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Today I finished converting my folding bike from 1x9 to 3x9. The inner side of the front derailleur had a lip which was hitting the bottom of the mounting post. I was able to dremel enough away to get the full range of motion. That wouldn't be needed on a bike with an actual braze-on mounting tab.
The front chainring is 48-36-26, the rear is 11-32. My lowest gear gives me a 1.1 gain ratio (using Sheldon Brown's gear calculator). I'm using Shimano compatible components. This means that the amount of cable pull to change the front gears is different between road and mountain bikes. To be extra safe I used a Microshift front derailleur and flat bar shifters from their 9 speed road line.
It can be safely described as a flat bar folding road bike.
