A wheelchair comprising: three or more ground-engaging wheels and a user seat, the user seat forming a structural member or monocoque on which the ground-engaging wheels are supported wherein at least one of the wheels is connected to the seat by a support member, the length of the support member being adjustable during use.Also provided is a wheelchair or other wheeled vehicle, wherein at least one ground-engaging wheel is connected to a pivotable hub, the pivotable hub being attached to the body of the vehicle by a fixed pivot member and a laterally-adjustable pivot member, the position of the laterally-adjustable pivot member being adjustable to cause the hub to pivot and thereby adjust the camber of the said wheel.Also provided is a wheelchair, wherein a ground-engaging wheel on each side of the wheelchair is provided with a brake, each brake being connected to corresponding brake actuation means mounted on or near the users seat and arranged such that the user may operate a brake actuation means to retard the corresponding wheel independently of the other wheel.Also provided is a wheelchair or other wheeled vehicle in which one or more ground-engaging wheels are provided with ratchet means, the ratchet means being operable to allow rotation of the wheel in a forward direction and to prevent rotation of the wheel in a reverse direction.A coupling arrangement for releasably joining two structural members is also provided.Also provided is a wheelchair including a rear castor with a detent mechanism to bias the castor into a configuration in which it is parallel with the front wheels.
