Why does my chain drop when already on inner ring??
 

I recently took off my rear wheel to change a flat tubular for the first time in like 5 years. When I put it back on,I started getting occasional chain skip and, more annoyingly, when I shifted from 50 outer to my 34 inner,the chain would not drop when shifting (I have the front deraileur inner limit screw almost rubbing the chain) but it slide ride off when I started pedaling..wtf?? I never had mechanical issues b4: HELP Please (Note: my bike had been sitting all winter-Shimano 10 sp Durace double)

Looking at some other posts, I may have a damaged chain, hence the skipping?

Check the chain hasn't come off one of the jockey wheels.

Inspect the chain for any damaged or bent links, or stiff links.

Check the FD cage position hasn't been knocked out of alignment.

Check the rear wheel is seated in the drop outs properly. Also check the cassette lock ring is tight. And do a bolt check on everything else. The crank, FD, chainring bolts, RD, cable clamps bolts etc.

How worn is the chain and inner chainring ? How many miles have they done ? Another possibilty could be chain suck. Google it if you dont know what is. Basically the chain does not release properly from the bottom of the chainring and causes it to come off the chainring. In a worst case scenaro it can cause your chain to wrap up, get entangled and get jam the drivetrain and damage the frame.

If it never skipped before, I'd replace the chain. Even if the cassette and chainrings are worn, you'll need a new chain. And if they need to be replaced the chain will tell you as it will not run smooth.

As for falling off (inside) my guess as already suggested is the derailleur needs adjustment. It could also be a cable that is too loose or bimding in the housing.

My son had an issue with the chain falling off on his mountain bike due a cable that was too loose and barely shifting up to the larger chainrings. It helped, but I still installed a chain catcher due to the rough terrain.

John