The supply of tires increases.

The demand for tires remains constant.

The equilibrium price of tires falls.

The demand for cars increases. This is because tires and cars are complementary goods.

Supply and demand are normally considered to be independent of each other. In other words, a change in supply will not affect demand.

There are cases where the assumed independence of supply and demand may not be justified. Suppose, for example, that suppliers of microchips believe that the Federal Government will increase tariffs on the chips. As a result, they begin to increase production. If demand is unchanged, the market price will fall. But what if consumers also expect higher tariffs and begin to buy more before prices go up. In this case both the supply and demand curves shift to the right. Prices will rise or fall depending on which shifts the most.