cos i didnt think i'd be able to get them up on the roof. we got a thule... it's great cos with the ones where they hang down i always had to take my front wheel off cos it was too low to the ground.

This one locks onto your tow-ball so you can lock your bike to the rack - which we've done.

Thule EuroWay 945/947
http://www.thule.com.au/products.php (click on towbar mounted)

You can get them for either 2 or 3 bikes, and they fold away as well.