The wear and tear in tires comes from 3 main things.
1. Use. The constant flexing as the tire rotates (and twists) slowly weakens the belts in the sidewall.
2. UV. The UV from the sun breaks down the rubber and causes the erosion in the sidewall.
3. The air. Each tire has chemicals that are part of the "formula" these chemicals dissolve over time with exposure to the outside environment. This is the most common cause of "dry rot"
the tire warehouses are climate controlled and uv stable. The tires could sit there for years and not erode or dry rot. The real wear and tear on a steer tire is the twisting motion. The twisting is an even bigger issue with our long wheelbase trucks. This obviously doesn't start until the tire is mounted and driven.
Properly stored the UV and the evaporation process don't start until the tire is mounted.
Tire companies produce tires in batches. You might not find a "fresher" tire until they run a new batch of that particular model/size. The manufacture date is important to keep track of, but the in service date is the one most fleets base their maintenance off of.
I'm not telling you when to replace your steers, but just laying out the information that was given to me when I worked for the fleets. (20 years ago )
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