Trouble with front derailleur

Derailleur height adjustment is limited by the big chainring. The derailleur cage should clear it by about 2mm.

The derailleur angle is critical too. I generally get best results with the outer cage plate exactly parallel to the big chairing. If it's splayed outward a bit it takes more derailleur movement to access the small ring and that may cause it to overshoot.

Strangly, a too tight high limit screw can even cause a problem. It can cause the derailleur to hang up and, when it eventually releases the derailleur, it shifts too hard so the chain's momentum carries it over the small ring.

If all else fails, a "Jump Stop" or "Chain Watcher" can be installed to keep the chain from overshooting the small ring. They're about $10.00 US.

Retro Grouch said:

If all else fails, a "Jump Stop" or "Chain Watcher" can be installed to keep the chain from overshooting the small ring. They're about $10.00 US.

As I recently discovered, modern frames with beefy BB don't accommodate these dog fangs.

jimmiejams said:

I recently had my cranks swapped by my LBS from a 50/36 to a 50/34. I've ridden a couple of times since then, and at least once every ride, when switching to the small chainring, the chain comes off on the inside. And today, the chain didn't come off, but sort of "skated" across the top of the small chainring e.g. the teeth didn't slot into the gaps in the chain. No problem, I thought, I'll just adjust the low limit screw on the front derailleur and I'll be fine. The thing is, I found out it's already just barely throwing the chain over from the big to the small: if I tighten it even by a quarter-turn, the chain starts rubbing on the front derailleur when I'm in the small ring (and the big cog on the back). Does anyone know what else I can try? I'm not all that keen on having the chain rub all the time. Is it a height adjustment on the front derailleur I should be doing, since it's changed to a slightly smaller inner chainring (I guess not). Oh, this is Shimano 105 10-speed, 07 model. I've used these cranks before (FSA SL-K) on another bike with no problems.

Are you, by chance, using an 8-or-9-speed chain?!?

Did YOU or the LBS change the chain for some reason?

With a Shimano drivetrain, the front derailleur CAGE WIDTH must match the CHAIN WIDTH, and vice-versa, for optimal shifting ... more so with a triple than with a 130BCD double.

And, although Shimano says that you can use their "double" front derailleur with their compact crankset (vs. the FSA which you are using ... this is more a matter of the chainrings), you are always (IMO) better off using a triple-capable front derailleur with a "compact" crank ... I'm mentioning THIS because you should probably pony up for a new front derailleur AND you will be happier with the xx03 Shimano front derailleur than the xx00 Shimano front derailleur.

With a Shimano STI shifter, you can sometimes get away with a slightly narrower chain on a double IF you have a triple-capable front shifter that will give you a "third" indexing click BUT with the STI shifting you are always better off matching the chain width & front derailleur cage width.

alfeng said:

Are you, by chance, using an 8-or-9-speed chain?!?

Did YOU or the LBS change the chain for some reason?

With a Shimano drivetrain, the front derailleur CAGE WIDTH must match the CHAIN WIDTH, and vice-versa, for optimal shifting ... more so with a triple than with a 130BCD double.

And, although Shimano says that you can use their "double" front derailleur with their compact crankset (vs. the FSA which you are using ... this is more a matter of the chainrings), you are always (IMO) better off using a triple-capable front derailleur with a "compact" crank ... I'm mentioning THIS because you should probably pony up for a new front derailleur AND you will be happier with the xx03 Shimano front derailleur than the xx00 Shimano front derailleur.

With a Shimano STI shifter, you can sometimes get away with a slightly narrower chain on a double IF you have a triple-capable front shifter that will give you a "third" indexing click BUT with the STI shifting you are always better off matching the chain width & front derailleur cage width.

In adition to the above, I suggest you check with FSA, some of the early 10 speed cranksets has 10 speed rings on a 9 speed spider, resulting in the wrong spacing between the chainrings. :eek:

My policy is to go ALL SHIMANO when going 10 speed! 😉