Here is an any% guide for the Jason Jarrett route. Retire from any races not mentioned in this guide, unless you have a reason to do them.

National level: you need to win all races in this route to qualify for the next level, otherwise you need to do one or more additional races.

German(Opel): Hockenheim/Nurburgring/A1-Ring/Hockenheim British(Nissan): Silverstone/Oulton/Brands/Oulton/Silverstone North American(Lexus): Watkins Glen/Road America/Vancouver/Watkins Glen/Laguna Seca

International level: you can finish 2nd in one of the races in this level without having to do an additional race. Sugo is significantly harder than the rest for some reason, you may want to replace it by another Asia-Pacific race, such as Adelaide.

Pan-American(Lincoln): Laguna Seca/Watkins Glen/Vancouver/Brazilia European(Renault): Hockenheim/Dijon/Nurburgring/Silverstone/Brands Hatch Asia-Pacific(Ford): Bathurst, Sugo, Ti-Aida, Bathurst

World level: Ideally you can finish this level on 4 races, but this is depending on RNG. You can do it on 5 or 6 races if you want to take it safe. If you're on the 4 races route, you will likely need to wreck Justin Labonte in the blue BMW a few times, as he's your most dangerous opponent. You can use your saves if you need a safety net.

World(Renault): Vancouver/Silverstone/Watkins Glen/Hockenheim. If you need one or more additional races, you can do Buenos Aires and/or Monza.

Setup guide:

Lowest possible downforce. Maximum front brake bias. Longer gears. 1 to 3 clicks softer anti-roll. 1 to 3 clicks softer suspension.

You need to set-up your car at the beginning of each championship.