Great question — answering as the UphillTech team:
Max load is how much mass you can load the tires with. I.e. the mass of the rider plus mass of the bike plus the mass of any accessories. The load is approximately split equally between the two wheels so your total load mass would be 140kg (~308lbs). Quality tires would usually give you a max and min inflation pressure. You can probably take the 280kpa as a maximum value.
Full answer by Argenti Apparatus: https://bicycles.stackexchange.com/a/72806 (CC BY-SA 4.0).
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