I won't be there either!
Huw try this:
To adjust the slipper, remove the body and
insert a 2mm (or 5/64”) hex wrench through the center of the top deck (or through the bottom slot in the chassis).
Then, grab both of the rear wheels and rotate forwards to tighten and backwards to loosen. As you spin the wheels,
you’ll feel the motor click every ¼ of a wheel revolution. At the track, tighten or loosen the nut in 2 click increments until
you hear only a faint slipping sound for 1-2 feet on takeoffs.
Shamelessly stolen from the manual at:
http://www.teamassociated.com/pdf/ca...-preflight.pdf