On entry, you nominated a time. mine was a complete guess of around, but not under 2:00.
Groups seemed to be based from this into 3 categories.
Slow, medium and fast.
Of course, even in each of those there will still be quite a difference.
No nominated time from me because I was a PI newb, just like a few others. But car specs, lap times at other circuits and driver experience should give a fair indicator. Anyway, basically I'm just trying to give some feedback. Having been involved in Nationals myself I know it's not easy.