Bike Carrier Regulations - Western Australia
Each character (letters and numbers) of a number plate must be clearly visible when the vehicle is used on the road. If you attach a bike rack or mobility device rack to the rear of your vehicle and it or the load obstructs any character on the number plate from being read, you will need to purchase and affix an auxiliary plate.
Your auxiliary plate will display the same characters as the number plate issued for the vehicle.
Similarly, you should make sure that your lights are not obstructed which may require the purchase of portable rear lights.