USED TYRES DISADVANTAGE ! The major problem of a tire that is old but otherwise has good tread and doesn’t appear to have defects is that things such as oxygen, ozone, water and UV light attack the tire and weaken the cords in the body. This may cause a tyre to fail when it is inflated. Something like a large truck tire exploding when you where inflating it and you were next to or over it could very well kill you. If you are driving and it fails the range of problems will range from the annoyance of having to change it to losing control of the vehicle. At the other extreme I’ve used very old and marginal tires on my land plow. It plowed a half acre once a year and the worse that was going to happen was that I would have to drag it out the field on a flat.