Is my chainring worn? Chain dropping/slipping under high torque

Since around a week whenever I try to sprint uphill my chain slips/drops. I tried putting on a new chain but unfortunately that didn’t work

(Please ignore the disgusting floor and wall🤮, that’s work in progress )

I had a similar issue on a mtn bike. I found my rear derailleur was cracked.

I just reinstalled the rear derailleur and replaced and checked the hanger. They look good

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I’ve seen worse chain rings than that, but I do wonder if the 12sp systems are more sensitive to wear than their predecessors?

Is it slipping at the chainset end rather than at the cassette end?

That’s really hard to tell because making it slip requires quite an effort and now I know I also need to prepare for the slip else I will have an accident

I ask only as - generally - cassettes (or the most used sprockets on them) tend to wear more quickly than chainrings.

Do you recall if the slippage was on any particular sprocket(s)

But yes, if the chain is coming off the chainring, it could be down to wear, or a bent tooth, or just a front mech set up tweak, amongst other things.

More likely to slip at the cassette than chainring - work through the cassette putting down power (maybe dragging the brakes if needed) until it slips, then change gear and see if it does it again. If not, it’s a single sprocket on the cassette (which is usually the case).

If it’s doing it in different gears at the rear, try changing to a different chainring and repeat.

Only on then 10 tooth sprocket, which I seldom yae

With that additional info, I’d look at limit screws/trimming - but it is the smallest sprocket, so least potential engagement even in the best case scenario

Yes, as @alexgold123 says, if it is just on the 10 sprocket, it is worth checking the chain gap, limits and trimming on both front and rear mech. Could also be worth checking that the mech hanger is still straight too.

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New (and checked with dag 2.2) hanger

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Is this happening when in the big chainring or small chainring? Or both?

A chain will stretch over time and will deform the teeth on your cassette and chain ring.

The large chainring looks in need of replacement and if the cassette has similar wear you need to swap your cassette to. I can’t see enough of the teeth on the inner but what is visible looks like the inner is in need of replacement.

. A chain measuring tool will indicate wear, over .75% and you will need to replace the chain. Over 1% and you’ll need to swap the rear cassette. Not swapping the cassette in this situation could mean the new chain slips on certain cogs. If you get way with the chain not slipping you’ll wear out the new chain prematurely because the rear cassette is worn.

Dependent upon your maintenance regime and the conditions you cycle in, a ratio of 4 chains to one cassette is about normal.

It’s prob not his chain

I have the sram flat top chain measuring tool too and none of my 3 previous chains were in need of replacement according to the tool

I always respond to these kinds of posts because I’ve lived through the “worst case scenario” when it comes to chain slippage due to worn chainrings…

A few years ago, I went for a ride with a worn chainring and had recently replaced the chain. At the end of the ride, I was going to do a few sprints. On sprint #1, my chain jumped off of the front chainring, I got bucked over the bars, and the person I was riding with flipped over me and broke their collarbone. I messed up my hip and had to take about a month off from training to recover.

So I always recommend playing it safe and replacing the chainring if there is any doubt!!!


Edit to add: you can check to see if it’s the chainring causing issues relatively easily. It’s called the stomp test. Put the chain on the big ring and keep it on a pretty hard gear on the cassette. Align the cranks parallel to the ground. Grab your brakes so the bike won’t move, and stomp on the cranks (literally STOMP on them). If the chainring is worn, the chain will pop off.


I will try. Saturday I will do Marmotte and unfortunately the chainrings are out of stock until July. Fortunately in normal riding there are no problems and for a 177km grand fondo with 5km of climbing I don’t suspect I will do a lot of all out sprints or even use the big ring much


I snapped the rear gear cable on the TT bike before my race last Thursday it put the chain in a bad alignment and it was throwing the chain off the chainrings under high torque. I don’t think anything is worn and its just the alignment.

I don’t get why alignment suddenly would become an issue. Although I did change the derailleur hanger a few weeks ago the problems didn’t start right after and I didn’t touch my front derailleur.

Hopefully today I will receive the correct climbing cassette and can try the stomp test as @ZackeryWeimer suggested

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If you changed the rear derailleur hanger its almost certainly linked to that. It just takes a tiny bit of extra movement or even speed of it to throw a chain due to the alignment etc when it was just within tolerance before. Good luck in sorting it out.