Quantum 6000z

I need new tires and want to know the size I should purchase for my power chair. Are foam-filled as comfortable as tube tires?

When I measure from ground to the top of my current tires, they measure a little over 13". Is proper replacement 14"x3.0x8? Are the brands similar in quality and durability, or is there a brand that lasts much longer? When tires are delivered, is the air pressure of air filled tires mentioned. Is it different for heavy people vs. light-weight people? I weigh 260 lbs.

Are the front and rear tires solid? What determines the time for replacement? Are bearing replacements required with new tires? How do I distinguish worn bearings? Thanks! Shab