I wouldn't mind having some of that slime in my rear tires (not sure of the brand name, but it's safe for the rims). Only issue with the added weight is what it would do to my yard. I don't mow my lawn with the tractor, but I do need to cross now and then hauling various items. In spring when it's damp, it causes depressions in the soil even with the wide 17.5" R4 tires. In a perfect world though, I'd love to fill the tires...but I'd be paranoid about using anything other than a slimy gel or something like that specifically made to not corode.