Bulk
From Wiki
Bulk space is a unit of measurement to show the amount of free space available in a vehicle or lockup space in town or camp lockup buildings.
All weapons, ammo and resources (food, water, fuel or other commodities) have a certain bulk applied to the space they take up. While tires that are installed on your vehicle takes up none of the available space IN the vehicle, if you carry tires in your cargo space, they will take up a certain amount of bulk space.
Armor does NOT take up available space inside the car but each vehicle is 'allowed' a certain amount of armor "bulk space" depending on the chassis. It is this outer bulk space that your armor load-out will fill.
