chain suck explained…

Hi
I have just bought a new chain and as expected the jockey wheels are jumping,and riding up towards the frame when any pressure is placed on pedals.Am i right in thinking that this is “chain suck” ?
If so i am guessing this is caused by worn parts…can i get away with just changing the front chain rings,and leaving the old cassette(which doesn’t seem worn at all)??
Thanks in advance

as expected the jockey wheels are jumping,and riding up towards the frame

The jockey wheels are riding up towards the frame??

Chainsuck is when the chain catches on the granny ring (very occasionally the middle) and gets “sucked” up between the frame and the chainset.

So, yes, you can usually get away with just changing the chainrings.

when the chain gets sucked up as described by DezB, the jockey wheels have to move up to cater for the extra chain length needed to loop back round the rings!

however, yes, sometimes just chain rings needed

The best way i can describe it is..if you put a chain back on and you need some slack on the chain to link it onto a front chainring you can lever the hanger towards the frame (where your lizard skin would go)to give you some slack.This is the action the hanger is making when pressure is applied to pedals. I HOPE this makes sense 😯

That’s not chainsuck. Chainsuck is on the front (mostly middle ring TBh) where the worn chain and chainrings, and dirt combine to not release the chain early enough, it just wrapped up, and jammed between the chainset, and chain stays. Sounds to me that what you’re describing is that you’ve changed your chain, and it’s skipping on the cassette? It may not look it, but the cassette is probably too worn for the new chain.

Sounded more like stiff links to me.

Do the jockey wheels spin freely? I had a siezed jockey wheel on my road bike which made the rear mech do funny things when I freewheeled.

Sockpuppet is correct. What the OP is describing is a symptom of chain suck in that the chain is being sucked up by the chainrings but the cage of the mech is having to swing forwards and upwards to accomodate the effective shortening of the chain due to the suck.

Replacing the chainring that is sucking should sort this out for you.

Stiff links would do this all the time, not just under power.

Yeah thanks,Matthew H/SP Sounds like they have hit the nail on the head…the chain is new remember so no stiff links,and the rear mech is new too,so no sticking jockey wheels.

I would’ve thought the last thing you notice when you have chainsuck is the movement of the jockey wheels.
The jammed chain and the grinding of my chainstays always caught my attention!