My chain keeps shipping off the side of the lower jockeywheel on my winter bike

Had it once before, and the jockeywheels looked worn so I replaced them: now it’s back a few hundred miles later.

Drivetrain is clean, hanger looks ok, indexing is fine, but the chain runs up off the lower jockeywheel and fouls the side of the cage.

Any thoughts?

I my experience its almost always a twisted hanger and with modern stuff with short chainstays it needs to be less than you think.

Get into a decent bikeshop with a hanger alignement gauge rather than eyeing it with some adjustables.

Seconded. I’ve had the same but remedied it with a spare mech I had.

If the hanger is bent, DO NOT just bend it back, replace it. They are very brittle indeed and you don’t want a snap at speed.

I was thinking along those lines…

Cheers guys