Abstract: Apparatus which permits one individual to mount and dismount large, off-highway tires onto and off of their respective rims. The present invention is particularly designed to facilitate the mounting of such tires in a more safe, efficient, and far less laborious manner than heretofore possible. This is accomplished by the provision of apparatus which exerts great pressure on the sidewall of the tire being mounted so as to uniformly depress same to enable easy insertion of the lock ring about the tire rim. A preferred embodiment includes a pair of hydraulically operated jacks for exerting the pressure, and a rigid bar linkage interconnecting the moveable pistons of the jacks with the rigid rim structure to provide relative movement between the tire and the rim. The rigid bar linkages preferably includes means which allow the apparatus to be adapted to a plurality of differently sized tires and rims.