Of course most of us would prefer to buy used tires for our cars since they are much cheaper than the new ones but before getting into it one should be aware of the tyre laws prevailing in your state and ensure that the old tires sold to you maintain the legal tread limit specified.
Tire law specifies the required legal tread limit for the tires; for example, in UK it is 1.6 mm across the center and ¾ of the width of the tire around the circumference of the tire. No bulges, cuts, crack or other signs of damage should be visible on the tires since they could affect the safety.
If you are plying your vehicle with tires that have past the legal tread limit you can be fined and penalty points too will be levied on your license in case the police stops you.
Part worn tires are those that have been previously used on another vehicle. They are sold at affordable prices and are almost 50% less than the new ones and depend greatly on the tread left on them. There are people who think that it is better to opt for used tires with a better tread than the tires that their vehicles are having at that time with a lesser tread.
Part worn tires are mostly important from Europe where some of the countries have a much higher legal tread limit than UK and other countries; these are mostly sold directly on online auction sites from the exporting country itself. But in this there is a bit of a disadvantage; you will have no idea about the history, condition or age of the tires and will be ignorant of internal defects existing if any and this could prove to be a safety hazard for you. Tires that have been involved in accidents could have structural damages that are not visible from the outside, so be ware while buying from here. It is always good to maintain your tires instead of replacing them with new or old tires.
Apart from changing your tires before they reach or pass the legal limit, it is essential to maintain them for longer life. Inspect them regularly and remove stones and other debris from the treads. When you notice uneven wear take them to a good garage for investigation and rectification of the cause.
Inflate your tires to the specifications spelt by the manufacturer for preserving tire life, safety and for good maintenance. Check your tire pressure at regular intervals, remember over inflation expands the tire reducing the amount of tread in contact with the surface of the road and further decreases the sidewall flexibility. Whereas under inflation increases the overall diameter of the tire and increases the flexion in the sidewall resulting in poor handling of the car. Both of them are not good for your tires and will compromise on the safety and longevity.
Finally, take advise from your garage and go for the tires recommended by them; they suggest a range of either old tires or new ones depending on your budget and your driving condition for a happy and safe driving!