Portable tire changer system for a kart tire mounted on a metal wheel rim comprising an annular external channel that is formed by an external side wall and an inner side wall, which have respectively an external annular edge and an inner annular edge capable to engage airtightly respective beads (201, 202) of a tire, and forms an external cavity and an internal cavity separated by a central disc for fixing to a kart wheel hub, said system comprising a portable tire changer apparatus that includes: - a supporting base; - supporting means fixed to said supporting base, rotatable about an rotation axis and comprising a supporting plate, which has a respective upper face provided with a respective layer of non-metallic material, in particular plastic or rubber, and arranged for supporting said wheel rim on the inner annular edge thereof, and connecting means projecting from said supporting plate along said rotation axis and configured to be inserted into said internal cavity of said wheel rim so as to engage centring and fixing holes (110, 111) of said central disc in a mounting configuration of said wheel rim on said portable tire changer apparatus; said portable tire changer system being characterized in that it further comprises a covering element, in particular made of plastic, and a working lever, said covering element being configured to engage and cover at least said external annular edge of said wheel rim so as to prevent said working lever used for removing a tire from said wheel rim during a dismounting procedure to contact directly said external annular edge, and in that said portable tire changer apparatus comprises: - driving means fixed to said supporting base and arranged to rotate said supporting means about said rotation axis; and - mounting means comprising an arm, movable and having a first end fixed to said supporting base and a second end movable, and an introducer element fixed to said second end, made of non-metallic material, in particular plastic, and configured to abut said external annular edge of said wheel rim in a mounting procedure in order to allow inserting and mounting a tire on said wheel rim by rotating said supporting means. - a supporting base; - supporting means fixed to said supporting base, rotatable about an rotation axis and comprising a supporting plate, which has a respective upper face provided with a respective layer of non-metallic material, in particular plastic or rubber, and arranged for supporting said wheel rim on the inner annular edge thereof, and connecting means projecting from said supporting plate along said rotation axis and configured to be inserted into said internal cavity of said wheel rim so as to engage centring and fixing holes (110, 111) of said central disc in a mounting configuration of said wheel rim on said portable tire changer apparatus; - driving means fixed to said supporting base and arranged to rotate said supporting means about said rotation axis; and - mounting means comprising an arm, movable and having a first end fixed to said supporting base and a second end movable, and an introducer element fixed to said second end, made of non-metallic material, in particular plastic, and configured to abut said external annular edge of said wheel rim in a mounting procedure in order to allow inserting and mounting a tire on said wheel rim by rotating said supporting means.