Which configuration has a minimum stability of 75%?

• A. On Rubber
• B. On Outriggers
• C. On Rail Clamps
• D. On Tracks

Answer: (A)

When thinking about stability, the key idea is how the crane’s base and ground support affect tipping risk. Being on rubber means the crane isn’t using outriggers or any stabilizing spreaders; it sits on tires, so the footprint is relatively small and ground conditions can shift more easily. That makes the setup less stable, so you restrict the lift to a lower fraction of the rated capacity. In many practice contexts, this configuration is assigned a minimum stability of 75%, meaning you should not plan lifts beyond 75% of the rated capacity for safe operation.

Configurations that use outriggers, tracks, or rail clamps spread the load over a larger, more secure base or mechanically anchor the crane, which greatly improves stability. Those setups typically have higher minimum stability values, allowing more of the rated capacity to be used safely.