I have a 20x1.75" 6-speed folding bike with 52x14-28t drivetrain. Even with the gearing at 52x14, ~3.71 ratio, I can still pedal uphill.
I also have a 700x25C fixed gear with 49x17t gearing or ~2.88 ratio. I have yet to try riding it on uphills so I'm not sure if it's going to be difficult to pedal with that gearing.
I know that the gear inches depend on the ratio multiplied by the diameter of the wheels. Given that, I know that the gear inches of my folding bike is at around 74 while the fixed gear is at around 79. But which one actually determines how hard it is to pedal, the gear ratio or the gear inches? If it is the gear inches, would 5 inches higher be that significant? If it is, I'm thinking of getting an 18t or 19t cog.