The present invention provides a tag axle attachment for an off-road agricultural vehicle. The tag axle attachment allows agricultural vehicles to meet roadway weight restrictions imposed by the federal and state governments while also allowing the vehicle to perform optimally in the field. The tag axle is assembled such that it can be hydraulically lowered into a deployed position when the agricultural vehicle is on the roadway and hydraulically raised into a stowed position when the agricultural vehicle is in the field. The tag axle assembly is mounted to the chassis rails of an agricultural vehicle and positioned to fit between the chassis rails when stowed and minimizes the load per axle of the vehicle when deployed.