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Home > Forum > Triathlon Forum > Chain jumps when sprinting

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Chain jumps when sprinting
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Dufflite
May 9, 20 6:40
Post #1 of 13 (3510 views)
Having issues with my chain jumping when power gets up to around 500+ watts or so.

Doesn't skip gears, just jumps, and at that power it's really jolting. Wouldn't want that happening on the road.

Put on a new cassette and chain, no change. Adjusted derailleur thoroughly. Cables also just replaced.

Starting to think it's the chainring now, but hoping for a second opinion before ordering a new one.

Ultegra 6800 crank, 52/36, has I think 5 seasons on it. It's on my road bike which I ride & race more than my tri bike.

Tried spinning up the small ring to over 500W - and no jump on the chain.

Filmed it and posted the video here:
https://drive.google.com/...K_Q/view?usp=sharing

Just noticed that after the second jump in the video when I stopped pedaling, the chain had fallen down to the small ring.

Thoughts? Anyone have experience with this? Time for a new chain ring?
Thanks
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Re: Chain jumps when sprinting [Dufflite] [ In reply to ]
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desert dude
May 9, 20 6:43
Post #2 of 13 (3506 views)
Had that same problem, changed everything. Got new rings problem solved. Had at least 15k on the front chainring. It had a noticeably different tooth profile when placed next to a new chainring
Brian Stover USAT LII
Accelerate3 Coaching
Insta

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Re: Chain jumps when sprinting [Dufflite] [ In reply to ]
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HTupolev
May 9, 20 6:56
Post #3 of 13 (3491 views)
Dufflite wrote:
Just noticed that after the second jump in the video when I stopped pedaling, the chain had fallen down to the small ring.
The chain falling off the big ring is what the "jumps" are. When the chain "jumps" in your video, the rear derailleur tension pulley is suddenly rotating rearward to wrap a bunch of chain. The chain isn't moving to a smaller cog in the back, so the only way slack this slack could have been introduced to the chain is if it's bailed from the big ring.
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Re: Chain jumps when sprinting [Dufflite] [ In reply to ]
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trail
May 9, 20 7:21
Post #4 of 13 (3470 views)
Another possibility other than a worn chainring is a bent derailleur hanger. Did your derailleur adjustment include derailleur hanger alignment?
Last edited by: trail: May 9, 20 7:21
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Re: Chain jumps when sprinting [HTupolev] [ In reply to ]
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Dufflite
May 9, 20 7:25
Post #5 of 13 (3462 views)
That’s what I’m thinking now, has to be slipping off the large chainring. This has been going on a few weeks but only this morning got around to making a video. Only way the jockey pulleys can kick like that is slack in the chain, and it’s not coming from the cassette so must be up front.

I did eyeball the hanger. Looks straight to me but I wouldn’t be able to tell if it’s off a mm or 2. And there is absolutely no lateral movement of the chain on the cassette cogs which is what I first suspected.
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Re: Chain jumps when sprinting [Dufflite] [ In reply to ]
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trail
May 9, 20 7:51
Post #6 of 13 (3442 views)
Dufflite wrote:
I did eyeball the hanger. Looks straight to me but I wouldn’t be able to tell if it’s off a mm or 2.

It is hard to eyeball. Just to rule it out you want to get your hands (or someone else's hands) on an alignment tool.
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Re: Chain jumps when sprinting [Dufflite] [ In reply to ]
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michael Hatch
May 9, 20 11:09
Post #7 of 13 (3352 views)
Put it the small ring and see if it jumps at high power.....
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Re: Chain jumps when sprinting [Dufflite] [ In reply to ]
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SummitAK
May 9, 20 13:15
Post #8 of 13 (3323 views)
Dufflite wrote:
That’s what I’m thinking now, has to be slipping off the large chainring. This has been going on a few weeks but only this morning got around to making a video. Only way the jockey pulleys can kick like that is slack in the chain, and it’s not coming from the cassette so must be up front.

I did eyeball the hanger. Looks straight to me but I wouldn’t be able to tell if it’s off a mm or 2. And there is absolutely no lateral movement of the chain on the cassette cogs which is what I first suspected.

Are you using a quick link for the chain? If yes, did you replace when swapping to the new chain?
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Re: Chain jumps when sprinting [trail] [ In reply to ]
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jaretj
May 9, 20 13:24
Post #9 of 13 (3317 views)
trail wrote:
Dufflite wrote:
I did eyeball the hanger. Looks straight to me but I wouldn’t be able to tell if it’s off a mm or 2.

It is hard to eyeball. Just to rule it out you want to get your hands (or someone else's hands) on an alignment tool.

The alignment tool is nice (I have one) but if you can't afford one you can take the rear derailleur off, then take the front wheel off, put one end of the skewer through the hanger and then the wheel on outboard side of the hanger. You can then use the front wheel compared to the rear wheel to see if the hanger needs aligning.

I got that from somebody here, can't remember who.
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Re: Chain jumps when sprinting [SummitAK] [ In reply to ]
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SBRinSD
May 9, 20 13:56
Post #10 of 13 (3305 views)
SummitAK wrote:
Dufflite wrote:
That’s what I’m thinking now, has to be slipping off the large chainring. This has been going on a few weeks but only this morning got around to making a video. Only way the jockey pulleys can kick like that is slack in the chain, and it’s not coming from the cassette so must be up front.

I did eyeball the hanger. Looks straight to me but I wouldn’t be able to tell if it’s off a mm or 2. And there is absolutely no lateral movement of the chain on the cassette cogs which is what I first suspected.

Are you using a quick link for the chain? If yes, did you replace when swapping to the new chain?

^^^ this - if you have a quick link that installed upside down it can cause a skip at high power. If you have wipperman link the jellybean shape should be facing down when it is on the bottom side of the chain ring.
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Re: Chain jumps when sprinting [michael Hatch] [ In reply to ]
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Dufflite
May 9, 20 14:59
Post #11 of 13 (3276 views)
I can get up over 500W without jumping on the small ring.

It's a Shimano ultegra chain and I used the new quick link that came with it, arrows pointing in the right direction. Honestly I much preferred when they used a pin.

I like the idea of checking the hanger by hanging the front wheel, I'll try that tonight.

Shopping for a new 52T ring now, good god it's expensive in Canada. $240 for my 6800 crank. I can get a whole new RC-800 for $360. Or, just go with a new 105 R7000 for a little less than the cost of a new ring. I do miss the days of cheap Shimano components from the UK.
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Re: Chain jumps when sprinting [Dufflite] [ In reply to ]
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MattyK
May 9, 20 22:19
Post #12 of 13 (3162 views)
I'll concur on a new big chainring.
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Re: Chain jumps when sprinting [Dufflite] [ In reply to ]
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Dufflite
May 26, 20 13:26
Post #13 of 13 (2944 views)
Updating for the benefit of anyone out there that might run into this same issue and are searching for solutions.

Installed new chainring, and problem solved, like magic!

H/T desert dude who called it almost instantly off the initial description.
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