I agree that a national set of rules for VTA in Australia would be great, the track I run at is an ex Nitro track so it's quite large (had the Nats there last yr) so to run a 21.5 there would probably result in many of us falling asleep (but if a natural rule set was adopted and we followed suit I'd gladly change over), unlikely you'd ever have to let off the throttle. That said on 17.5 tyre wear is much more pronounced, a set of fronts will last you maybe 2-3 club days.