A properly set up crane should have what feature regarding its tires?

A properly set up crane requires that its tires be off the supporting surface, as this is essential for ensuring stability and safety during operation. When the tires are off the ground, it indicates that the crane is likely properly positioned, on outriggers or pads, which helps distribute the weight of the crane and its load more evenly. This setup minimizes the risk of tipping or instability, allowing for a safer work environment.

Ensuring that the crane is on a firm and stable ground without reliance on tires for support is crucial in preventing accidents or equipment failure. It reinforces the proper functioning of the crane's hydraulic system and ensures that the center of gravity remains low, further enhancing safety.

In contrast, other options suggest either partial support by tires, which could lead to instability, or complete submersion, which could cause improper handling of the crane and potential hazards. Understanding these principles is vital for safe crane operation and compliance with safety regulations.