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12-27-07, 05:26 PM
Is a b-screw something to be changed? Or is each one specific for each derailleur? I am a pretty fair common sense wrench, but I am having a little problem.
For the first time in a long time, I bought a new bike from an online dealer. It was last year's model and had been on the rack for awhile and therefore I got a great deal.
Facts: Shimano Dura-Ace throughout.
12/23 cassette
Medium cage derailleur
I switched to a 12/27 for a heavy climbing century and the fun begins. I couldn't figure out why I had so much resistance in the lowest gear. Usually, something as low as a 27 would give me tree climbing capability. I have some pretty fair sized quads and tend to mash a bit. I like the close ratios of the 12/23 for riding around where I live, and the 23 is low enough for the riding I do. I live north of atlanta on pretty hilly tererain. I checked the rear end, the derailleur pulley was almost dragging on the 27 gear. I checked the b-screw, it was useless. The derailleur was not mounted properly on it's detents, it looked like it was installed while the wheel and chain were under pressure. The b-screw didn't even line up with the frame stop.
I took the wheel off, put the derailleur on the frame properly and adjusted the b-screw all the way out. It seems just about 1/4" short of getting the derailleur really clear of the low gear. It is not touching, but it is definitely too close and causes some pretty extreme chain angles. I would feel better with a bit more clearance. Would it be counterproductive to get a slightly longer b-screw, or should I be experimenting w/chain length, screw or spring tension, etc? New ideas would be welcome. I don't really have a lot of faith in most of the shops around me. It's a good thing manufacturers only rely on them to put seats, wheels and handlebars on the bikes they build. I have seen some of you guys have some real experience, any old hand to help me out here?
For the first time in a long time, I bought a new bike from an online dealer. It was last year's model and had been on the rack for awhile and therefore I got a great deal.
Facts: Shimano Dura-Ace throughout.
12/23 cassette
Medium cage derailleur
I switched to a 12/27 for a heavy climbing century and the fun begins. I couldn't figure out why I had so much resistance in the lowest gear. Usually, something as low as a 27 would give me tree climbing capability. I have some pretty fair sized quads and tend to mash a bit. I like the close ratios of the 12/23 for riding around where I live, and the 23 is low enough for the riding I do. I live north of atlanta on pretty hilly tererain. I checked the rear end, the derailleur pulley was almost dragging on the 27 gear. I checked the b-screw, it was useless. The derailleur was not mounted properly on it's detents, it looked like it was installed while the wheel and chain were under pressure. The b-screw didn't even line up with the frame stop.
I took the wheel off, put the derailleur on the frame properly and adjusted the b-screw all the way out. It seems just about 1/4" short of getting the derailleur really clear of the low gear. It is not touching, but it is definitely too close and causes some pretty extreme chain angles. I would feel better with a bit more clearance. Would it be counterproductive to get a slightly longer b-screw, or should I be experimenting w/chain length, screw or spring tension, etc? New ideas would be welcome. I don't really have a lot of faith in most of the shops around me. It's a good thing manufacturers only rely on them to put seats, wheels and handlebars on the bikes they build. I have seen some of you guys have some real experience, any old hand to help me out here?