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Join Date: Aug 2010
Location: Madison, WI
Posts: 11,199
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
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If the cranks you are looking at are 130/74 bolt circle diameter, you might not get the gearing as low as you want, a 110/74 is a bit rare but they exist and the middle ring could go as small as 34. The five arm 74 bolt circle diameter will fit a 24, but nothing smaller.
My two derailleur touring bikes have a 24T granny gear, that with a 32T biggest sprocket in back gives me a lowest gear of 20.7 gear inches with a 700c wheel. That gets me up plenty of hills.
You could run a 9 speed crankset but keep your rear cassette at 8, thus not changing your 8 speed shifter. My derailleur touring bikes are both 8 speed, but one of them has a 10 speed crank. The crankset does not have to be an 8 speed one.
There is nothing wrong with square taper, all of my bikes except my road bike are square taper. Assuming your 520 is square taper, it might make sense to stick with it. If the new crankset is designed differently you might need a different bottom bracket to have correct chainline.
My most expensive bike, when I built it up I saw no reason to spend a lot on a blingy shiny crankset, bought one on Amazon for $35 and that was seven years ago, that bike is still working great with a cheap crankset. Do not worry about getting a lower end crankset.