Bike covers create a big problem for bike racks. Due to the huge amount of wind they capture when travelling at 100klm/h, (not to mention on-coming winds and trucks passing etc) the force applied to the bike rack is too great, and may cause damage to the centre tilt pole, and damage to the mount system. If you are determined to cover the bikes, wind MUST be able to pass through the cover. A solid canvas style non venting cover will void your warranty.