I'm looking for some advice on the pros and cons of switching to flat free front caster wheels on my 7-year-old Gizmow 61" ZTR, which I use for both lawns and rough work. The mower has been remarkably resistant to my abuse, it does a nice job mulching grass, and it is very stable when mowing slopes. I do have fairly frequent flats on the front casters when I do really rough work, such as mowing the briars and small saplings on the back side of my dam every year or two. I have been thinking about replacing the front caster wheels with flat-free tires such as Marathon 13x5.0-6, which are filled with solid polyurethane. The owner's manual specifically advises against foam filled tires, which it says may cause failures to the hydro drive system. I assume it is referring primarily to the rear wheels, and I don't think that voiding the warranty is a big deal on this old machine. Any opinions on the tradeoffs in replacing the wheels?