Originally Posted by
HTupolev
Most modern derailleurs don't need to be "fed" with very much chain, and some can move to get completely out of the chain's way.
The Stumpy I posted above, with 475mm chainstays, uses exactly one 116-link chain and has a 32-tooth big cog and a 48-tooth big chainring. Your 50-17 is 13 wrap lower than my 48-32, which means physically that about 6.5 fewer links need to be on the cogs. That 6.5 fewer links are 3.25 fewer links on each of the top and bottom runs of the chain, which is 1.625 inches or about 41mm. If you add 41mm to my chainstay length, you get 516mm, a bit longer than your 20" (508mm). So according to your chain and chainstay length claims, your drivetrain actually seems to require more chain than the math predicts when compared with my derailleur drivetrain. (Perhaps this is because of how you're adjusting the eccentric.)
We'll, just holding a long cage Alivio in my hand, I counted 9 inches or about 17-18 link pins. According to your own math that would be about 4 to 4.5 inches of chainstay length now allowed. Considering the average chainstay is about 16-ish inches long, that tracks close enough. The eccentric is a Bushnell & the adjustment range is about 1 inch as well.
How much is skewed on account of the Absolute Black chainring, I can not say.
You are welcome to come see the bike & my shop if you so desire. You in the PNW?
Here is me on said bike.