i have one of those bikes , they were built with the cheapest of cheap parts .
even the bearings on the front wheel are grinding ( total junk )
and up here its almost impossible to get the darn tire for it now .
your probably better off getting a set half decent 20 inch bmx rims and tires .
or see if a regular 24 inch will fit in ( mabey with the smaller rubber it might just go in .