ppc

Agent B,

Don't spend any money on chain guards and other gizmos. These are devices that hide a malfunction in your derailleur setup, instead of correcting it. They're a patch on a wooden leg.

What you need to do is figure out what the problem is. Assuming you have adjusted the derailleur how it's supposed to be, there are several other things that could be happening. Try checking this:

- The BB spindle might be a bit too long or too short, and the derailleur doesn't quite work in its intended range, so two of the rings work good but the chain goes off the third. See if one of the stop screws is all the way out, "feel" if the derailleur has a hard time reaching one way or the other, forcing you to over-compensate in the adjustment.

- Check that the derailleur cable feeds in the intended groove on the derailleur arm, and not at the other side of the screw (I know, it's dumb, but everybody does dumb things once in a while).

- Check that the derailleur is as close as possible to the largest chainring when fully extended, *and* the collar is flat against the tube when you tighten it down. I had a front derailleur once that would sit a little crooked on the tube and wouldn't line up on its own, causing all sorts of grief. So now I almost tighten the collar, wiggle the deraiilleur up and down a bit to make sure it's installed flat, then tighten it fully.

If everything seems right to you, you can also try this: when the derailleur kicks the chain up to the largest ring, it's mostly the front/top of the cage that moves the chain, and when the derailleur kicks the chain down to the granny ring, it's the back/bottom of the cage that tends to do the work. Therefore, you have the option of favoring one behaviour over the other by angling the derailleur right or left. In your case, you have "too much kick down" so to speak, so you can try to angle the derailleur counter-clockwise slightly (i.e. the back of the cage moves outboard slightly) and readjust the derailleur. You might find your ideal setting this way.

You can also try to move the granny ring inboard a bit, with 0.1mm spacers.

Finally, as a last resort, you can try to bend the cage slightly. For example, you might want to spread it a bit at the rear, so the right face has a longer travel to touch the chain and kick it down. Or you can try to bend the back of the cage so the left face is more outboard, to help it keep the chain in check on the granny ring. The cage isn't that fragile, it won't mind too much if you don't overdo it, but I'd avoid playing with that until there's no other option.

Of course, it's entirely possible that your derailleur just doesn't want to live with your bike, and you might want to try other brand/models.

Good luck.