Image caption A quarter of a million fans travel to the Le Mans race every year

This weekend, on the stroke of 1500 local time, 55 high-powered racing cars will roar off the starting grid to begin perhaps the most celebrated and most demanding motor race in the world.

They will joust with one another at high speeds through a night and a day, on bumpy public roads which normally carry the rather more mundane traffic of commuters' cars and delivery vans.

This is the Le Mans 24 hours, an automotive marathon which takes place every year on the outskirts of the city of Le Mans, in north-west France.

First held in 1923, it was designed as an endurance test, enabling manufacturers to prove the reliability of their latest models during an era when breakdowns were commonplace.

But these days, most of the four-wheeled missiles which hurtle down the fabled Mulsanne straight at more than 200mph bear no more than a superficial resemblance to the kind of cars you or I might hope to buy.

And while the race has a special place in motor racing folklore, attracting some 250,000 spectators every year, even the dullest, most monotonous Formula 1 Grand Prix tends to attract more media attention.

So why do car manufacturers continue to pour money and resources into trying to win this gruelling event, which rewards endurance and guile far more than outright speed?

Racing thoroughbreds

This year, the fight for the winner's laurels is likely to be between Peugeot, Audi and Aston Martin. Three very different manufacturers, with subtly different motives.

Sportscar firm Aston Martin has a long history here. It won the race in 1959 and the appeal of its brand draws heavily on the successes and heroic failures of the past.

Image caption Peugeot's winning car from 2009 is an attraction at this year's event

For Aston then, Le Mans seems like a perfect fit. It is a high-performance brand, which markets cars for their sporting qualities, and by racing here, it can draw attention to its sporting heritage.

"Le Mans is a race for thoroughbred sportscars," says Aston Martin chairman David Richards.

"A combination of speed and reliability are crucial, traits that are ultimately key to the success of our road car products."

But Aston Martin's approach isn't risk-free. For all the glamour associated with its brand - which includes being the supplier of choice to James Bond - it remains a small company.

It simply doesn't have the financial resources to compete on an equal level with two of the biggest names in the car business: Peugeot and VW-Audi.

Yet because it trades on its sporting prestige, it cannot afford to be beaten too often by a brand such as Peugeot, best known for building mass market family cars.

Car next door

Peugeot, meanwhile, is aware its brand lacks glamour. It competes in motorsport around the world to add lustre to its car-next-door image.

The company turned its back on Formula 1 after an unsuccessful campaign in the mid 1990s. Since then, it has competed successfully in touring cars and rallying.

But it has a special relationship with Le Mans, a race which has huge resonance in France. It won in 1992 and 1993 before claiming another victory last year.

At this race, Peugeot presents itself as, to all intents and purposes, a national team. Its efforts here are designed, above all, to boost its standing in its home market.

Image caption Audi says motorsport brings it credibiilty

Audi, by contrast, is looking far away from its home market when it competes at Le Mans.

The German marque, an upmarket division of Europe's biggest carmaker, Volkswagen, has spent the past decade building up sales in North America.

During that period, Audi has won the 24 Hours nine times.

It has also competed regularly in the American Le Mans Series - a championship for cars eligible to compete at Le Mans.

The company believes that this has reaped huge benefits, raising the public profile of the Audi brand, and giving it a much zestier, more youthful image.

"The return on investment is how you improve the image of your brand," says Audi's head of motorsport, Dr Wolfgang Ullrich.

"Sportiness is a key factor in the branding of Audi - and Audi is now seen as faster and sportier every year. So our investment is working."

Advanced engines

But competing at Le Mans is not just about branding. It is also about developing new technologies.

Unlike most forms of motorsport, Le Mans style sportscar racing gives competitors a great deal of technical freedom. The rules are designed to encourage different kinds of engines and different kinds of fuels.

Both Audi and Peugeot have taken advantage of this, using Le Mans as a test bed for highly advanced turbodiesel engines.

The technology developed on the racetrack is already being used by both companies in the cars they make for the public.

Image caption Formula 1 racing can be a costly affair

"People used to say diesel is slow, it's loud, it's smelly," says Dr Ullrich.

"They don't say that any more. It is important to race in a way that lets you run and prove new technologies, to improve performance, efficiency and fuel consumption.

"So where better to do it than at the toughest race in the world?"

For both Peugeot and Audi, racing at Le Mans forms part of a carefully thought out motorsport strategy.

Both compete in other championships, where it's fair to say the cars look much more like the models you might find in your local dealership.

But those populist series do not offer the technical freedom or the gruelling challenges of the Le Mans 24 hours.

But this doesn't matter - because both manufacturers believe that competing at Le Mans is worth the extra expense.

To put things into perspective, in recent years the cost of running a mid-grid team in Formula 1 has been more than $200m.

"For a budget like that," says Dr Ullrich, "I could do touring cars, Le Mans and the American Le Mans Series for several years."