A vehicle having a steerable suspended caster wheel, the vehicle comprising: a chassis ; a subframe independently suspended from the chassis to allow the subframe to move relative to the chassis as the vehicle travels over uneven terrain; a caster wheel assembly rotatably mounted to the subframe at a swivel joint having a steering axis (B), the caster wheel assembly comprising: a leg assembly ; and a caster wheel rotatably mounted to the leg assembly by an axle , the leg assembly and caster wheel being rotatable about the steering axis (B) through a range of swivel positions; a steering actuator connected to the caster wheel to selectively control the swivel position of the caster wheel ; and a steering mechanism connected to the steering actuator to control the steering actuator ; characterized by : a disengagement system which selectively enables the steering actuator to change the swivel position of the caster wheel in response to movement of the steering mechanism in a caster wheel steering mode and disables the steering actuator from changing the swivel position of the caster wheel in a non-caster wheel steering mode, the disengagement system comprising a variable length cylinder connected between the steering actuator and the caster wheel , the variable length cylinder being in a locked position in which the variable length cylinder is at a fixed length in the caster wheel steering mode, the variable length cylinder being in a float mode in which the length of the variable length cylinder varies in the non-caster wheel steering mode. a chassis ; a subframe independently suspended from the chassis to allow the subframe to move relative to the chassis as the vehicle travels over uneven terrain; a caster wheel assembly rotatably mounted to the subframe at a swivel joint having a steering axis (B), the caster wheel assembly comprising: a leg assembly ; and a caster wheel rotatably mounted to the leg assembly by an axle , the leg assembly and caster wheel being rotatable about the steering axis (B) through a range of swivel positions; a leg assembly ; and a caster wheel rotatably mounted to the leg assembly by an axle , the leg assembly and caster wheel being rotatable about the steering axis (B) through a range of swivel positions; a steering actuator connected to the caster wheel to selectively control the swivel position of the caster wheel ; and a steering mechanism connected to the steering actuator to control the steering actuator ; characterized by : a disengagement system which selectively enables the steering actuator to change the swivel position of the caster wheel in response to movement of the steering mechanism in a caster wheel steering mode and disables the steering actuator from changing the swivel position of the caster wheel in a non-caster wheel steering mode, the disengagement system comprising a variable length cylinder connected between the steering actuator and the caster wheel , the variable length cylinder being in a locked position in which the variable length cylinder is at a fixed length in the caster wheel steering mode, the variable length cylinder being in a float mode in which the length of the variable length cylinder varies in the non-caster wheel steering mode. <EOS>