i came across this while surfing about, is this bloke nuts or what??? one way of doing it i supose http://www.alcester-racing-sevens.com/trackday_wheel_bar.htm

i saw 3 "7's" travel to spa like that to do a track day, slicks on the roof rack...

It looks like a pig roasting spit

I have many friends in the Westfield Club who have a similar device, but horizontally mounting them rather than vertically.

Like that one.

on the way back from snetterton I once spotted a caterham with the spare wheel in the passenger seat...

Ned.

Bet that does wonders for the Seven's Aerodynamics down the motorway.!!

The concept and design are the IP of AR7E and Toby Robbins Engineering.
Does that mean you're not allowed to build your own. It's a rack FFS