Troubleshoot: dropped chain while sprinting

Never been so happy to have done a workout indoors rather outdoors. So here is what happened:

I had Shasta on the calendar for today. The first four efforts at 200% were all good. The fifth not so much. Right into the sprint my chain dropped.
I enjoyed the Adrenaline while it lasted and put everything back together. I carefully tried it again with the same result. I afterwards went for some easy sweetspot and threshold. Chain stayed on.

Any ideas what could be causing this? Here is the workout

and a few pictures of the front and rear derailer.
For what it’s worth, I did put it off the turbo for a better picture.

I thought this was gonna be Peter Sagan… :rofl:

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It’s quite an experience. :joy: Glad I have done the intervals seated as per the recommendation.

As to the cause of the problem, it could be several factors…front derailleur adjustment being the most likely culprit. It could also be a worn chain, chainrings or cassette…or any combination of the 3.

In a worst case scenario, it could be a cracked frame, either on the chainstays or the BB area.

if you don’t do your own maintenance, take it to your LBS, tell them what happened and have them give it the once over.

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You dropped it outside the smallest cog? While shifting to it I presume?

First potential is the limit screw - since we don’t shift there very often, the limit screw can be off without being noticed. I assume shifting to all other cogs is fine?

Second is a bent hanger - this would also show in some erratic shifting through the cassette.

Third is a worn chain - you would get more skipping than the chain jumping off, however.

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I assume you’re using a “wheel on” trainer?

There’s so many possible causes. It would help for you to be as descriptive as possible as to what happened. i.e. gear you were using, if you were changing gears, dropped the chain off the front chainring of the cassette cog?

Just an aside, I thought it was kinda funny that you referred to 200% efforts as “sprints” and then I saw your username :grinning:

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A potential contributing factor is that your chain and/or chain ring appear to be quite worn. Look at how the chain is riding up the ramps of the teeth on the chain ring; enough that you can see daylight under it. That’s a sign one or the other is quite worn.

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Thanks so far for the feedback. Let me add some additional information:

  • The chain dropped once towards the frame and once away from the frame. All on the front.
  • I use a wheel-off trainer
  • Shifting works fine. Though hardly need it.

@onemanpeloton Meh, the TrainerRoad team called the workout type „sprint“. :joy:

:rofl: I’ll let you off

I know when I use my Kickr Core that I often have to adjust the rear mech slightly because the cassette doesnt sit perfectly in the same place as the one on my wheels. That’s worth considering maybe.

If the chain is dropping on the front chainring on both sides then consider adjusting both limit screws. Is this only happening under big power or was the other instance different circumstances?

Another possible thing to consider is chain wear. If you use a different cassette on the trainer and your wheel then the chain (unless youre changing this every time you get on the turbo) is going to be twice as worn as each cassette

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Dropped in the rear, right? And that was when you shifted?

@Triathlete I am a bit confused on your wording of a dropped chain

are you talking about the rear cassette chaining gears randomly - you will be pedaling along and all of a sudden it shifts into a higher or lower gear? sometimes as you continue to pedal it will suddenly shift back to the previous gear.

Or are you saying the chain fell off the front chain rings? (this is generally known as a dropped chain) The chain is no longer on the rings.

@MikeMckinney @rocourteau

Forgive me of I wasn’t clear enough. The chain dropped in the front. I did not shift. Trigger was the excess force during the sprints.

The multiple pics of the cassette with you pointing at the chain may have contributed to the confusion.

Ok, so dropped (not skipped?) at the front, no shifting, only under effort?

Worn chain + probably chainrings.

Second pix to last: yeah, as @geebutbut said, that chain is riding way high on the chainring.

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I would definitely check the chain and chain rings - there does seem to be some light in the front between the links and chain ring

are you getting in grinding noise or popping sounds when pedaling hard?

How old is the chain and front chain ring?

image

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Ah now I get the confusion. I wasn’t pointing but holding the cable away to allow for a better view of the cassette. :sweat_smile:

They are both about two years old. 600ish hours or so on the turbo. Perhaps 30 outdoors.

What was max power on the workout? Was it done in Erg?

It was 698 watts and it was done in erg mode.

^this

I would suggest a new chain ASAP - also get a chain checker tool - cheap and super simple to use

but you can also measure it as well https://www.parktool.com/blog/repair-help/when-to-replace-a-chain-on-a-bicycle#:~:text=Another%20ballpark%20method%20for%20checking,to%20the%20point%20of%20replacement.

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