Clever design: This Camco Curved Trailer Aid allows you to change a flat tire on a dual-axis trailer, without using a jack. You simply drive over it with the wheel next to the one that needs changing, then chock the yellow part in place with the black part, which has a rubber base pad for friction.It provides 6.5" of lift, so even if the target axle sags, you've still got plenty of clearance to get the wheel off. Runs $55.