Self-propelled vehicles that include swiveling caster wheels and independent drive wheels are disclosed. The self-propelled vehicles are selectively steered in a caster wheel steering mode or a drive wheel steering mode. The vehicle includes a differential system that may include a differential valve that allows hydraulic fluid to be transferred between the left and right drive systems. The differential system may be operable during the caster wheel steering mode such as when the vehicle is driven for transport between sites.
