It's business time - today is Le Mans Saturday. Our weekend started at Brands Hatch early on Friday, and the next morning sees us join spectator traffic into Circuit de la Sarthe, woven into the southern edge of Le Mans city. Of course, many are already here - a large proportion of the quarter-of-a-million fans expected to attend are dug-in at camping areas dotted about the complex's vast perimeter. We park up on a strip of grass pinched between Arnage Airport and the circuit's home straight - private jets and helicopters will ferry the slick set in and out all day at some expense, but a race ticket for the whole weekend costs from just £25.

Our base for watching the action is Club Dunlop, fronted by a small, elevated stand that lets us track cars all the way up the start/finish straight, uphill through the Dunlop Curve in front of us, then through the chicane and under the Dunlop bridge. Celebrations are in order here, for while 2013 brings the 90th anniversary of Le Mans 24, it also marks 125 years since John Boyd Dunlop patented the pneumatic tyre. Hats off to you, John. He'd have been glad to know his wares are worn by 18 of the 22 entries in LMP2, the largest class in action today.

The atmosphere mounts through the morning's support races, but a personal highlight is the 'Legends of Le Mans' parade, lead by the Bentley Speed Six that won here in 1929 and 1930. The lineup also includes the 621bhp Porsche 917K and the gorgeously petite Ferrari 166 MM Barchetta. 

On to the big race. Audi and Toyota are likely to fight over the LMP1 title (LMP as in 'Le Mans Prototype', if you were wondering) with their R18 e-tron quattro (V6 turbodiesel hybrid) and TS030 (V8 petrol hybrid) cars. The thriving LMP2 class (a more inclusive group of cost-controlled prototypes with production-derived engines) is likely to be more closely contested, while the GTE Pro and busy GTE Am classes for production-homologated cars have the most real-world interest thanks to familiar road car silhouettes from Aston Martin (Vantage V8), Ferrari (458 Italia), Chevrolet (Corvette ZR1), Porsche (911 GT3) and Dodge (Viper).

The rolling start kicks off a wave of excited applause that subsequently follows the cars around the first 8.5-mile loop. It's a real sternum-shaker. But for a lock-up or two, all the cars make it past us and up then over the hill without making contact. On the big screens we can see Allan McNish's Audi R18 dicing with Nicolas Lapierre's Toyota TS030 - there's proper argy-bargy going on between these priceless machines.

It's not long before the safety car is deployed, though, as Aston Martin Vantage 95 crashes heavily. Some time later, the car's experienced Danish driver, Allan Simonsen, is confirmed to have passed away following the accident. It's a piece of news that will be on everyone's mind for the rest of the weekend, and well beyond.

We head away from the circuit's epicentre and spend some time at one of the two chicanes than punctuate the Mulsanne Straight. Despite the slowing effect of those kinks, the cars pick up incredible pace before they leave our sight again, going from in-front-of-your-nose behemoths to distant, bobbing specks in a flash.

At close quarters, the sound from the cars really hits you, too, from the R18's sinister hiss to the whip-crack backfire between LMP2 gears. GTEs offer the most characterful barks, though: the 458's scream, the 911's boxer howl, and the harsh growl from Vantage V8 and Viper, but the Corvette's condensed thunderstorm wins the volume award.

Daylight soon turns to dusk and the headlights come on, adding a new aesthetic to the racing, while the restaurants, bars and fairground rides light up, too. But as the drivers compose themselves for the long night ahead, the punters are just loosening up. See you on the other side.