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B-Tension Adjustment
From WikiPedalia
Shimano terminology for the screw that regulates the tension of the upper-pivot spring of a rear derailer. It should be adjusted with the bicycle in its lowest gear. Loosening this screw allows the jockey pulley to swing up closer to the cluster, improving shifting.
If the B-tension is too loose, however, the jockey pulley will bump into the largest rear sprocket, causing noisy running and possible shifting problems.
See my article on Derailer Adjustment for more information on this and other derailer adjustments.
