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Thread: Chain Popping Off Big Ring Under Full Power

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    Default Chain Popping Off Big Ring Under Full Power

    I have been asked to help a riding mate who is truly stumped by a chain popping off under full power riding shenanigans. He has a quite new Cannondale System Six with Ultegra Di2, SiSL crank with powermeter and Absolute Black round chainrings. Everything is adjusted well but when he does a full power sprint, the chain pops off the outside of the large chain ring and almost makes him crash. The front derailleur has been lowered to the point of compromised shifting and the limits were temporarily adjusted to the point where it was slightly rubbing and it still kicked the chain off under power.

    Chain rings are straight, BB is free of play and has been replaced with an Enduro thread together PF30 unit just to make sure. He also replaced the big ring for safe keeping but it still pops off under ~1400 watts. (I don't have to worry about such issues)

    What else could this be? That Cannondale crank, nor the rings are flexy, BB is not moving inside the shell. No creaks or movement that can be seen or felt when you pedal or tug on anything. His shop can't replicate it and he doesn't want to keep replacing parts unnecessarily. It is one of those highly integrated aero bikes. Could the frame be flexing enough under his ~200# weight and power to pop the chain off? What would you try next?

    Thanks again.
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Bent tooth or bad link?
    Bill Fernance
    Bicycle Shop Owner
    Part Time Framebuilder
    Bicycle Tragic

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Depending on where in the pedal stroke it's being forced off, could be loose BB too.

    My bet is on bent rings tho.

    M
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Could the rings be bending or flexing while riding? The first Absolute Black ring popped the chain off and the brand new one does the same.

    We should dig up a different big ring and give it a try.
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    there is a reason quickstep dropped FSA after they were dropping chains in the sprint

    stuff like absolute black rings are built for weight weenies and climbers. Get a 9150 crank on there and they will never drop a chain again

    i've seen it first had a few times with specialized crank/rings (fsa rings?) and some old sram red rings. The new hollow d/a rings are super stiff and you won't have an issue

    edit- because the friend has a powermeter i'd try one of the cannondale 1 piece chainring setups and see if that helps. Big dude pushing big watts throwing the chain is almost always equipment failure
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Have a buddy who at one point was 220 of solid muscle (body builder) who rode as his “cardio”. The was in the mid 1990s and he had one of the overly stiff Cannondale AL frames. He complained of ghost shifting all the time. No one could fix it or replicate it. One day, a good mechanic was riding behind him and could watch the bike flex under his weight and power when he laid into it.

    If your friend is +200 pounds using that crank ring set up, I agree with Andrew. Have him try a pure 9150 or even Ultegra set up.
    Applying what works for a 140-170 pound rider that can produce high watts is not the same as someone +200 applying those watts. Especially in a sprint.

    BTW - the buddy I mentioned above is now ~175 pounds and snap out 1600 watts. He rides complete dura ace groups and doesn't have any issues.
    Brian McLaughlin

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Having been that guy 200lbs+ and strong watt sprinter. I could bend some rings at will. If frame flexed chain fell off. If the frame was stiff chainrings bent, collapsed and failed. Went to crankset using Shimano two-piece chainrings no more. Only on a few very flexy frames could I drop the chain. If he is using an oval Absolute Black ring. It will probably continue. To the suggestions above any Ultegra/Dura Ace crank and chinaring set up can be abused yet still work very well. I have no real world experience on the new SRAM AXS, or the one piece Cannondale rings.
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    A steel keirin bike under a keirin racer (François Pervis) in a very low (46-14) training gear for velocity. Imagine that under a kilo TT effort with his regular gearing.



    A cannondale systemsix is not traditionnal a steel keirin bike, but it is made for 70kg pro road racers so it has probably a lot of flex. I'd recommend using non third party weight weenies part at the transmission front.
    Last edited by sk_tle; 1 Week Ago at 07:01 AM.
    --
    T h o m a s

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Thank you very much for the help. I am surprised to hear that Absolute Black chainrings are considered weight weenie fodder. I assumed they were pretty heavy. That being said, I will share the information with him and see what is more important, sunk costs or a solution.

    Thanks again!!!
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Great vid, never seen one like that before, thanks for posting.
    Stay strong in this time of crisis and realize sadness and grief are part of the process Brian Clare

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Quote Originally Posted by houston View Post
    Thank you very much for the help. I am surprised to hear that Absolute Black chainrings are considered weight weenie fodder. I assumed they were pretty heavy. That being said, I will share the information with him and see what is more important, sunk costs or a solution.

    Thanks again!!!
    it's an unfortunate situation. Maybe the friend can get a conversion BB to try a different crank and see if that helps before dropping the money on a new one

    riders who shift into a very heavy gear, then wind the sprint from ~60rpm will see more issues.
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    I presented the findings and was met with skepticism. I think the sunk costs are so high that changing behavior will trump changing the equipment. The rings that came with his bike are FSA something so going back to those will probably make the situation worse.

    Nobody ever regretted buying a Shimano crank.
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Understandable.

    Correct- no one regrets buying Shimano, or Campy, crankset with their rings. And using their BBs.
    And chains
    And cassettes
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    I am not familiar with the crankset in question. Can it take chain rings from Praxis Works? If their claims related to their forged -- instead of machined -- chain rings are more than just marketing guff, could it be a less expensive solution?
    Chikashi Miyamoto

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Quote Originally Posted by Chik View Post
    I am not familiar with the crankset in question. Can it take chain rings from Praxis Works? If their claims related to their forged -- instead of machined -- chain rings are more than just marketing guff, could it be a less expensive solution?
    That's a great question. I think it is a standard bolt 110mm bolt pattern so it could be a less expensive trial than new BB, crank, powermeter, etc...
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    I've had really good luck with the praxis rings over the years. They're not as refined as rings from any of the big 3, but they do work well. I weigh quite a bit less than 200lbs and can't put out quite as many watts as you mention your buddy can (but at my max I'm not too, too far off) and I've never dropped a chain with them.

    A bunch of knowledgable people posted up thread, so there probably is something to the absolute black rings being the culprit, but just to rule out another issue, does that SiSL crank have any type of bearing pre-load setup? The only time I've ever had issues with chain drops was when a mechanic once failed to tighten the SRAM Red BB30 preload enough and under hard efforts the crank would shift a mm or two to the non-drive side and pop the chain right off. Once I figured it out I tightened the preload an eighth of a turn and bam, everything was solid from then on out.
    "I guess you're some weird relic of an obsolete age." - davids

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Quote Originally Posted by Matthew Strongin View Post
    I've had really good luck with the praxis rings over the years. They're not as refined as rings from any of the big 3, but they do work well. I weigh quite a bit less than 200lbs and can't put out quite as many watts as you mention your buddy can (but at my max I'm not too, too far off) and I've never dropped a chain with them.

    A bunch of knowledgable people posted up thread, so there probably is something to the absolute black rings being the culprit, but just to rule out another issue, does that SiSL crank have any type of bearing pre-load setup? The only time I've ever had issues with chain drops was when a mechanic once failed to tighten the SRAM Red BB30 preload enough and under hard efforts the crank would shift a mm or two to the non-drive side and pop the chain right off. Once I figured it out I tightened the preload an eighth of a turn and bam, everything was solid from then on out.
    people throwing chains due to wattage is rare during a smooth, steady ramp to peak wattage. Often it is riders who hit a sprint overgeared, and muscle the gear up from 60rpm. Doing this usually involves canting the bike a fair bit which will exacerbate any flex issue
     

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    Default Re: Chain Popping Off Big Ring Under Full Power

    Quote Originally Posted by Bewheels View Post
    Have a buddy who at one point was 220 of solid muscle (body builder) who rode as his “cardio”. The was in the mid 1990s and he had one of the overly stiff Cannondale AL frames. He complained of ghost shifting all the time. No one could fix it or replicate it. One day, a good mechanic was riding behind him and could watch the bike flex under his weight and power when he laid into it.

    If your friend is +200 pounds using that crank ring set up, I agree with Andrew. Have him try a pure 9150 or even Ultegra set up.
    Applying what works for a 140-170 pound rider that can produce high watts is not the same as someone +200 applying those watts. Especially in a sprint.

    BTW - the buddy I mentioned above is now ~175 pounds and snap out 1600 watts. He rides complete dura ace groups and doesn't have any issues.
    I was watching a former NFL pro race his bike in Manassas, VA one day. Man! Was that Ti bike flexing and screaming!

    I *think* it may have been Skip Foley.

    M
     

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