What discount do you get in the ACO shop Mark?? And are you limited to how much you can spend at a time, i.e. could one member buy 20 ACO t-shirts for the whole of their group??
As wishywashyman said above - 10%.
I'm not aware of any limit!
You also get all the tickets at "series B" prices - giving further saving - if you can buy for 6 people (the limit) then you save a fair bit!
The Programme is included (so there's another £5 saved) and the "entry list" in the race pack is HUGE! This is A4 in size and includes (from memory) a double page per team, with all the stats and info on the car and drivers. It is the sort of thing that is given to journo's (in fact - they do a version for journalists).
Membership also gives you the ability to order ACO stand tickets (but there is a limit of 2).
I think it is VERY worthwhile.
