Originally Posted by
jadocs
FYSA:
If you are going to use it for 3 or more bikes, you are better off getting the double rack then add up to two singles. According to 1UP it is sturdier than getting a single and adding up to three more singles.
For 4 bikes... yes, you need to start with a double (they are pretty clear about only using two add-ons). But for three you use a single as the base.
If you only transport one bike a lot of the time, a single has an advantage over a double as it folds up completely out of the way on most cars. No need to move it to get in and out of the rear of your car. This was the main selling point for me for buying the 1UP at all.
YMMV