WHEN THE mercury is touching 42 degrees centigrade it is a hot day no matter where you are, but perhaps it feels even more so at Infineon racetrack in Sonoma, northern California. Here, it is fry-your-breakfast-on-the-bonnet-of-your-car hot. For Bathgate-born Dario Franchitti, the Nascar rookie who is halfway through another hard day not at the office, it is even hotter. At the wheel of his 5.8 litre Dodge the temperature is 65c, the hottest he's ever known it.

Since leaving IndyCar as champion after an 11-year stint - which included walking away from two spectacular somersaulting car crashes, described with typical West Lothian deadpan humour as "not good" - his $30 million move from open wheel racing to stock cars has been a frustrating one. In the nine Sprint cups he's started, his highest finish has been 22nd. It's fair to say that luck has not been on his side. He missed five races after breaking an ankle at Talladega, was hampered by an accident in Pocono, which was followed by an engine failure in Michigan, turning an otherwise good race into a last place.

Despite his shaky start to life in Nascar, Franchitti has plenty to be upbeat about. He has reached his childhood dream of being a racing driver and has a Hollywood actor wife, Ashley Judd. But it has not happened without hard grind, and racing as fast as a car can be pushed in roasting heat with a symphony of a thousand chainsaws in your eardrums is not as glamorous as it may appear.

Taking a well-earned break between practice and qualifying in the relative sanctuary of an air-conditioned team bus, Franchitti talks of his decision to leave IndyCar.

"I'd never felt it before but about this time last year I wasn't sure I wanted to do it much past the end of the year. I'd won the Indianapolis which was a big goal for me. At the time I was in contention for the championship and I thought this is probably the last season I want to do in IndyCars. I was lucky that I left a winner. I won my last race to win the championship, which was mega. Then I got the offer from Nascar and that was it."

Nascar is the No 1 spectator sport in the US, holding 17 of the top 20 highest attended US sporting events. Track attendances can be as high as 200,000 and it is the No 2-rated regular season sport on television. Each race is watched by an average of 7.2 million fans across the US and races are broadcast in more than 150 countries and in more than 30 languages.

As expected, the 35-year-old Franchitti holds himself to the highest of standards and is determined to crack the tough nut that is Nascar.

"IndyCar is like driving a souped-up Ferrari, Nascar is heavier with a lot less grip. It's like driving an SUV."

Last year with IndyCar he qualified in pole position on this Sonoma track. "Today it's like, oh my god it's a different track. There's just no grip, it's like driving on ice. An Indycar does really what you want it to, or a least you can try and coax it to do what you want it to do, the levels of grip are higher but it breaks away faster when it does go. In Nascar the car starts to slide earlier but there's a bit more leeway for correction. You can catch it a bit more but there comes a point when it does go, that being so heavy there's no getting it back."

When asked why they don't lower the cars' suspension, regulations is the reply, it is a spectator sport after all.

Why America, though? Why is Franchitti not racing with compatriot David Coulthard behind the wheel of a Formula One car?

"As a kid it was one of my dreams to race Formula One," says Franchitti, who tested with Formula One teams, "but I think the F1 dream is always to win, and with the teams I was talking to that was never going to be an option."

Although in Whitburn no more, his Scottish ties are still strong. He obviously misses his family and the food. "All the stuff that's bad for you," he says. He can't do without his supplies of Irn Bru either, specially sent to him by the rep. "It's great after a race," he said, but he had to limit himself as stocks were low.

As for Hollywood, Franchitti is too busy with racing and testing to get too caught up in the glamour and hype, only going to the premieres of films Judd's worked on.

They live on a farm in Tennessee and don't get involved in the LA lifestyle, which is perhaps why he has stayed so down to earth and unaffected by the spoils of success. If you met him in a pub in West Lothian you could find yourself chatting about football - he's a passionate Celtic fan - without realising that he leads a jet-set life, collects Ferraris and flies his helicopter on his days off.

In the days leading up to a Nascar race a vast base camp city of mobile homes is set up by fans behind the track. Such is their loyalty that they travel thousands of miles to attend and show their allegiance by flying flags of favourite teams and drivers.

Randy Axmer sits in the shade but still in the sweltering heat, knocking back a few beers and tries to put his finger on the mass appeal of Nascar. "Because it's f****** awesome man!"

According to Axmer, the best of the best come here, the competition level is intense and the cash draws the better, experienced drivers. Some fans follow the teams, some the drivers. But some will desert a driver if he switches from say Ford to Chevy, even if they have been supporting a driver for 10 years.

The "Talladega Nights" Southern backwoods stereotype is perhaps a little unkind to the sport. Put into context, spending a few days in the sun drinking beer with family and friends, watching your teams rattle round the track at high speed doesn't look so bad really. Not compared to a Scottish Cup game in early January anyway.

When Franchitti's PR looms ominously, transmitting telepathic "round up the interview now" signals, he is handed a water bottle that's tinged orange - "they've added electrolytes to it to help re-hydrate you," he is told - and he gulps it down, before heading off for qualifying.

The time he posts misses the cut and he does not make the race on Sunday. But, with his talent and determined attitude, it should not be long before the Irn Bru is replaced with a magnum of Champagne.