Formula 1 Car Racing comprises the fastest open single seater cars with the most experienced drivers. Formula 2 and Formula 3 were the equivalent of a B and C class below Formula 1. My boss was a Formula 2 racing driver in the 1970s but that grade does not exist today. Formula 3 is still in existence.
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It's called Formula One because it's to top formula in a category for a specific type of racing.
There was a Formula Two (F2) series, but it was replaced by Formula 3000 in 1985, which, in turn was replaced by GP2 last year.Several European countries have a domestic Formula Three (F3) series' and there is a European Formula Three championship