I'm having this problem with chain suck on my road bike.
After it happened the first time, i set the derailleur limit screws in an attempt to prevent it.
I have a triple with a 9-speed setup and I even left the setting so that when the chain is on the granny and on the large ring on the back there is a slight rub on the FD.
As I was riding today, I tried to trim from the middle ring but it went to the granny. The weird thing is that the chain didn't fall of here. I then shifted so that the chain would go to the middle chainring, this is when the chain popped off and went to the BB shell.
What could be causing this?
Everything about the shifting is satisfactory but this.
Thanks for your help!
I'm just fortunate that the cranks didn't lock when going fast.
the chain lodged between the granny and chainstay and had to use a stick to push the chain back out (didn't want grease on fingers)
might have to take to the LBS for adjustment
My touring bike has a tendency to do that. The problem I have is in the shifter and there is nothing that can be done to fix it. The shifter is of the type when you press the shift lever to cause a down shift it releases a pawl allowing the FD spring to pull the cable and shifter pawl to drop to the next notch. When it does this the FD can cause the chain to be thrown too far bypassing the chain ring it's supposed to engage. Having a cable with a little drag to slow down the FD on downshifts would solve the problem but then you create a problem when up shifting to the next higher chain ring due to the required extra effort to overcome the cable drag. I installed a Third EyeŽ ChainWatcher which clamps around the seat tube. It prevents the chain from dropping from the smallest chain ring to the BB so at least the chain will stay on the chain rings.
Down tube or bar-end type shifters would fix the problem as your not allowing the FD to snap the chain over for a down shift where modern STI and dual lever thumb shifters allow that to happen.