Kimi Raikkonen may have opened a few eyes with his first test performance at the wheel of one of NASCAR's Truck Series contenders, but his former F1 rivals are still struggling to understand why the Finn has deviated from his recently-found rally career.

The 2007 world champion was immediately quick on his first outing in the #18 Kyle Busch Motorsports Toyota Tundra, raising suggestions that he could now make his NASCAR debut earlier than originally planned. According to the Toronto Sun, Raikkonen was matching times with NASCAR superstar Busch on the second day of testing at Darlington Speedway in South Carolina, prompting Joe Gibbs Racing boss JD Gibbs to muse that Raikkonen could be rushed into Sprint Cup action this season. Previously, the Finn's schedule would have seen him contest a handful of Truck Series races before moving up to the second-tier Nationwide Series.

"I think it's great having him come in the sport and kind of looking at it and feeling it out," Gibbs said, "Kyle is the right program to do it with. It's a good fit - and we can always help Kyle out with some cars down the future."

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While Jarno Trulli has shown interest in an American career post-F1, and Lewis Hamilton is due to swap seats with NASCAR legend Tony Stewart later this year, some of Raikkonen's former rivals continue to scratch their heads over the move, which they feel detracts from the gradual inroads he has been making in the World Rally Championship.

"I don't understand," Toro Rosso's Sebastien Buemi told Finland's Turun Sanomat, "I thought Kimi was focused on rally and then it's a completely different story. Did he change his mind? I guess the most important thing for Kimi is for him to enjoy whatever he is doing - and he will definitely learn to drive in NASCAR faster than in rallying."

While Nico Rosberg admits that '100 per cent for sure I will not do it myself because I know I wouldn't enjoy it at all', he admitted that, if Raikkonen was content, he would wish him all the best.