A tracked work machine having an undercarriage assembly configured to drive the work machine over ground, the undercarriage assembly comprising: a drive wheel ; a front idler wheel rotatable on a front axle , the front idler wheel defining a front idler axis ; a rear idler wheel rotatable on a rear axle , the rear idler wheel defining a rear idler axis ; an endless track belt disposed about the drive and idler wheels; a plurality of supporting mid-rollers located between the front and rear idler wheels and configured to engage the endless track belt on a lower run thereof; a track roller frame pivotably mounted on the work machine with a main pivot defining a main pivot axis , the track roller frame comprising an elongate member with a front end and a rear end with the main pivot located between the front end and the rear end and the front idler wheel being connected near the front end of the track roller frame characterised by a major bogie connected to the track roller frame, the major bogie comprising a forward bogie arm and a trailing bogie arm and pivotably connected to the track roller frame at a major bogie pivot defining a major bogie pivot axis , wherein the rear idler wheel is connected to the trailing bogie arm, wherein the major bogie pivot is offset from the main pivot along the track roller frame such that the major bogie pivot is at a location between the main pivot and the rear end of the track roller frame; a minor bogie mounted on the forward bogie arm, the minor bogie being pivotably connected to the major bogie at a minor bogie pivot defining a minor bogie pivot axis , wherein a first of the plurality of mid-rollers is mounted on a front arm of the minor bogie and a second of the plurality of mid-rollers is mounted on a rear arm of the minor bogie; and a suspension cylinder connected between the rear end of the track roller frame and the trailing bogie arm of the major bogie. a drive wheel ; a front idler wheel rotatable on a front axle , the front idler wheel defining a front idler axis ; a rear idler wheel rotatable on a rear axle , the rear idler wheel defining a rear idler axis ; an endless track belt disposed about the drive and idler wheels; a plurality of supporting mid-rollers located between the front and rear idler wheels and configured to engage the endless track belt on a lower run thereof; a track roller frame pivotably mounted on the work machine with a main pivot defining a main pivot axis , the track roller frame comprising an elongate member with a front end and a rear end with the main pivot located between the front end and the rear end and the front idler wheel being connected near the front end of the track roller frame a major bogie connected to the track roller frame, the major bogie comprising a forward bogie arm and a trailing bogie arm and pivotably connected to the track roller frame at a major bogie pivot defining a major bogie pivot axis , wherein the rear idler wheel is connected to the trailing bogie arm, wherein the major bogie pivot is offset from the main pivot along the track roller frame such that the major bogie pivot is at a location between the main pivot and the rear end of the track roller frame; a minor bogie mounted on the forward bogie arm, the minor bogie being pivotably connected to the major bogie at a minor bogie pivot defining a minor bogie pivot axis , wherein a first of the plurality of mid-rollers is mounted on a front arm of the minor bogie and a second of the plurality of mid-rollers is mounted on a rear arm of the minor bogie; and a suspension cylinder connected between the rear end of the track roller frame and the trailing bogie arm of the major bogie. <EOS>