Something to remember about chicken tractors is they are open on the bottom. If you set your wheels high enough to make the tractor easy to move, you will create a gap underneath that makes it easier for predators to get into the tractor. I set mine low to minimize the gap. I didn't have them at the front edge, though, the wheels were a few inches back from the front edge. That, combined with the tractor being low on the wheels, meant that I could lift the back end only just barely in order to clear the ground. I used lawnmower wheels, which do not pivot. My yard was also mostly clumps of crabgrass, so it was extremely lumpy. Moving that tractor was a pain in my butt.
On top of that, predation and rats were a problem. Sine the tractor has no floor, a predator can just get its little hands under the edge and pull out the chickens. I lost a ton of chickens my first year. I kept getting more chicks to try again. I still get anxious those first few days of transitioning chicks outside. I ended up putting a floor on the tractor, which takes away all the advantages of a tractor, and makes it hell to keep clean.
I am so much happier with a free standing, fixed coop. It is a fortress that is easy to clean. The girls go out during the day and are safe and secure at night. Good luck!
