There are carriers that attach via straps I have never used one.
the beak style carriers id you carry more than one the bikes can rub on each other causing paint damage.
also the clamp on the top bar can cause paint damage if you are not careful.
Anyone hung one of these carriers off the back of a sedan? I'd like to mount one on the MG, and even if I did fit a towbar (my last MG had one), it wouldn't be strong enough to carry bikes.
I picked up one of these to use on my Diahatsu the other week. I see they are still on special at Anaconda Mile End or via www.anaconda.com online ordering. I still have to work out how to put a number plate on the back. The 2 bike is $52 or 3 bike $56. Perhaps ring before you go down or order online. PH 8152 0522. If you not an adventure club member you can sign up at the front counter to receive a card to get the discount.
Cell quite often have these for about $80. I use mine on a hatchback but it should work on a sedan. I use carabiners to attach the number plate to my bidon cages. They use faairly heavy duty straps to hold the cross bar onto the carrier so unlikely to crush carbon.
Sorry Simon should have been www.anaconda.com.au or directly to the bike racks
Look for Saris Bones 2 Bike Rack. I took my carbon bike to Melbourne, Canberra and back to Adelaide via the Hay plain on the back of my hatchback which cannot have a towbar. I protected the paint by placing a piece of cardboard (next I will try that headlight plastic you can buy in car shops) on top of the paint for the bottom legs. The other leg goes on the window. There are 6 support straps. I spent a long time looking at options and chose this one and so far happy to have done so. You can even open the hatch with the bike on it and the number plate is not obscured at all. I checked this plate issue by mounting the bike and showing it at my LBS and he insisted I do not need a plate.
You can use a thin piece of wetsuit material on the metal clips to stop any scratching or cut up a stubby holder.
The straps are quite long. You may be able to bring the straps to the inside back of the car and say use a child restrain harness point and attach there. I certainly wouldn't attach it to just glass at the top.
What kind of car is it?
Otherwise you may have to use some roof racks with bike mounts. Roof racks are $200 to $250 even without the bike mounting attachment.
We have one of those Anaconda racks with the straps and hooks and it works pretty well. We usually put a towel underneath the contact points to prevent the rack from rubbing on the boot of the car. It's not as solid as a towbar rack but it handles 3 mountain bikes pretty well. The only problem we had was with the brackets that you get with it not fitting the thick tubes of our bikes. We usually just set the bikes on the bars and use octopus straps to hold them down. I've been thinking about removing the brackets completely and wrapping the rack bars with foam rubber to protect the bikes. Perhaps with some thicker pieces to keep them separated.
You may also have issues with smaller adults bikes or kids bikes. The width between the bars isn't adjustable and my wife's mountain bike barely fits.