Ever seen this?

[j beede]

When I shift onto the small front ring occasionally the chain rides on the tips of the teeth and doesn't want to drop down and engage the sprocket normally. It does this on the bench and also on the road. Ideas?
...j

[cyclerUK]

I have had this a few times. It's one of those things that you wouldn't think can happen but obviously does. I just "fiddled" with the setting of the front derailleur until it stops doing it. A small adjustment of the cable or a small twist in the position of the derailleur may help.

Also check the derailleur height is O.K. Have you changed your chain lately? Not that this may be the cause, just asking.

[j beede]

The derailleur is set low, I used a thin washer as a spacer to set it above the largest ring. It is parallel to the rings--no toe in, no toe out. Chain is Dura-Ace and appears new. I will measure it for stretch today. I guess my chain rings must be very flat... it seems that any axial wobble would make the chain drop down to where it should be. Maybe I should put a little bend in the small ring

[Jordan300]

Is the chain hitting the front derailer at all when this happens? I think you just need to tighten or loosen your barrel adjuster 1/2 turn or so. But if not, your chain might be too stretched out. Maybe time for a new chain. Let us know what you find out.

[jr14]

Check your chainrings first. If they look like shark's teeth, they're worn and you probably need new chainrings. If the chainrings look good, check the chain for wear.
http://bikeride.com/chain-wear/
If the chain is good, start adjusting the front derailleur
http://bikeride.com/adjust-front-derailer/

All your answers in one place!

[j beede]

Let me try to better describe the situation... when shifting form middle to small ring the chain some times rides on the tips of the teeth of the small ring, not engaging in the usual way. It appears that gap between the chain's rollers and sideplates is centered on the tooth--the chain seems willing to go round-and-round this way. The FSA chain rings show no wear, no distortion. The chain is Dura Ace chain measures exactly 12 inches across 12 links using a steel rule with 1/64" increments. Setting H and L for the front derailleur is easy enough. Setting the cable tension is another matter. Any clever tricks to use there?
...j

[cyclerUK]

Is there a cable adjuster on the downtube?
Something like these:-
http://www.sjscycles.co.uk/product-Shimano-Shimano-Alloy-Braze-On-Down-Tube-Cable-Stops-with-Barrel-Adjusters-5511.htm

You should have one somewhere, maybe an inline one?

[jr14]

First, is this a road bike or mountain bike? Yes, I know Dura Ace is for road bikes, but some people used a Dura Ace chain on their mountain bikes back in the day. The reason I ask, is the chain might be JUST too narrow for your mountain bike's drivetrain. Try measuring the width of the links and then the width of the chainring. Hell, you should do that even if it is a road bike.

If it is a road bike, look for the cable adjuster like cyclerUK pointed out, and try shifting while adjusting cable tension a quarter turn at a time. It doesn't take much on the barrel adjusters to make a difference.

[j beede]

Road bike with FSA Gossamer triple crank and 105 front derailleur, Ultegra triple shifter. Yes, down-tube mounted barrel adjusters. Dura Ace chain measures "as new". It is easy enough to get H and L set. I do not know the theory behind setting cable tension for the front derailleur. For the rear I tighten the cable until it shifts from the 10th cog to 9th cog on the first click. That seems to work well. Shifting up and down works okay (but nothing like the rear obviously). The problem is periodically the middle to small ring shift leaves the chain riding up on the teeth tips. I will loosen the cable a bit to get a little more derailleur movement toward the bottom bracket shell. I have had issues with overshifting the small ring, but I will depend on the "L" setting to protect against that.
...j

[jr14]

(01-17-2010, 01:55 PM)j beede Wrote:  The problem is periodically the middle to small ring shift leaves the chain riding up on the teeth tips. I will loosen the cable a bit to get a little more derailleur movement toward the bottom bracket shell. I have had issues with overshifting the small ring, but I will depend on the "L" setting to protect against that.
...j

Right. I would do exactly that. You shouldn't have an overshifting problem that can't be solved with the limit screw. Try exactly what you said.

[j beede]

Anyone have know any smart ways to set the front derailleur angle? Do you suggest a little toe in or toe out?
...j

[jr14]

If you HAVE to, set it with a LITTLE toe in. That might help your shifting problem, but I doubt it. The derailleur should be inline with the rest of your drivetrain. Give it a whirl though, sometimes weird things do work.

[cyclerUK]

To much "toe in" and the crank arm may catch the back edge of the cage when on the big ring.
Be careful!

I would just slacken the the adjuster to start with. ( and use the LO screw to stop the chain going off)
If you go to far though, you might not be able to get the big ring.