Rear Der. question

[oldguy00]

The 'b-angle' adjustment screw, when should it be adjusted?? What does it accomplish?
thx!

[Dave]

The idea is to keep the upper pulley on the RD close to the largest cog for quick shifting, but the pulley should never touch the rear sprocket teeth or it will chew up the pulley and make noise.

[BdaGhisallo]

That's basically it. Think of the RD moving across and down to shift through the cassette. While the first cog of most cassettes is either an 11 or 12, it's easy to figure where the RD pulley should be so that it's close to the cog, but not touching it. At the other end of the cassette it's a different story. That last cog could be anywhere from a 21 to a 28. If the RD couldn't have its height adjusted, one of those final cogs would be way out of whack with what the derr would be optmized for. The B screw adjustment allows you to change the height of the RD cage so that you can compensate for the size cogs you have at the end of your cassette, while maximizing the shifting by getting that derr pulley as close as you can to all the cogs on average.

[SoCalSteve]

That's basically it. Think of the RD moving across and down to shift through the cassette. While the first cog of most cassettes is either an 11 or 12, it's easy to figure where the RD pulley should be so that it's close to the cog, but not touching it. At the other end of the cassette it's a different story. That last cog could be anywhere from a 21 to a 28. If the RD couldn't have its height adjusted, one of those final cogs would be way out of whack with what the derr would be optmized for. The B screw adjustment allows you to change the height of the RD cage so that you can compensate for the size cogs you have at the end of your cassette, while maximizing the shifting by getting that derr pulley as close as you can to all the cogs on average.

Thank you for such a GREAT explanation!

Steve

[Elefantino]

Good visual splainin' here. (http://www.parktool.com/repair/readhowto.asp?id=64) Scroll down.