Originally Posted by
rydabent
The "B" screw if very important in how your bike shifts. It is probably the most misunderstood adj on the bike. Contrary to conventional wisdom it is NOT a chain "tension" screw.
The "B" screw needs to be adjusted for a clearance between the jockey wheel and the largest cog on the cassette. For instance the distance between the jockey wheel on my Sram 7 RD is stated to be 6mm. The best way to measure that clearance is with a 6mm allen wrench in my case. Adjusted to the proper clearance it will assure quick crisp shifts, and will not let the chain bind or jam between the largest cog and the jockey wheel.
I adjusted it for 2-3mm of clearance between the pulley tooth and largest cog tooth... I'm told that's the best distance, in general, to give it enough clearance but still allow the sharp torque on the chain required for quick shifting