what are calcium filled tires?
Here ya go.
(I did not author this, but rather borrowed it from another web site.)
There are two methods of obtaining sufficient rear wheel weight. The first is the time-honored tradition of filling the rear wheels with Calcium Chloride solution. This is a non-freezing liquid solution. By putting it inside your inner-tube, the weight is carried as low as possible which is good for the tractor, traction and safety. Unfortunately, once you fill the rear tires, you must watch carefully for leaks and attend to them immediately. I once spilled a small amount on the painted bumper of my truck when loading a leaking rear wheel. It was completely rusted in two-days. When this solution comes in direct contact with metal, a highly destructive process begins immediately and if left unattended, will destroy rims, hubs and whatever else it touches very quickly. Because of this and more serious safety concerns, filling and caring for your wheels is a job for your tire store unless you have a backhoe or very large loader (on a separate tractor). Lifting a filled wheel into your pickup bed is an operation that when done without equipment is reminiscent of building the pyramids. The only safe way to deal with a tire that is filled is to leave it on the tractor and have your tire company bring their rig out. They will drain it, remove and fix the tire, and refill it. Surprisingly it costs only a little extra to have them come out and it could save you some real headaches. If you have ever seen a large filled tire fall over, it will make the above believable to you.
The second way to get necessary weight on the rear wheels is through the use of cast-iron wheel weights. These come in two styles, one piece and multi-piece. A one piece wheel weight is simply a large round piece of cast iron that will bolt to the rim. On some machines you can add more than one to each side to gain even more weight. The real disadvantage of one-piece wheel weights is that they are heavy and unwieldy and thus difficult to mount and unmount. To overcome this problem, manufacturers cast wheel weights in many smaller sections or wedges that when installed would all add up to even more weight than a one-piece weight but individually were not as heavy. Generally it is easier to find one-piece that will fit your rims since they don't necessarily have to have been made specifically for your tractor to fit. With multi-piece weights, you are best off locating original equipment weights.