In 2011I was riding on my Kawasaki Versys 650 and just remembered someone telling that Mondays are now full-day motorbike days, so I rode to the main entrance of Bira Circuit in Pattaya. Although in the week of Songkran (Thailand's biggest festival) the track was open, but I had to take the back entrance to get to the pitt. The back entrance is actually about 100 meter before the main-entrance although I do not believe there is any sign along the road. After passing the entrance (and ignoring the sleeping security guard) I did ride trough a tunnel under the track and riding after a small road I was suddenly in the pit. There were a few bikes on the track, mostly ridden by semi-professional Thais on their special racing bikes. There was one western guy riding his Kawasaki ER6N. For only 1.200 thb you can play here all day with your own bike. Of course you will need to be wearing a helmet and other protective cloths.
Bira circuit is not only a racing circuit for motorbikes and cars, but they also have a professional kart track. I will check that out next time. Bira racing circuit is located along route 36 about 12-km from Pattaya, actually it is at the very end of "Siam Country Club".