Rear derailleur: importance of the B-screw
 

Hi,

Adjusting a new derailleur, and wondering the importance of the B-screw...
How should I set it? have the upper jockey as close as possible to the bigger cog when on the granny in front without it being unsafe?
I read that ~6mm was a good number... is that correct?

My actual question is: how important and/or critical is that?
Will this affect my shifting speed/quality?

I tend to ride small cassettes (I mean with small large sprockets: 12-23 being my favorite) which means an optimal B-screw setting would lead to it being pretty extreme a setting...

Is it worth it? or should I leave a bit of an extra slack to allow switching to a little larger cassettes for when I am climbing (12-25 is my mountain cassette)?

Thanks!!

The B-screw sets the position of the upper pulley relative to the cassette. The closer the pulley is to the cassette, the better the chain can catch on the teeth and ramps on the cassette which will improve shift quality (faster engagement). If the pulley is too close, it will interfere with the movement of the derailleur when you shift to the bigger cogs.

Set the B-screw while on the largest cog just enough that the upper pulley leaves the cog at an angle (not parallel to the ground).

Yes. But most of the time, the factory setting of the B-screw is good enough for a lot of people.

As I've said, the default setting is good enough. I wouldn't adjust it if you're not having problems shifting to larger cogs. It's not that difficult to do though. You can readjust if and when you change cassettes.

Or you can adjust it for the 12-25. The change is small enough that it will not be that far from the 12-23 - unless you're OC about your shifting then do the former.

I find I like it as close as possible without catching. Makes for precise shifting. :)

Since the B screw is a no cost adjusting aspect of the gear system why doesn't the OP (or any one else) simply change it and then see what shifting performance changes happen. Then draw their own conclusions. Andy.

Good point...

Turn the crank very slowly and shift from the next to largest cog to the largest cog. As you shift, watch the chain between the top of the pulley and the bottom of the big cog. There needs to be enough room between the the top pulley and the teeth of the big cog for the chain to pass through as the shift is made. If there isn't you'll see and hear it as it forces its way between the two bumping the pulley, cage and RD .

Is what worth what?