/ plain water in tires. #31
When burying a propane tank ya gotta attach a magnesium or zinc anode to it to prevent it from rusting.
Steel hulled boats get anodes bolted to 'em to prevent rust.
Now I've never inspected a buried tank or the steel hull of a boat, so I'm spitballing here.
But what about attaching an anode to the lug bolts of the tractor tire? Skip the Beet juice or other expensive stuff and use plain water?
The main considerations with tire fluids appear to be in this order, based on the popularity of the various liquids used:
1. Freezing point
2. Corrosion potential
4. All other considerations (density per gallon, toxicity, flammability, hassle of handling, availability, etc.)
The main liquids used are plain water, calcium chloride dissolved in water, methanol/water (this includes windshield washer fluid as well as industrial methanol mixed with water), and beet juice. From what I have seen methanol/water is the most common overall, with calcium chloride in water being #2, plain water being #3, and beet juice being #4.
Freezing point is absolutely #1 in the list of concerns. The issue with running plain water in tractor tires is that it will freeze and ruin your tire if you live in an area that gets below freezing in the winter. This is the major reason why people put any liquid with a freezing point of well below 32 F inside of their tires. Plain water is absolutely used in areas that do not get below freezing as it is dirt cheap, safe, very minimally corrosive, and easy to deal with. Everything else is far more expensive than water and more of a hassle to deal with in some way, so people use them because they have to rather than because they want to, in nearly all cases. The other liquids used have freezing points typically in the -30 to -50 F ranges which is why people bother with them instead of plain water. Methanol/water in particular can have a very low freezing point, it is -40 F at a typical 50/50 mixture but in very cold areas it can be decreased to almost -190 F at an 88% volume/volume mix with water.
Corrosion is the #2 concern based on what fluids are being used today. The main liquid used in the past in tractor tires was the highly corrosive calcium chloride in water as it was the least expensive fluid with a freezing point below that of water. The reason calcium chloride is so corrosive is that a typical mixture has at least 1000 times as much dissolved electrolyte in it compared with typical unsoftened tap water (3 1/2-5 pounds per gallon vs. at most 0.0042 lb/gal [500 parts per million] and often much less than that) and these electrolytes plus oxygen cause rust. Tires filled with calcium chloride typically take a few decades to rust out rims, which is why calcium chloride went from being the liquid to fill tires with to being less commonly used today.
Cost is the #3 consideration as the most popular fluid by what I can tell is methanol and water, which costs roughly 85 cents/gallon at a typical 50/50 mixture. Water is less than a cent a gallon, calcium chloride and water is roughly 50 cents/gallon, beet juice is over $3/gallon.
Other considerations are as a whole below the first three. If simply adding the most weight per tire was paramount, then people would be using calcium chloride in water as it is the heaviest at up to a touch over 13 lb/gallon at the higher 5 lb/gal mix rate. Methanol/water would certainly not be used as it ranges from 7.5-8 lb/gal at a 50/50 mix, depending on temperature, which is lighter than water and whole lot lighter than beet juice (11 lb/gal) or calcium chloride in water. It would also not be used if toxicity and flammability were a concern as drinking two ounces of a 50/50 mix will kill most adults and it has a flash point of just above room temperature.
The reason sacrificial anodes aren't used in a tire with water is that the corrosive potential of plain water in a tire is very small. There are few electrolytes in the water, and remember the water stays in the tire, so once the tiny amount of dissolved salts have their redox reaction with the wheel rim, there are no more new unreacted salts to carry on further reactions. A big tire might have a few hundred gallons of water in it. This is completely different than a water heater, which in its typical 15 year lifespan may have a few hundred thousand gallons of water run through it, and thus needs its sacrificial anode to avoid rusting out the tank, or a boat that goes through a huge saltwater ocean (and saltwater has a lot more ions than tap water) and has anodes to avoid rusting out the hull.