At regional level racing, you can race on whatever you want really. This is a really great way to be able to get into the sport, try it out and see if you like it befire comitting your whole life to it. Mountain bikes, adventure bikes, cyclo cross bikes are all permitted. You may even want to ride a road bike but you dont see this very often as you do need some grip on the track and are chunkier tyres are helpful. Riders generally opting for tyres up to 33mm for maximum grip. If yyou are riding a mountin bike then this will vary.