<font color="blue">It is a better alternative than foam (in most cases) because it has more give and I believe it is cheaper. </font>
Although I don't have foam in my rear tires, I am really a fan of foam, so I don't think that liquid is a better alternative to foam fill except that like you said it is going to be cheaper.
Foam actually offers more weight, since the tire is totally filled, as compared to 75% filled for liquid. It also takes away any worry about punctures and how to deal with them once you have that HEAVY liquid filled tire on your tractor. And there are no sloshing issues, not that sloshing in much of a concern anyway.
Foam is also forever...no taking it back out after you put it in... /forums/images/graemlins/shocked.gif That COULD be a negative...
Foam would have cost me 4 or 5 times as much as do-it-myself filling with WW fluid (granted RimGuard would be better) did, so liquid in the rears was the way I went.
But for the smaller front tires, it is hard to beat foam fill. It is not crazy expensive, since it is priced by the pound and the small tires are, well, small. But more importantly for me, the small fronts puncture A LOT easier than the rears, at least in my experience.
I have also noticed that my form filled fronts (BX and
B2910 ) still have some flex to them.
For me, the best approach was foam in the fronts and WW fluid in the rears...I did not have a source for rimguard, and did not want calcium because of the possible corrosion issues.
By the way, it would have cost me about $112 per tire to have the BX rear tires foam filled. I elected to use WW fluid for cost reasons. Now I wonder if I should have foam filled them. I like foam that much...STill, since it only cost about $40 or so for the WW fluid, I guess I do know the answer...WW fluid sure is cost effective...