No, you can't. A bike rack is designed to keep the bikes upright. If you tilt a bike rack with bikes, the bikes will fall off. But if you want to tilt a bike rack without any bikes on it, you can use the following steps. First, remove all the bolts from the bike rack. Then, tilt it at a 45-degree angle. Last but not least, put in all bolts and tighten them up.