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, and the said wheel is adjustable. Also provided is a wheelchair, wherein a ground-engaging wheel on each side of the wheelchair is provided with a brake. Also provided is a wheelchair or other wheeled vehicle in which one or more ground-engaging wheels are provided with ratchet means. 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.
