When to Get New Tires
If your tread depth is legally bald (1.6mm), they are no longer safe and must be replaced. All season tires should be at approximately 3mm depth, winter tires at 4mm. Consider what kind of surfaces you typically drive on when deciding to get new tires.
Most cuts and punctures can be repaired and will not require replacement, but if there are bubbles, blisters, bulges, large cuts or cracks you should have your tire professionally inspected. Damaged shoulders or sidewalls usually indicate the tire will need to be replaced.
Never use any tire that is more than ten years old, regardless of their condition. Do not use tires that have not been worn in six years, including unused never mounted tires that have been properly stored. Tires that have been in use for five years or more should be inspected regularly. Most vehicle manufacturers recommend replacement at six years.
Tires that have been driven on while flat or with extremely low inflation will suffer a weakened internal structure and become more susceptible to sudden failure. These tires should not be driven on and replaced as soon as possible. Even if they outwardly appear to be structurally sound, there will be internal damage.