MikeF, I had some neighbors tell me that calcium chloride was illegal to use in tires now, but I've never checked to see whether that is a fact or not, or if so, if it's a regional or state law. It's heavier than water and anti-freeze, also highly corrosive and must be used in a tire with a tube. Being in Texas where I don't have much really cold weather, and am highly unlikely to be using my tractor if the temperature is below freezing anyway, I put 2 gallons of anti-freeze in each rear tire, then filled them to the 75% level with water. I just used the standard old ethlene glycol anti-freeze, but will not do so again in the future since there are non-toxic anti-freezes available now. And I did mine myself, but I have my own homemade equipment for doing it. If you've never done it, or seen it done, you may be better off letting the dealer do it. But if you want to do it yourself, I think most farm supply stores have the adapters for that purpose.
Bird