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How to Adjust a Bicycle B-Screw

Learn how to adjust a bike b-screw from Silk Road Cycles' Brendon Nicholas in this Howcast bicycle repair and maintenance video, part three of three.


Shift it all the way down to the highest gear. Now it's in cross gears right now. You don't want to ride in cross gears at all. Basically that means the chain is flexed from one side to the complete other side.

So we'll shift up into the highest gear to see if our cable worked right. It worked right.

Now you want to make sure you're adjusting the high limit screw. So if I adjust it too much, again, it's going to rub and make a lot of noise. If I adjust it too little, then when I go to shift to the highest gear. Doesn't work. Let's see. So if I adjust it too little then when I go from the low gear to the high gear, it has the potential to fall off. Which this one is not doing at all. There we go.

So if I adjust it improperly, and I go from the smallest gear to the highest gear, then it has the potential of falling all the way off. So you want to make sure that that is adjusted properly so it will prevent it from doing that.

Great. Now that your lowest gear here, the largest cog, the limit screw is adjusted, you want to adjust your B screw. So basically what that is, is it's pushing against your derailleur hanger, it basically sits right on the derailleur hanger and it pushes your derailleur, like that, basically.

So the purpose of this is that you can put different sized cogs according to whatever the manufacturer specifications are. So to adjust the B screw using a phillips head and you tighten it to make your derailleur go out, like that. Loosen it to go down. And basically, what you want to have is, from this jockey wheel right here, this small little plastic cog, should be about two to three millimeters away from the teeth of the largest cog or the lowest gear.

So if your B screw is too tight, basically it's going to have your jockey wheel, your highest jockey wheel here too far away from the largest cog. That's what it's looking like right here.

Now, if it's too loose, what's going to happen is the jockey wheel, is gonna, these metal, these plastic teeth here, are going to hit against the metal teeth and make a lot of sound. And t's also not going to shift as well.

So when you're adjusting the screw, you want to make sure that your jockey wheel teeth are the proper specification away from the largest cog here, the teeth, so they're not hitting and also so they're not too far apart. Most manufacturers tell you it's usually around two or three millimeters between the plastic teeth and the metal teeth.

So that's how to adjust your derailleurs and keep your chain running smoothly.

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