Huff's new endurance challenge

America is known for some famous endurance races: Petit Le Mans, the Sebring 12 Hours and the Daytona 24 Hours are events that resonate with motorsport fans all over the world. But you'll likely get blank stares back if you mention the US's longest endurance race: the Thunderhill 25 Hours.

Never heard of it? Neither had we. But American endurance racing's best-kept secret has been running for a decade, on a circuit that last year celebrated its 20th anniversary.

Think of Britcar's Silverstone 24 Hours, but on three miles of undulating purpose-built track in the North Western part of California's Great Central Valley...

Just like Britain's only round-the-clock race, Thunderhill is an amateur event at heart. Scores of 'run-what-you-brung' Mazda MX5 variants, BMW saloons, SEAT Cupras, Honda tin-tops and one-off specials make up the bulk of the grid - which even includes a NASCAR truck! But the pointy end is all about hairy GT cars (and modified Radical and CN prototypes).

As the event has become more established, so the quality of the entry has grown. Members of successful GT squad Flying Lizard are here, running a Porsche GT3 Cup car for Award Motorsports; Honda Performance Development too; factory-blessed entries from Mazda and Lexus; plus GMG (Audi R8) and Rotek Racing (Audi TT RS) with customer support.

The driving strength includes a smattering of racers known outside the US (Al Unser Jr, driving a V8-powered Wolf CN prototype with his son Al Unser III and SPEED Euro Series champion Ivan Bellarosa, and Grand-Am ace Memo Gidley, piloting the 'Lizards' Porsche), plus drivers known well within it.

As the event has gained prestige, the quality of the entry has grown

There's nowhere near the quality seen at the blue-riband enduros, but Thunderhill's 'clubbie' is gaining its own momentum, even if the 60-car entry is slightly down on previous editions.

Rotek, the fledgling team owned by bit-part touring car racer Robb Holland and his friend Roland Pritzker, is the reason AUTOSPORT has a chance to witness the 25 Hours first-hand. The squad led 2012's edition in the early stages before a transmission problem put its VLN-spec TT RS out of the race.

This time, after several class wins in the 2013 VLN series on the Nurburgring Nordschleife, the team is back to avenge that defeat, drafting in 2012 World Touring Car champion Rob Huff to lead the charge.

"I'd never heard of this race before," says Huff, who first met Holland when the American tested Tony Gilham's S2000 BTCC Honda Civic at Snetterton in 2012.

"It's a bit like the Bathurst 12 Hours. I'd never heard of that before last year [when he partnered fellow Brit James Winslow to eighth in a Peter Conroy Audi R8 LMS]. But endurance racing is getting bigger, and the more high-profile drivers and teams that enter, the more publicity it gets. All of them start as local clubbies, just like this one."

Huff is first in the car during Thursday testing, getting a feel for the track and refining the set-up. His first impressions of Thunderhill are positive: "It's a good circuit; fairly basic but fun because it's fast and there are two or three blind bends. It's only the second American track I've driven, after Sonoma; I'm impressed.

"The average speed is high [around 100mph] and there's not too much stop-start, so you can get your flow on."

Car dialled in, Huff's co-drivers take turns to get up to speed. Former World Challenge (think the US version of the BTCC) champion Jeff Altenburg and fellow tin-top racer Kevin Gleason (son of 1960s Formula Ford race winner and Le Mans racer Chris) both get a go, but the Audi runs into a terminal ECU problem before team owners Pritzker and Holland get a chance to hop in the hot seat.

Huff on more familiar territory in the WTCC

Blind Dogs Smokin' bass guitar player Pritzker is particularly unimpressed, having geed himself up with strong coffee in readiness.

The car is parked for most of Friday too, but Roland finally gets his go when the team (having spent the best part of 12 hours failing to make an R8 unit work) finds a replacement ECU from a TT RS road car and has the Rotek racer purring like a cat again - once a technician in the UK has cracked the car's immobiliser code!

Qualifying begins as darkness descends on a bitterly cold circuit. Huff puts the Audi ninth on the grid, behind three GT3 Porsches and five prototypes.

He's slated to start the race too. "It's not going to be a race, it's going to be testing for 25 hours because the closing speed with some of the cars is horrific," he warns. "Sixty other cars out there spells danger!"

Fortunately, the Rotek Audi keeps largely out of trouble through the race. The car's fuel economy is its biggest strength and a strong opening stint from Huff has Rotek briefly in the lead before its first pitstop. The team flits around the top six for the first quarter, and then takes a commanding lead in the early hours of Sunday morning as its main rivals wilt.

The Radical V8-powered Unser Wolf (in which 'Little Al' sets fastest lap) is the hare to Rotek's tortoise, and looks a real threat to catch the Audi before the end, until it blows its engine spectacularly and gets hit by another car, putting it out with six hours to run.

That leaves Rotek clear to win by 28 laps after a near-faultless run (save for a couple of minor incidents and two stop-go penalties for pitting under the safety car).

It's the team's maiden Thunderhill victory, at the fourth time of asking, and the first for Audi.

"It's amazing really," reflects Huff, having brought the car home. "To win a race like this is a bit special. But to win it by nearly 30 laps; we couldn't have asked for more."