I have a 8'x16' with a 6' ceiling. It is set up to haul 2 bikes with plenty of room for extra luggage. I don't like my bikes almost touching each other. If you want plenty of room where the bikes aren't almost touching, I'd look into the 7'x20' or 8'x20'.:kaz:
I was thinking of getting a v-nose which will give me a little extra. This way I could put one bike in the center and two a little further back on each side. The fourth bike could have the handle bars over the two outside bikes. Am I totally off, or is it doable? I know it would be tight, but I don't want them rubbing.... but then again, maybe when I got to where I'm going, I would open it up to find a few offspring V's.