I just bought a Yakima Spare Time bike rack and the upper tube adaptor. I have a Specialized full suspension bike, when I install the top tube adaptor and place it on the bike mount it doesn't seem stable. I know I have on there correctly, but the tires spin and handle bars move. Should I be worried? Should I try to bungee the wheels so the handle bars stay secure? It just seems sketchy after using a roof mount on my patriot which didnt move an inch.