Some characteristics of an automotive tire are its Size, Material, Internal Construction (bias ply, steel belted for example), tread design, cost, expected life and weight. a) Which factors are important in deciding whether or not to buy a new tire for your car

Money available to the buyer is most important factor which needs to be considered. Also the quality of the old tires is considered before making a decision to replace tires. The life of tire is dependent on the running of the car plus the quality of the roads.  

Explanation:

The tire are replaced once they are damaged. The damage can be through accident, roughness of roads, extra mileage and other similar factors. Once the tire is damaged it is better to replace it by the new one as this can be harmful for the commuters to travel in a car whose tires are damaged. There can be puncture or even tire burst situation which could be a threat to life.