Final answer:
The most common crossmember spread in a van semi-trailer's sub-frame is usually around 12 inches on center, which balances strength and weight efficiency. This can vary based on design, cargo, and regulations.
Step-by-step explanation:
The most common crossmember spread used in the sub-frame of a van semi-trailer is typically around 12 inches on center. This spacing can provide a good balance between the strength of the frame and the weight of the trailer, which is important for maintaining the structural integrity while being efficient for cargo transport. However, it can vary depending on the design requirements, the specific cargo being carried, and the regulations of the region in which the trailer operates. The crossmembers play a critical role by supporting the floor and load, and by contributing to the overall rigidity and durability of the trailer.