<P> In some other vehicles, automatic locking hubs are used which, as the name implies, engage automatically when 4WD is desired . The main advantage is that the driver does not need to leave the vehicle to connect the wheels to the axle . The disadvantage with this system is that most designs require the vehicle to move some distance (usually a whole wheel turn, often going backwards) after engaging the hubs in order for the hubs to engage or disengage . This might not be possible if the vehicle gets completely stuck before the hubs have been engaged, meaning automatic hubs require more caution on the driver's part . </P> <P> Locking hub mechanisms also generally extend further beyond the wheel than most axles, and exposed hub locks can be broken or damaged by off - road conditions, rendering 4 × 4 useless and leaving the vehicle stranded . Also, in some axle designs (such as those used on older Land Rovers), the top swivel bearing can become starved for lubrication (which is normally supplied by oil slung up by the rotating axle), unless the hubs are locked every few hundred miles . Also, since locking hubs generally do not require a key to operate, they can be maliciously locked or unlocked by persons other than the vehicle owner . </P>

Why do you have to lock the hubs