide and 1.05m high box. Wheelbase is free. The giant fin over the engine hood is designed to act as a brake in an accident.

Each of the LMP1-H constructors have come up with very different solutions to the same drivetrain challenges.

The Audi R18 e-tron quattro has a 4.0-litre turbo-diesel engine at its heart driving the rear wheels. It has a KERS-type (kinetic energy recovery system) generator acting on the front axle, but an ERS exhaust recovery system – of the type adopted by Porsche – was tested but has been abandoned. Electrical power is stored and released via a mechanical flywheel battery.

The Porsche 919 has a 2.0-litre V4 (yes V4) turbo-petrol combustion engine, KERS on the front axle and an F1-style energy recovery system that harvests exhaust gases to generate additional power for the rear axle. Electricity is stored in liquid-cooled lithium-ion battery packs. The KERS system is part-time, which means the 919 is rear-wheel drive and then all-wheel drive at the touch of a button.

The Toyota TS040 combines a 3.7-litre naturally-aspirated V8 petrol engine with motor generators on both axles making the car permanent all-wheel drive. Its predecessor, the TS030, was rear-wheel drive. Energy is stored in a super-capacitor and delivers up to 354kW, boosting combined output to 736kW.

To equalise the performance of these vastly different drivetrains, fuel consumption and electrical boost per lap – measured in megajoules – is limited. The more boost the less fuel is permitted, while the frugality of diesel compared to petrol also has to be taken into account.

Audi has nominated the lowest 2MJ of hybrid capacity per lap at Le Mans, meaning the R18 gets a 4.07L fuel consumption average. The 6MJ Toyota must not exceed a 4.72L average, while the 8MJ Porsche is on 4.64L.

Outputs are monitored in real-time and the ACO calculates consumptions based on the average value of three laps, which means drivers have to be on the ball in terms of both fuel and electricity consumption. Violations are punished with time penalties.

The rest:
LMP-L (Light) is a privateer class that uses a chassis equivalent to the LMP1-H entries, but not a hybrid system. Instead, they have a lower weight limit and a larger supply of fuel to help their competitiveness against the works cars.

LMP2 uses open or closed chassis sourced from racing car manufacturers. Engines can be up to 5.0-litres and eight-cylinders if naturally-aspirated, or forced induction 3.2-litre six-cylinders. LMP2 is designed to be a privateer class.

GTE is for sports-oriented two-door, two-seat or 2+2 grand tourers that are based on fully street legal models. Maximum engine capacity is 5.5-litres naturally-aspirated or 4.0-litres forced induction.

GTE Pro is for a full crew of professional drivers, while GTE Am is for cars from the previous season with only one pro driver per team allowed.

Garage 56: The Nissan ZEOD RC is powered by a 1.5-litre three-cylinder engine putting out 300kW. It is coupled to a hybrid energy recovery and feedback system. The car is planned to compete one lap in every stint on pure electric power.

The circuit
Name: Circuit de la Sarthe
Length: 13.629km, including 9km of public roads.
Lap record: 3.19.074 (race)
Top speed: 340km/h approx. on the Mulsanne straight

Points of interest:
There are two Aussies racing at Le Mans in 2014. Mark Webber last came here in 1999 with Mercedes-AMG and flipped twice. While they were horrific incidents, he now says they were pivotal in his return to open-wheelers and an eventual Formula One career that netted nine wins.

The other Aussie is West Australian gentleman racer Stephen Wyatt, driving a GTE Am Ferrari 455 Italia.

Four Australians have won Le Mans outright – David Brabham (2009), Geoff Brabham (1993) Vern Schuppan (1983) and Bernard Rubin in 1928 (one of the 'Bentley Boys').

Toyota has contested Le Mans 15 times and never won. It has finished second four times. Promisingly however, it has won the two opening rounds of the 2014 WEC.

Audi has won Le Mans 12 times, all victories coming since 2000. It has won the last four years, but Porsche holds the record with seven (1981-7)

Porsche has a record 16 overall wins at Le Mans, but has not contested the outright (or LMP1 as it is now known) category since 1998.

300,000 spectators are expected to attend the race.

On top of the 24 hours of racing, the meeting also includes 11 hours of practice and qualifying.

The starting grid is decided by the fastest single lap from any of the qualifying sessions, the last of which occurs on Thursday night 10pm to midnight French time.

Pictures show in sequence: Audi R18 e-tron quattro, Nissan ZEOD RC, Porsche 919 Hybrid, Toyota TS040