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cyclotron3k
Yes, it's plenty. Let's give them the benefit of the doubt and say the pitch circle really is a circle but with its centre 0.3mm away from the centre of the bore. If the chain is exactly the right length with the sprocket in it's most rearward position, then half a turn will free up just under 1.2mm of chain to flap about, and if you keep the upper run taut then the lower run can droop by about 15mm if you pull down in the middle of it
b=200mm
c=200.6mm (the original b plus half the spare chain length)
a²=c²-b²