A roller assembly for applying force to the ground is disclosed. The assembly includes a body adapted to be mounted to a vehicle for moving the assembly, and supports including a first support member supporting a plurality of rollers for applying force to the ground, and a respective piston connected to each roller, the rollers connected via a respective pressure chamber to the corresponding first support member to resist movement of the pistons towards the first support member. The first support member pivotably connected to the body via a first axis such that pivoting movement of the first support member about the first axis as a result of a first torque about an axis has a component about an axis transverse to the direction of travel such that engagement of the rollers with the ground causes a second torque on the first support member opposing the first torque.