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so.
double shimano 130bcd, 73mm bb, square taper jis, chainring on outer position.
for 50mm chainline would need a 118mm bb? (46mm chainline - 110mm bb -> 50mm chainline 110+4+4mm = 118mm)
not sure though if the 130mm bcd crank will clear the wide mtb chainstays (genesis io) but ideally I want to be able to use my choice of 130mm chainrings (42/43/44) with a 16t rear. (might also go bolt on cog).
many thanks.
Rodolfo
Scilly.Suffolk
Assuming your cranks are Shimano standard, then the chainline measured between the two rings is 43.5mm and 46mm for the outer ring.
So in an ideal world you'd want a 105mm BB, but 107mm is probably as close as you'll get and will certainly be an improvement.