I want to add drops to my R20, and I have a Sachs 3x7 rear hub. Will SunTour bar-end shifters work, I have a flat bar with grip shifters now and it works, but was trying to see if drops would gives me more comfort and possibily more speed.
Surly World Troller, Dahon Boardwalk, Raleigh 20, and the frame of a Surly Longhaul Trucker
I don't have experience with those specific components, but from what I know of IGH's you will not be able to use a bar-end shifter for the hub part of your 3X7 unless it is indexed specifically for a Sachs 3-speed hub, and I don't know if there is such a thing. The 7 cogs will not be a problem, I expect, as long as your shifters are friction or are indexed to the gear cluster. But you cannot friction shift a 3-speed hub. Or, rather, you can, but it's better not to: better for your hub and better for ease of use.
Also, I beleive Sram hubs maintain the same shifting as they did when they were Sachs, so you may get away with a Sram shifter. I would assume, but could easily be wrong, that the indexing for the hub portion of a 3X7 is exactly the same the indexing for a standard 3-speed hub.
If the suntour bar end shifter are shimano STI compactable it should work ok. However you will need a way of holding the rear cable in place to the internal and holding the outer cable still as the inner moves through it. You can just the clip that I managed some from an old LBS. I have converted 3 folders like this. 2 mezzos(3X9sram) and one space genie(3X7sach). Cable retainer clip visable on rear chain stay,You can also DIY something I guess