The only two "official" challenges are Team GTPlanet and the GTPlanet Race Series. The GTPlanet Race Series is a very complex challenge organized by Talentless, so check in with him if you're interested in competing. Team GTPlanet isn't necessarily a challenge on it's own, but it's a collection of the very best drivers from the site who will then go on to represent GTPlanet in challenges with other online forums. 
and if you really are interested in racing then go to the link below and have a try at the courses i posted and post your times , if your good you'll get on the leaderboard 
and it gives us a rough idea of how good you are 
have fun man and welcome to gt planet 
