The most common subcategory is the 250cc production bike class, in which "race-replica" motorcycles that superficially resembled the Grand Prix machines but have engines capable of meeting legal and reliability requirements for street use, have their road equipment ripped off and are raced.
Because each bike offers virtually identical performance, and they are relatively cheap to buy and race, it is a popular introductory racing category, particularly in Australia.
wikipedia.org dumped 2003-03-17 with terodump