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The maximum RD wrap depends on the chain stay length, the largest spocket pnd the chain ring size chosen. A 40/46 uses 21.5 inches of chain, while a 38/46 uses 21 inches. A 16 inch, or 406.4 mm chain stay uses 32 inches of chain. The next even number is 16.5 inch or 419 mm.
The point is that some combinations may leave the chain slack in the smallest combination, in order to wrap the big/big, while others can make use of every inch. Chain length can only be changed in 1 inch increments.
RDs always have some excess wrap capacity to account for less than ideal chain ring and sprocket combinations.
My 46/44 big/big uses 22.5 inches of chain and the 415 mm chain stays use an odd 32.68 inches of chain. Adding 1inch for the 2x RD, the total is 56.18 inches, so a 57 inch chain is needed. It doesn't make full use of the 57 inch length.
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