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Or, in other words, What does the B-Tension screw do? If you’ve tried to adjust your own derailleur, chances are good that you’ve wondered the same things. But, since that odd ball screw tends to confuse a lot of people (more than one reader has asked essentially the same question), we thought it would be worth a closer look…

To make sure we weren’t missing anything, we reached out to one of the most knowledgeable people we know on the subject – Shimano’s Mountain Bike Product Manager, Nick Murdick. Simply put, the B-Tension screw is there to control the gap between guide pulley (the upper pulley on the derailleur) and the bottom of the cogs. Since this gap will always be most easily seen and tested by the relationship between the derailleur and the largest cog on the cassette, it’s recommended that you set your adjustment here. It’s also recommended that if you have a front derailleur, it should be shifted into the smallest chainring.

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