JD offers two different types of wheel weights to fit the 26x12x12 wheel setup on the X series. One is a 72 pound "starter weight" which is steel and the the other is a plastic covered 50 pound weight. The 72 pound is my recommendation as they are cast iron and very durable. They also have additional hardware such that one can mount either one or two additional weights to the 72 pound starter weight. With a 72 pound weight and a 50 pound weight and potentially liquid ballast in the rear tires one can add about 350 pounds of rear ballast, which is plenty for this sized machine. When I had my 595 with a 45 loader on it, the addition of even a 72 weight and rim guard in the rear tires really made a difference in stability with a heavy bucketload of mulch or rock.
Another option for improving traction/balance is to install suit case weights on the rear of the X485. This is what my dealer recommended and what I did when the front mounted JD 47 snow blower was installed on my X485. It made a tremendous difference. The suit case weights are a snap to put on and remove, and you can adjust the number of weights as you need. I also put rubber strap type tire chains on the rear wheels which worked quite well -- rubber straps instead of actual chains to prevent marking up the concrete and asphalt driveway.