In a unibody structure, what component acts as support along with the pillars?

In a unibody structure, the roof provides significant structural support in conjunction with the pillars. A unibody construction integrates the body and chassis into a single entity, which enhances stability and strength. The roof helps maintain the integrity of the vehicle's structure, contributing to its rigidity and safety during impact. Specifically, it assists in distributing loads and stresses across the entire frame, which is vital for maintaining the vehicle's shape and performance.

The other components, while important to the overall structure, do not play the same role in supporting the vehicle alongside the pillars. The chassis is typically a separate entity in non-unibody designs, the floor pan provides a base for the vehicle but is not primarily a support component like the roof and pillars, and the firewall serves as a barrier between the engine compartment and the cabin but does not function as a structural support element in the same way the roof does.