If motocross racing has become a sport that you're interested in learning more about, there are a lot of avenues to pursue. You can learn about the different types of motocross bikes, such as the Jetmoto line, or you can find out about the riding greats such as Jeremy McGrath.
A Google search will return several million results on the search term "motocross". You can narrow it down to printed information such as books and magazines to begin your learning expedition with. There are a number of good biographies about the stars of the sport and a number of good magazines are found both online and off.
Speaking of online, you will find the Internet is the crown jewel for information about this sport. There are websites devoted to every racer and bike found in this sport. For example, Raceway ATV has a huge amount of information on their site that will help you get informed about riding styles, safety gear, choosing the best bike and helmet for your riding style and so much more.
Another fantastic way to learn about motocross is to find a track near you and go watch the motocross riders. If you see a rider and bike you like, make a note of the brand and after the race, ask the rider about their bike and gear, most riders will be glad to talk about the gear they use. Make a special note of the amount of safety gear the riders wear, they literally are protected from head to toe.
There is a lot of good information to learn about the exciting sport of motocross, best of luck to you in pursuit of your new interest!
