The internal rack width is 47' and 285mm x 4 = 45 inches. If 285 is the width of the tread pattern and the actual tire is wider than 285, then we'd imagine you should probably get the 6 foot rack. Even if they fit in the 4 foot rack, we think you should expect getting those tires to fit into that rack will be like trying to jam Shaquille O'Neal into a Smart Car. Thanks Chris.