Originally Posted by
tfg111
Nice Tread,
I am have the same problem, my chain is jumping under load some times. I am going to measure the chain. I also need to look at the cassette to see if it is wore. It only seems to happen in the middle gears.
This is a sign that your cassette is worn. The reason it's jumping only in those gears is that those are the ones that are worn the most. If the chain you're using is new, just ride for a couple weeks and the problem may go away.
When you replace your cassette, be sure to replace the chain too.