In Adelaide 4x is non existent apart from the Eagle Nationals. Started taking my hardtail to the 2 local bmx tracks last year and when i looked into it further discovered under uci rules that mtbs are full legal for cruiser class. Been doing lots of clubbies and trying to race as many of the state series rounds with the intention of racing state titles and possibly nationals start of next year in cruisers. Raced state series round at the beginning of the year on my Tazer dually (won't do it again, too slow haha) and raised a few eyebrows. Not many people are actually aware mtbs are legal for cruiser class but one look through the rule book clears that up. Best training for 4x, here in Adelaide all clubs train and race "every" week!!
Posted a helmetcam vid in the video section showing a clubbie final if you're interested