An excavator's lift chart indicates a rated capacity of 5,000 kg at a 4-metre load radius when working over the side. The same chart shows a 7,000 kg capacity at a 4-metre load radius when working over the idler (front). Why is there a difference in capacity?

Question: An excavator's lift chart indicates a rated capacity of 5,000 kg at a 4-metre load radius when working over the side. The same chart shows a 7,000 kg capacity at a 4-metre load radius when working over the idler (front). Why is there a difference in capacity?

Answer options: ✅ The tracks provide greater stability when the load is positioned directly over the main frame's longest dimension.

• Working over the side requires less hydraulic effort, therefore increasing capacity.
• The counterweight is less effective when the load is positioned over the side.
• Modern excavators are designed to always have higher capacity over the idler for specific tasks.

Correct answer: The tracks provide greater stability when the load is positioned directly over the main frame's longest dimension.

Explanation: Working over the idler (front) or drive sprocket (rear) of the excavator, aligns the load with the longest dimension of the track frame, providing a wider and more stable base for lifting. When working over the side, the base of stability is narrower, thus reducing the lifting capacity.