There are no gears that will make a 30% grade "easier." If you're built like a world tour rider, 30% would require +500W to manage 5mph. The rest of us would more than likely have to get off and walk.
I don't know where people live where these insane, virtually impassable grades exist in number. I have one paved road in a 20 mile radius that exceeds 20%, and it's an access road to a reservoir, closed to traffic, reached only by lifting a bike over a fence. It's that steep for about 60 yards.
If you have any questions about more realistic conditions, we may be able to offer some suggestions.
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