Shimano Dura Ace chainring wear

Discuss light weight issues concerning road bikes & parts.
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pdlpsher1
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by pdlpsher1

I recently had a shifting problem and the root cause turned out to be the large chainring. While I was on the big ring (50 tooth, 9000 series), a downshift on the RD will cause the chain to drop from the big ring to the small ring. This was happening only on two gears....from 22 to 20 and 20 to 18. Initially I had thought this was due to the lack of BB bearing preload causing the crank to move laterally. I didn't find any play in the crank. Since I had a spare new Dura Ace chainring set on hand I decided to swap out the chainrings. After the swap the problem stopped completely. I analyzed the old and new rings and found the old ring had gotten much thinner at the tooth. There was no shark-tooth wear as I replace my chains at 0.50% stretch. It appears that the ring will eventually get thin due to wear and at some point it cannot hold the chain in place during a rear shift. I'm wondering if anyone has the same experience....having to replace the big ring due to thinness rather than tooth wear from the chain? Here are the pics of the new and old chainrings. I did measure the tooth wear on the old ring by placing a new chain on the ring and pull on the chain. There's a tiniest amount of movement on the chain, and this tells me that the tooth wear is very little. But apparently the wear (from shifting and cross-chaining) on the side of the tooth doomed the ring. You can see on the new ring there's a little high ridge on each tooth, and this ridge is absent on the worn ring. Apparently this high ridge is what holds the chain in place.

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Last edited by pdlpsher1 on Mon Jun 17, 2019 11:06 pm, edited 1 time in total.

dudemanppl
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by dudemanppl

If you replace rings, you should replace chain and cassette at the same time.

by Weenie


alcatraz
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Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

That's a very unusual problem.

Could your cables be crossed?

Looking at the big chainring chainline, what cog at the back would you say creates a straight chain?

How many km is that chain? Maybe you have a damaged/bent inner plate or quicklink or something.

What about riding without shifting on bumpy roads, has the front ever dropped a chain to the small ring?

Are there bent teeth on the old chainring? What about roundness? Some strong riders can bend chainrings. Also how tight were the chainring bolts when you took them off?

Do you usually use minimal preload when installing cranks? Try to move the crank along its spindle by pulling/pushing the arms and see if you can get it to budge. If you can it needs more preload.

Does it happen as frequently when riding with low power as high power/sprinting?

DamonRinard
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by DamonRinard

Hi pdlpsher1,

I think you've diagnosed the problem perfectly. Your thinking makes sense and the clear photos document the observed wear.

I've had similar experience with worn chain rings and bad chain retention. Nowadays with such delicately profiled teeth and the hard demands we make on shifting, plus the temptation to ride more in the big ring with compact cranks, I guess a chain ring can "wear out" in more than the traditional way now!

Just curious, does your tandem show similar wear?

Cheers,
Damon
Damon Rinard
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Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

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pdlpsher1
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by pdlpsher1

Thanks for the comments. The cassette is near new, with less than 2,000 mi. I had just changed the chain (a Dura Ace) prior to the chainring swap and the new chain/cassette didn't help. The problem is definitely the chainring since the issue stopped after the chainring swap. I just thought it's weird that a worn chainring on the side could cause the chain to drop to the inside. Hence my post here to see if others are seeing the same issue.

I have no shift cables since I'm running Di2. The dropped chain occurs when the chain has a perfect chainline. My theory is that when the chainline is not straight the worn chainring is able to hold on to the chain. When the chainline is perfect the chainring is too thin for the chain and can't hold on. The chainring is perfectly round and no damage other than the thin tooth. The chain drop only happened since two months ago, and I've gone through many chains and cassettes since the chainring was put into service. I have over 10,000 mi. on the rings but 1) I'm a spinner with a high cadence, 2) I'm not a powerful rider, and 3) I replace my chains at 0.50% stretch. The crank preload is set correctly and there's zero play when tugging the crank. The chain drop issue is occasional and I can't detect any patterns as far as power output or road condition.

Does anyone here ride with chainrings looking like mine or worse than mine? And have you experienced the dropped chain? From now on I will replace my rings before the high ridges are worn off. But damn I can't get these rings cheaply anymore from the U.K. :cry:

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Calnago
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by Calnago

Chainrings wear, just like cassettes. Not as fast mind you as the teeth are generally thicker and the rings are bigger than in the cassette. Just because you replace your chain when you’re supposed to does not preclude the rings from wearing in the same manner as if you don’t, but it will generally prolong things. How many chains have you gone through on that set of rings? Cassettes? My rule of thumb for all this really comes down to the quality of the shift. If you never swapped cassettes, rings or chains with other bikes then I think a pretty good rule of thumb is to replace the cassette after two chains have run their course over it, changing them as you are, at about the 0.50% wear mark. Chainrings last longer, and compact rings wear faster than larger standard rings. I just go by feel, as you have here. And especially when you put a new cassette and chain on, if the shifting is still bad, and everything’s adjusted properly, well... then it’s likely time for new chainrings too. Shimano chains, Shimano rings, Shimano cassette I assume. I also assume the front derailleur is zero’d in perfectly? It’s not the autotrim that’s partly to blame is it? Just thinking out loud here, but I suspect it’s just normal wear and tear. Unless chainring teeth are really bad, I find it almost impossible to tell if they’re ready for replacement without riding it.
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pdlpsher1
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by pdlpsher1

The weird thing is that I've had no shifting issues other than the dropped chain. And the dropped chain is caused by a rear shift, not a front shift. All Shimano parts (cassette, chain, and rings). This ring has gone through many chains....I've lost count. Perhaps 5-6. As for the cassette I have multiple wheels and all three of my cassettes look close to being new. I inspect the cassette with a 7x loupe and I can see the wear on the tooth. Amazingly there's very little wear on all of my cassettes, both visually and also checked with the Rohloff cassette wear checker. Yes the compact rings will wear out faster, and I think this is a perfect example here. The chain is steel and the ring is aluminum.....not a perfect combo as compared to the chain/cassette which both are steel. So the lesson learned here is to inspect the ring for wear more often. And the best way to check them is to place a new ring next to the worn ring. The wear on the old ring can be easily seen this way.

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tymon_tm
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by tymon_tm

this is weird. I'm a big ring guy myself (alhough I run 53) and I tend to get as low as 53/21 (on a 11-25 cassette) - mainly because my inner poseur tells me I'm more bad-ass conquering those small bumps on a large plate. you know, like a pro in a race :oops: (but then - if it feels faster, then even when it isn't, it's more fun that way 8) )

anyways, my last DA crankset lastet 3 full seasons, 2 of which it was my only bike (apart from winter strolling), so I figure they had like 30k km on them easily. I've gone through 3 cassettes, and hell knows how many chains (sometimes I would use 2 or 3 at once, sometimes I'd just use one till it's done) - all of them with quick links. I'm a spinner though, despite spending most of my rides in a big ring I'm stuck with Lance Armstrong as my *role model rider* and my chains always lasted longer than I thought they will*
(*there - I just came up with a perfect line for groupset ad :mrgreen: )

I've never occured such issues apart from poorly set up FD. I bought my bike with full Ultegra, but couldn't set up the FD without any rub - it was when I re-discovered bigringing, and expected my bike to provide me with all the gears possible. switching to DA solved the problem, it either had this ~1mm more travel I required or I was just lucky. but then I replace cables every season, and never had adjustment issues. switching through cassette while on big ring was always problem-less, and I bet the new owner will squeeze at least another 10k without a hassle (and for him it means like 3 years). I'd sometimes go as low as 53/23 for a brief moment, but then the chain was just too bent for my taste and the whole drivetrain produced noises suggesting I'd rather shift a gear or two up. but never, ever have I encountered something you describe. and I can't recall being forced to switch chainrings my entire life. yes I do know they wear, like anything else, but it never seemed to be an issue shift-wise. perhaps older groupsets had bigger tolerances, because I recall riding my DA 7800 for years and years (I basically skipped the 7900) and while the crankset looked appaling, it still performed... :shock: :noidea:
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alcatraz
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by alcatraz

I don't understand how the big ring can be worn either. You'd have to be a power rider, riding dry chains, for tens of thousands of kms, always in the big ring. How many small chainrings have you replaced? The wear on a small ring occurs quicker for the time spent using it as it's got 50% less teeth to transfer the load.

I had a friend that was dropping chains and it had nothing to do with the chainrings. His heels touched the chain when he was riding hard, and when in the rightmost cogs/chainrings made the chain drop. He also had a habit of sometimes backpedaling a bit which made things worse.

bikeboy1tr
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by bikeboy1tr

I replaced my big ring after just one season as I live in a relatively flat area and use the big ring frequently. My thought was the hollow big ring shows much wear in a short time. These rings are $200 a pop and thats when they are onsale so I decided to go aftermarket with rings that will last longer than one season. I never had issues with shifting from big ring wear but I decided to change it out when the offseason sales came.
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PeytonM
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by PeytonM

After 18k km I was having chain drops under load in the big ring (52 shimano). Bike had been well looked after with 3 cassettes and 5-6 chains at that point.

When changing the ring I noticed the wear was not even around the ring but in two locations that aligned with the power phase of the pedal stroke.

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pdlpsher1
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by pdlpsher1

PeytonM wrote:
Wed Jun 19, 2019 3:47 am
After 18k km I was having chain drops under load in the big ring (52 shimano). Bike had been well looked after with 3 cassettes and 5-6 chains at that point.

When changing the ring I noticed the wear was not even around the ring but in two locations that aligned with the power phase of the pedal stroke.
Thanks. I have similar mileage on my ring as well. Now I will keep an eye on ring wear and change the ring before it's too late.

by Weenie


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