What is the difference between independent and dependent requirements?

Imagine a scenario where a production technician wants to produce 10 bicycles. He requires two tires to produce one bicycle. In this scenario, the forecast or independent requirement, assuming a pure make-to-stock strategy, is 10 bicycles while the dependent requirements is 20 tires. Basically, a dependent requirement is based on the demand for another item while an independent requirement is not based on the demand for another item.