Outrigger
Hydraulic extending legs deployed from a mobile crane’s chassis to widen its base, transferring lifted load to the ground through pads and preventing tipping.
Outriggers are hydraulic legs that extend outward and downward from the chassis of a mobile crane before lifting. They have two jobs: widen the crane's effective base of support (so the load can swing further out without tipping the crane) and transfer the load directly to the ground through outrigger pads, taking weight off the tyres and suspension.
A typical mobile crane has four outriggers — one at each corner of the chassis — though some heavy crawler-mounted machines and large all-terrains add a fifth or sixth for extra stability. Each outrigger has independent hydraulic extension and lift; the operator can deploy them to different extension levels depending on site constraints (sometimes called "asymmetric outrigger setup," which derates the load chart).
Outrigger pads spread the point load from each leg over a larger ground-bearing area. On hard, well-prepared ground, the steel outrigger float may be enough; on softer ground, timber cribbing or steel mats are placed under the pads to spread the load further. Calculating ground-bearing pressure under the outriggers is a critical part of lift planning — exceeding the ground's bearing capacity is a common cause of crane tipping accidents.
Modern mobile cranes monitor outrigger extension and pressure electronically and feed the data into the load-moment indicator (LMI), which derates the load chart in real time based on actual setup. Buyers should confirm the LMI is functional and that all outrigger sensors and cylinders are sound, as repairs are expensive.