Originally Posted by
Kopsis
Big-big+1" ... however ... if you think there's any chance you'll want to switch to a bigger chainring (42T or 44T) or bigger max cog you can add another couple inches and everything will still work fine. Your RD (even a short cage) probably has plenty of excess capacity on a 1x, so sizing a little long has no down-side and leaves a little room to grow.
Yup. Big/big +1 will give you the shortest chain that will safely work with that gear combination. The arm of your derailleur cage will be pulled almost horizontal when using your biggest rear cog.
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