Howdy!
Methanol and water is what my dealer uses in all their fluid filled tires. Been using it for several years now with zero complaints.
As an aside, I got to play with this stuff the past weekend. In some way, I was mowing and must have gotten a hidden limb sutck between the mower and inside rear wheel. It sheared the valve stem off at the base, and I ended up in a pool of mud with 3 wheel drive as the now deflated rear tire stood stationary around the rear wheel. With a heavey mower on the back, it took about 20 minutes to limp to level ground.
Upon dropping the mower, I drove home to get a jack and my 3/4in socket set. Jacked up the rear axle and then remove the wheel. It was still about 1/4 full, and man was that a bear to wrestly up a 7% grade to the truck. Not to mention getting it up into the back of my F350. Wheh! Tire dealer put a new valve in it, and aired it back up. Bolted it back on to find that one of the wheel bolts was cross-threaded from the factory and stripped on the way out. Grand... Anyway, need to get that fixed and get the tire filled back up next week or so.
My point? Dunno. Just was slightly related and I've got a new-found respect for the weight of even our smaller, fluid-filled tires. Calcium would have been even worse...
Later,
Jay