I'm in auto recycling and a constant prob. is the yard cars that the parts pullers run around in always have flats. "No flat" type of aerosal sealents dont help, often the holes are pretty big.I can have the tires filled with poly foam but that costs $ 150.00 per tire. Anyone have any ideas I could try? Top speeds are about 25 mph and they run on hard packed dirt. I've googled extensively and no luck. Let's say a max.cost of $50.00 per tire to solve this prob. Any ideas ?