In reply to Richard Wheeldon:
Best invention ever. A minute to fit, 10 seconds to remove, and about a minute to put the bike on. Fits on my estate car with a glass roof and on my wife's BMW Z4 - fork on the roof, rear wheel on the boot.
You need to tie one crank to a chain stay so that the crank doesn't turn and let a pedal touch the roof (I use a short length of old inner tube for the purpose). Fits pretty much any car that does not have a canvas or a ridged roof. Stable at speeds faster than the law allows.
I have a cable lock for it - a padlock at one end goes on the QR that holds the fork. The other end of the cable has a plate that you shut behind the car door.
I have a shed full of old roof racks and bike racks that cost far more than the Seasucker. It also travels, so on hols I can ride out to meet the family somewhere and get a lift back. For a while I had a padded bike bag that would fold up. That got folded, put in the hire car boot, luggage on top and the bike went on the roof on the Seasucker.