I would think plenty, especially if the range of the nine gears is reasonably high. Road bike cassettes can be quite narrow range, eg 12-25, but mountain bike cassettes can be much wider, eg 11-40. Foldies tend to be in between but if the rear cassette is something like 11-28 or 11-32 then probably good enough. It is fairly easy to expand the range a little, and perfectly feasible to expand it a lot on most foldies.