Patent ID: 8020648

Claim:
An agricultural tractor comprising: a tractor frame arranged for attachment to an implement to be moved in a longitudinal working direction across the ground; a first pair of ground wheels mounted on the frame at positions spaced transversely of the frame on either side of a center line of the frame; a transverse beam mounted on the frame at a position spaced longitudinally from the first pair of ground wheels; a second pair of ground wheels mounted on the beam at respective ends thereof; the beam being mounted on the frame for pivotal movement about a substantially horizontal axis along the center line of the tractor; each of the second ground wheels being mounted on the beam by a respective castor assembly; each of the castor assemblies comprising: a transverse axle of the wheel, a pivot member having a vertical rod defining a vertical pivot axis mounted in a swivel support of the beam and a bottom transverse member connected to a bottom of the vertical pivot rod, a mounting link interconnecting the bottom transverse member and the axle such that the axle is located below the pivot member and, in respect of a forward direction of movement, in a plane radial to the vertical pivot axis and rearwardly of the vertical pivot axis, the mounting link including a torsion spring allowing spring suspension pivotal movement of the upper ends mounting link relative to the bottom transverse member about an axis parallel to the wheel axis.