First of all, YES, the tire water tanks do freeze. If someone tells you the tires do not freeze they are probably trying to sell you a tire water tank. Having said that, the tires do freeze less that a traditional concrete or plastic water tank. The rubber is about 6-8 inches thick and acts as an insulator. The tires also hold a large volume of water which takes longer to cool down and therefore is slower to form ice.
A few years ago, we put shade balls in the waterers to see if they would help with the water freezing. We ended up with mixed reviews. 
Pros:
  • They cut down on the surface area of the exposed water and served as protection from the wind
  • Help prevent freezing with temperatures getting down into the low 20s
  • They absorb sunlight and transfer that solar energy to small amounts of ice
Cons:
  • As the temperature drops below 20 degrees, the shade balls begin to get in the way when chopping the ice from the tire
  • The balls are not enough to thaw thicker ice
We developed a spring one summer that flows to one of the tire waterers. It is set up so that the water from the spring flows continually into the tire tank and then out the overflow at the top and back to the creek. The continual flow of this tire tank kept it from freezing completely. We did not have to remove ice from the tire waterer.  As you can see in the pictures the ice is of varying thicknesses and is still open where the inlet flow is disturbing the surface of the water and around the outlet pipe where water is moving. Although the opening is small, it is still enough that a cow can get a drink of water.​

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