Chain overshifts off outer chainring

> I swapped out 54/44 chainrings for 50/38. Followed Shimano
> specs when I lowered the shifter. After making the change
> the chain would repeatedly roll off the outer ring (i.e.
> going from small to large ring). When I increase the size
> of the middle ring to 40 problem goes away which
indicates
> I have the shifter adjusted OK.
>
> Anyone know if a 12 tooth change is too much or is a
> shifter that can
handle
> a 54 tooth ring too large for a 50 tooth ring?
>
> Also wondering if filing down one tooth on either or both
> rings might help the problem. Thought before I file I'd
> check to see if anyone had
thoughts
> on subject

Don't file the teeth; that's not going to help anything. My
guess is that the angle of the derailleur is off a bit. In
general, when you're in the large front/small rear combo,
the derailleur's outer cage plate should be just slightly
pointed out at the back (away from the chain & wheel). Not
much, just slightly. You might have it parallel or even
inboard a bit, requiring that the limit screw be moved out
further than it ought to be in able to get it to shift up.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

Thanks Mike I'll try that.

On the stand I notice that when the plate displaces the
chain enough to get it off the small ring, the chain is
actually past the outer ring. With the 40 tooth that doesn't
happen. Be interesting to see what changing the angle does.

Bob

"Mike Jacoubowsky" <[email protected]> wrote in message
news:[email protected]...
> I swapped out 54/44 chainrings for 50/38. Followed Shimano
> specs when I lowered the shifter. After making the change
> the chain would repeatedly roll off the outer ring (i.e.
> going from small to large ring). When I increase the size
> of the middle ring to 40 problem goes away which
indicates
> I have the shifter adjusted OK.
>
> Anyone know if a 12 tooth change is too much or is a
> shifter that can
handle
> a 54 tooth ring too large for a 50 tooth ring?
>
> Also wondering if filing down one tooth on either or both
> rings might help the problem. Thought before I file I'd
> check to see if anyone had
thoughts
> on subject

Don't file the teeth; that's not going to help anything. My
guess is that the angle of the derailleur is off a bit. In
general, when you're in the large front/small rear combo,
the derailleur's outer cage plate should be just slightly
pointed out at the back (away from the chain & wheel). Not
much, just slightly. You might have it parallel or even
inboard a bit, requiring that the limit screw be moved out
further than it ought to be in able to get it to shift up.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com