Normally, on any rear derailleur you are going to have your two limit screws. Generally, on most modern Shimano derailleurs with a low normal, or high normal. High gear screw is the upper one, and low gear screw is the lower one. You still have the B-Screw Adjustments, which adjustd how close the upper jockey wheel stays to the cogs.
Cable tension adjustment is completely different, if you increase the tension on the cable on a low normal derailleur, that means that it's going to shift quicker to a higher gear, and normally when we increase the cable tension, it moves the derailleur towards a lower gear, toward a larger cog. So that's a very significant difference, and it means that you have to think about it completely differently, just as when you, when you are riding the bike on a Shimano Dual Control lever, it's like a road lever, because the brake lever and the shift lever are now one. There is a front shifter, pulling cables it goes like that, releasing, it goes like that.
There is also an optional thumb lever that comes initially with it, and the thumb lever just removes really easily, I am going to go again to the middle, middle chainring, this is usually the simplest way to adjust it.
The standard rear derailleur, if your cable tension is right, it's generally going to prevent the chain from going into the drop out. If it's adjusted right, as soon as you pull some cable tension, it's going to move one cog, and if you had it so loose then it could go into here, then it wouldn't make that shift. But it's imperative to get it right on a low normal rear derailleur like this, because in this case, when you pull cable tension, you are driving the rear derailleur this way, and you are driving it right into that drop out, if you don't have this high gear limit screw right.
So it is a fine adjustment, so this is way extreme, but if I go to two turns, you can see how it's just want to go right straight into that drop out. And of course, you want to make sure that it does go down, so if I tighten this say half a turn, it's still dropping down. So you want to make the limits screw loose enough that it makes the shift easily, you're not really having to push against the limit screw a lot, but definitely that it does stop the movement.
So now going back the other way, normal derailleurs you have to be really worried with the limit screw, because you don't throw it in the spokes, but if you have your cable tension adjusted right on a low normal, even if you had your low gear limit screw backed all the way out, it wouldn't go into the spokes, because you are just releasing cable to get it there, and if you have it adjusted right, when you push it ones it drops down this way, then it's not going to go on the spokes. We'll go ahead and tighten this limit screw down, and you will see how you can stop it. Now I release cable, I know, it won't go up there.
Now we are going to talk about, B-Screw Adjustments, what you want to do, is have that upper jockey wheel close to the cog, but not too close. If we are loosen this screw, it's going to allow the derailleur to pivot forward. Now you can see that bouncing, see have that upper jockey wheel is bouncing up and down, because it is pinching the chain between the jockey wheel and the cog. So you can really notice that when I am pedaling backwards, when I am pedaling forward I can feel it a little bit, but it's not too bad. In any case I don't want that, that bumping so I am going to just tighten it a bit, so I can eliminate that bumping.
You always have some bigger space on the smaller cogs, and particularly, when you are in the big chainring, this is about the best compromise you can get.
