bka, I don't know the answer to your question but I suppose we will find out. We looked at a few cargo trailers (I think a featherlite, wells cargo, and some other) and they either had full length piano hinges or several hinges (more than 2) for the ramp doors. I don't know that we looked at any meant for hauling cars....more along the lines of snowmobiles or motorcycles.
Our door may be a little bit stronger than your average. We built everything strong. That being said, it would be easy enough to drop 2 hinges and go with 3 or even 2 but I am inclined to stick with the five right now.
