Originally Posted by jasong
What's the gear range for the folder? What speed did she have to maintain 100 rpms to keep up with you?
Even cheap bikes can maintain their rear wheel position, so maybe a nut is loose back there leading to chain slack.
Like a lot of the cheap bikes, replacing some of the crap components will actually make them fairly decent. Of course, sometimes that's almost impossible for weird sizes. 7 (or less) speed shifting bikes are pretty smooth compared to quirky 9/10 speed drive trains, except on all but the nicest components.
14T small rear, seems to be about a 40-44T ring. So that gives a top gear inch of no more than about 63.
A 53T big ring could bring it up to about 75 gear inches. Maybe replacing the rear freewheel with an 11/30 could bring it into the high nineties, but unless the rear is steel, spreading the dropouts would risk frame damage.