No matter how much I adjust it the chain skips off the cassette a notch or two when under power going uphill.

Work cassette, worn chain or both?

It didn’t seem to happen with the previous frame though, a few weeks ago. Frame flex?

In my experience, by the time that the chain starts skipping under load, you need to replace both the chain and the cassette, pretty sharpish before it starts wearing the chainring too.

what make of chain is it? If wipperman connex try flipping the powerlink upside down

chain, cassette, rings, jockey wheels etc – could be any or all off

In my experience, by the time that the chain starts skipping under load, you need to replace both the chain and the cassette, pretty sharpish before it starts wearing the chainring too.

+1

Just had the same, couldn’t stand to climb good practice for a while. Got away with a new chain only, which was at least 3500km old.

had the same thing using a new chain and cassette, turned out i had a weak/split link in my chain!

what make of chain is it? If wipperman connex try flipping the powerlink upside down

^^this^^

Happened to me with a new chain sprocket – who knew the quick links were directional ??

Thanks STW.

Had the same on mine for a few weeks. turned out the derailleur spring no longer had any strength it it. New derailleur and jobs a good un.

Most likely to be the chain and cassette that are worn , could be jockey wheels and/or chainrings as mentioned above.
But, it could also be a knackered freehub. Shimano type freehubs can get contaminated and result in the pawls not engaging everytime, especially under load.

Could be time to buy a chain checker.
Also worth checking rear mech hangar and mech for straightness, rear hub for not being broken, chain for not having issues and chainring teeth and sprocket teeth for being straight.

In my experience once that happened, I ended up changing the middle chain ring, the cassette and the chain.

There was clear wear on the chain ring though. It looked like a Chinese throwing star, due to dubious maintenance (ahem)

had this with my last chain brand new skipping under load tried loads things took it off in the end and cleaned up when inpected the plates and the rollers were really pitted/poorly made brand new clarks chain bag of sh*te ended up buying shimano chain 😕

Had similar thing a couple of weeks ago. Evans said not sure but you should probably buy a new cassette. Went home unconvinced and gave everything a very good scrub. Problem disappeared since!

does it happen on every sprocket of the cassette?

Usually in 1 or 2 , when putting the power down to get up a hill but only in the middle ring. Doesn’t seem to happen in granny.

Just looked at it, it looks well worn.

New cassette and chain bought.

May just be a stiff link in the chain. I had one that only skipped when I’d ridden through a puddle; the change in temperature was just enough to make it sticky. Happens more in smaller sprockets because the angle the chain runs through the derailleur and onto the sprocket is more acute.

You’ll need a new ring or two as well.