DougG

The only time I've dropped a chain before was when shifting from the middle to inner of a troublesome triple, and that went away with proper derailleur adjustment. This time, I was on my newer compact double bike when it dropped off the inside.

The only thing is, I was not shifting at the time (or at least not in front -- can't recall if I'd just shifted the rear). The only factor I could come up with is that I'd been riding on the big ring all day, but at this time I'd forgotten that I'd shifted to the small ring to go up a hill, followed by some slow riding through a neighborhood.

So when this happened, we were speeding back up going out of town and I had shifted all the way to the small cog in the rear, which I normally wouldn't do on the small ring due to the cross-chaining situation. So would cross-chaining like this make it prone to drop off? At first thought it wouldn't seem so since the cross-chain position would seem to be biasing the chain toward the outside, not the inside.

Any ideas, or was it just one of those things? The bike only has a few 100 miles on it, so nothing abnormally worn either.

10 Wheels

It happens when you cross chain or forget what cogs and chain rings you are in

The Answer:
https://www.jensonusa.com/store/sub/1...0&pricemax=200

DougG

Yeah, I was riding without my Flightdeck cycle computer, which has a readout showing what gear you're in. With my "senior" memory, a good idea!

10 Wheels

I have them on both of my bikes......never dropped another one.

ftwelder

I have a new compact drive system. I also had severe chain-suck several times yesterday. I hope a good cleaning will resolve the issue.

Monoborracho

IMHO...if you dropped a chain on a compact, you front D/R stop isn't where it should be or your rear D/R is the wrong cage and won't wrap enough chain for your gearing combo, allowing a bunch of slop in the chain tension.

George

+1

oldster

if i am in small in back and go from small front(of 2)to big front the cross chain will cause front to go "past" big ring and off,,twicebefore I realized why...

Retro Grouch 

OK. When your bike is in the little/little combination do you get any chain noise from the front derailleur/chainring area?

If you do, I'm going to guess "operator error". Compact doubles, when they're in the little/little combination, have a tendency for the chain to rub against the inside of the big chainring. My guess is that your big ring tried unsucccessfully to pick up the chain and, when it failed, created slack that caused the chain to bounce over the little ring.

If it was my bike I don't think that I'd do anything right now but, if it happens again, I'd install the chain keeper that 10 wheels suggested.

John E

Is your front derailleur control indexed? Chain drop and cage feathering are strong arguments in favor of old school analog/linear cage control in front. Otherwise, check chain tension, chain condition (rollers should turn freely and elongation must be <0.5%, or 1/16" per 24 half-links), and chainring tooth erosion.

stapfam

Check the chain for tight links. Don't know if you fitted a new chain or not but it is normally a new chain on worn chainrings or cassette that would cause the chain to jump.However a few years ago I had a new chain on new chainrings and I had severe chain suck in granny. This was offroad and we put it down to Mud causing the suck. End of ride and cleaned everything up and we had one tight link that was the problem.

Same with the OPs problem. Mates bike and the chain was jumping a lot as it went over the rear cassette and it was down to a tight link. The amount the chain was jumping I could see that it could have jumped off the chain set. It didn't but worth checking.

Looigi

In my experience, compact doubles will drop the chain on the inside pretty regularly. There is a big gap between the cage and the inner ring. If the FD moves freely and there is little drag in the cables, it'll drop down smartly and can throw the chain if there is the slightest slack in the top run of the chain. A chain catcher like a K-edge or Dog Fang solves the problem.

BluesDawg

I had a problem for a while with the chain occasionally dropping off the inside when I would shift to my 34 ring. I was thinking of getting a K-edge chain catcher, but I did some fine tuning with the limit screw and have had no further incidents. I just had to find that magic spot where the derailleur would allow the chain to run cleanly in lowest gear but would not push it far enough to pass the small ring and drop.

ftwelder

All the parts on my bike are pretty new. We have had a lot of rain and I may have lubed a chain that was still full of water. I then picked up a ton of sand and started having issues. I checked the position of the front derailleur and reset the stops after a good cleaning. It seems to be good now. I also went to a dry wax type lube.

Wogster

The best way to fix this, needs a repair stand, you shift onto the lowest gear, then while turning the pedals you watch the derailleur, you should see it move slightly, turn it so it moves toward the pedal, one half turn, from the starting position. That should fix it, the problem with the front shifting is that it's on the high tension side of the chain, and that means it takes more to get it to shift, but once it goes, it will tend to go further then intended.

BluesDawg

huh?
https://www.parktool.com/blog/repair-...ur-adjustments
Look halfway down the page for "Front Derailleur - Adjusting L-screw".

DougG

Bingo! That's why I normally never ride in that combo, and when riding alone (the usual situation) I can clearly hear it and it reminds me that I should be on the big ring. But that day, I was riding and talking and had forgotten that I was on the small ring.

By the way, this is a carbon-frame bike with a non-round seat tube, so I'm not sure what chain keeper would work. I do have one on my conventional aluminum-frame triple.