if you decide to use something, an 10-12 inch piece of 4 inch pvc works great. That said, I rarely use mine anymore. Without starting multiple debates over everyone else's beliefs, issues, etc...., it seemed that my front bearings would need replacing more often (2 to 3 times per year). My theory is that if the bike has a fork brace, all energy from the movement of the trailer will be absorbed through the weakest link (bearings). At least without using the brace, the bike can actually move a litte using the suspesion. I did, however, invest in some tie downs that loop over the bars and connect to a carabiner. this allows me to keep the bikes from coming undone during transport. fwiw.