I had the same issue. Have the 1.25" factory receiver on my big horn. Lost the bikes twice due to violent bouncing. Had the receiver removed, and re-enforced with more steel welded on it, and it still failed due to bouncing. Finally had a bolt on curt 2" receiver mounted on the front of our RAM and no more issues ever. The bikes dont seem to have any affect on cooling that I have noticed. Found out that all bike racks, in the fine print somewhere void their warranties if you attach to the back of an RV due to bouncing issues.