EVER pushed a shopping trolley around with one bung wheel that constantly sends the trolley into orbit? It’s the result of castor, or the relationship between the top and bottom mounting points of a front wheel. In a live-axle 4x4 it’s the difference between the top and bottom kingpin bearings; on independent suspension it’s the upper and lower ball joints. When the suspension is lifted as little as 50mm, it can throw that angle right out of whack, causing twitchy steering, tracking, and all sorts of dangerous issues. Aftermarket control arms, castor plates, drop arms and offset bushes are all bolt-on ways of getting it back into spec.