Early bird catches the worm !
For most of my panning shots I use manual focus even with my fast lenses
I pre focus and lock in my exposure on the part of the frame I wish to get the shot then when the car comes round I track it and usually fire off a three round burst and if all goes well the middle shot should be the sweet one
If you can't make this one then the start of next season at Brands will be in March and Ros and I usually attend, haven't missed it for the last five years anyhow