There are a few reasons you need crashbars, protecting the bulbuous and expensive plastic is one, protecting the rad is another. Here is a couple of pics. Left side rad, where you can see there is a simple holder the the male end of the rad attachment slides into. On the reverse side, you can see a plastic piece that bolts the rad and to the support. On a simple tip over, this is designed to absorb a certain amount of impact, and then break, which protects the rad from absorbing the forces but also means that you rad will now be hanging from the hoses. Not an earth shattering problem, zip ties are an easy solution, but for a long tour, I would make sure that I had crash bars, zip ties, or a spare plastic support.