Consider changing your tires if:

1. Flat Tire: If driving feels abnormally bumpy, or a tire is flat.
2. Temperature: If the weather is consistently below 7°C (45°F) or above 32°C (90°F).
3. Tread Wear: If your tread depth has worn down to 1.6mm (2/32 inch) or less.
4. Tire Age: Even if your tires have sufficient tread depth, consider replacing them if they are over 6 years old, regardless of wear.
5. Visible Damage: Inspect your tires for cuts, bulges, or other signs of damage.

To proceed to the car preparation stage, ensure that you have checked all the necessary tools to change a tire. You may choose to also select any optional tools that may help you in this procedure.