How long can tires be stored?

depends on what there on, i have seen fifteen year old riding mowers with original tires. my tire guy says they are trying to pass a law that won't allow them to sell a new tire that's been on the shelf for over six years, rule of thumb is a tire that's driven on should be replaced after 5 years reguardless of its tread or miliage, something about the oils in the rubber break down and they lose flexibility, and begin to dry rot, i check mine with every oil change looking for weather cracks or bubbles, that is when you know it's time for new ones

Most manufacturers have a five year limit on warranties, so I would say five years is a pretty good rule of thumb