increase highest upper ratio with gear hub I have a 20" folding bike with a shimano Nexus Inter-3 (most probably this one), and I find that even on flat terrain (not to mention downhill) the 3rd gear is simply too slow: I often find myself cranking very fast exerting a very low torque, and 2nd gear is good for most slopes (&lt;15%). I mainly use the bike for commuting, on mostly flat terrain.

My current top speed seems to be around 20-25 km/h, I would like to be able to do 40 km/h. That means an increase by a factor of two.

I am searching for a way to up the gear ratio, my options seem to be:


Increase the size of the front chainring (45 currently):


This would make folding harder.
I would also need to change the chain protector and possibly the pedals.

Decrease the size of the rear cog (18 currently):


This would increase the strain on the individual cogs and increase the chance of slipping (that already happened) and chain fall-off.

Change the gear hub to one with a higher upper ratio:


May need to change the shifter and corresponding wiring
May not fit in the current frame
The current ratio is 1.360, I would like at least 1.8 or even 2.0
I do not really need gears below 1.0, and certainly not below 0.73 (my current 1st gear). Unfortunately most gear hubs concentrate on the lower gear ratios, but I am yet to find a comprehensive table of available gear hubs (wikipedia's, and Sheldon Brown's have different flaws). Shimano's 4-speed hub seems promising, but is discontinued.



Which solution (or combination of them) do you recommend? If it is the third, what specific gear hub(s) do you recommend?
Decreasing the rear cog is by far the easiest of your options.  On road bikes, chain rings of 34-39 teeth and rear cogs of 11 are common, so you would be within range. The force on the chain is higher for smaller chain rings, not larger ones.  Slipping probably comes from not having the chain tight enough.  You may be able to move the rear axle aft to tighten it.