It's no problem taking the road bike onto the track. Just swap out the coolant, and you can take it in the N or I class. The N class, you really have to be numb to wreck, because you're on a slow pace, following an established line. The I class is a bit sketchier, because any idiot can claim to be I, but there are fast people in there too. Ride to your abilities, and you don't need a bike collection to have a fast and aggressive day out on the track.