what cranks do you have now? you need something smaller than a 39? I haven't seen your hills but I might be inclined to do more a triple thing maybe a 53(2)/39 and 30 or 28 granny, or you could use something slightly larger for the granny.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk