It's impossible to group cars without knowing who will turn up and when. If I knew that all 30 cars would be here first thing, I would do a running order.
I will have to do it as I said earlier, people arrive, fill the form in and hand it back to me. I will number the forms as they are handed back, but will juggle people around that want to have their run earlier/later as necessary.
So, to re-iterate, upon arrival, please make your way to fill a form in as quickly as possible if you want an early run.
