I swear by these things, although I use a 3 inch piece of PVC. It seems to work well and I have never had any problem with it moving during transport. I personally think that it is a LOT more stable with the PVC in place, as the bike wont bounce, wobble, or lean when the vehicle hits a bump or takes a corner. I further believe that it puts less pressure on the tie downs due to the pressure on them remaining somewhat static (as compared to bouncing, etc). Between that and running carabiners on my tie downs (so the hooks cant come undone), I feel much more confident when traveling. Nothing like having a bike come off of the trailer once to make you extremely particular about how they are strapped down in the future. As a side note, I do believe that it helps the fork seals somehwat.