Puzzling Chain Problem When Shifting
 

I have a road bike with 2002 Campy Chorus 10-speed components. For the last 10 years or so it's not had any problems with shifting--everything worked as it should.

A few months ago I replaced the chain with a new Campy 10-speed chain cut to the same number of links as the old chain. Immediately after replacing the chain, the bike started exhibiting a strange shifting issue that I can't figure out.

Whenever I'm in the small chain ring up front and shift the rear more than a single cog at a time, going in either direction, the chain comes off the front chain ring and drops onto the bottom bracket. This, of course, requires stopping and putting the chain back on. If this happened once in a blue moon it wouldn't be so bad, but it's happening 3-4 times on every ride and it's getting to be a PITA.

I have the front and rear derailleurs adjusted properly. In fact, I didn't change the adjustments at all after I replaced the chain and the bike shifted perfectly before the chain replacement and never threw the chain. I removed the chain and checked for sticky links and obvious damage, but didn't find any.

Anyone have any ideas what may be causing this? This one is driving me crazy!

New chains are less flexible than older ones. They also have sharp edges on plates, and may be a bit stiff because of dried lube.

When you shift the rear it sends a wave don the chain similar to what you do when you try to flip a rope or garden hose over something snagging it. So combine the wave with the added stiffness and it can flip the chain to the tops of the teeth, and then over the side. The worn tooth profile on the ring can also contribute because there's some pitch error (what causing skipping on rear sprockets) so the chain is more likely to climb out.

Odds are the problem will disappear with some break in, and I'd give that a chance, maybe trying some better chain lube.

If it doesn't break in, you can use a file on the outer (toward the large ring) bevel of the teeth to move the point inboard more. Unless you're familiar with how bevel affects chain pickup and how to modify to advantge, I'd save this option for a last resort, and get more details about how it's done if/when it becomes necessary.

I have a bike that exhibits this behavior, but only on a rapid upshift. As the deraiiler arm kicks forward, it will sometimes come off the ring upfront. I wanted to get a chain keeper but its a folder and fitting one is expensive..I just try and remember to slow down my shifting.

Have you ever replaced the chainring?

My thoughts too. Depending on milage/weather, they could be pretty worn.

I wonder, also, if the rear mech is losing tension when shixting, so letting they chain go momentarily loose?

My single chainring is NOS Biopace....The OPs drive train is campy chorus, approx. 10 years old.