You can transport 2 bikes in a 6x12, but it's a tight squeeze on the sides. We have a 7x14 and it's nice and roomy for 2 bikes, gear, and the scooter. Depending on tie down points, we could probably squeeze a third bike in there, but it would be staggered, which can make finding tie down points difficult. I have transported 4 comfortably in a 7x16.