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Thread: Chain break-in?

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    Chain break-in?

    Just changed a worn Dura Ace CN-7800 chain (5000+ miles, more than half indoors) for a SRAM PC-1050 on my road bike which is on a trainer for the winter. Nothing else changed. Noticed more resistance immediately, verified by higher heart rate (+3 to 4 bpm) at similar watts measured at rear wheel. None of the new chain's links were noticeably stiff nor was there any other sign of defect. Factory lube seemed normal.

    Is there a break-in period for new chains? Is the Dura Ace that much better than the Rival class SRAM chain?

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    Senior Member Retro Grouch's Avatar
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    I have no idea but that's an interesting observation. I think that it's neat that an ordinary guy can have instrumentation that precise. I'd be interested in if you get the same results tomorrow.

    Minus the instrumentation I was going to suggest you move your post to "Politics and Religion".

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    Quote Originally Posted by milmo View Post
    Just changed a worn Dura Ace CN-7800 chain (5000+ miles, more than half indoors) for a SRAM PC-1050 on my road bike which is on a trainer for the winter. Nothing else changed. Noticed more resistance immediately, verified by higher heart rate (+3 to 4 bpm) at similar watts measured at rear wheel. None of the new chain's links were noticeably stiff nor was there any other sign of defect. Factory lube seemed normal.

    Is there a break-in period for new chains? Is the Dura Ace that much better than the Rival class SRAM chain?
    I suspect the tighter tolerances of a new chain as well as the factory lube with a higher viscosity are the reason . I would imagine a couple hours of ride time will equal things out .

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    milmo, Welcome to the forum.

    3-4 BPM can be an allowable/expected difference between sessions, IMHO. True enough a new chain can become more flexable through use or may not initially mesh perfectly with 'used' gear teeth, creating a miniscule amount of added resistance.

    Not too long ago I replaced a XTR chain with a SRAM chain, without precise measuring eqpt. my seat of the pants impression was that there was no increased drag.

    Brad

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    Senior Member rydabent's Avatar
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    The heavy gunk lub that comes on new chains could account for some of the added resistance. But using some of the breakin knowledge from autos, bearing need to be broke in. On a microscopic level the surface of all the pins and rollers on a bike chain has probably millions of peaks and valleys. They rub against one another where the peaks poke thru the lube. On a car that is why you want to break in everything easy at low power settings. That way heat and pressure wont rip off the peaks down to a lower level. On a lesser level the same happens to your chain.

    Everyone has their own ideas about chains and lube. Personally I clean off all the factory lube on a new chain in kerosene, and relube it with Mobil 1. I have over 6000 miles on my chain, and my Park chain wear tool shows less than the .75% wear. However I ride a recumbent with its long chain. The heavy loads are when the rollers are on the chain ring and the freewheel. So there are more roller to take the sprocket wear. Mobil 1 almost eliminates wear in an engine, and seems to do the same on my chains.

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    Point taken on the heart rate variability between workouts. But I was at my standard mindless, movie watching, effort level which always kept me in a (Joe Friel/Gale Bernhardt/et al) Zone 2 HR range that now crossed over to a Zone 3 with the new chain.

    Rydabent's comments make instinctual sense. I just assume there's always a break-in period on mechanical devices, the question is whether it's noticeable in any particular case. And the factory lube does seem a bit viscous, doesn't it? Handling both chains when they were off the bike the old chain just flopped around easily while the new one did move more slowly.

    I'm tempted to experiment here by riding a few more times as-is to further verify the HR difference, then take the new chain off, strip the factory coating and relube to see if the HR/watts relationship returns to its previous state. When, and if, I do I'll post the results here.

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    Formerly Known as Newbie Juha's Avatar
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    Does the rest of the drivetrain have the same +5000 miles as the old chain? Cogs and sprockets wear with the chain, so a new chain on old drivetrain is not an optimal setup.
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    While there might be a bit of added resistance in the drivetrain based on the factors described in the prior posts, I think the band of variability is too narrow to account for the difference. Possibly it's biological not mechanical.

    Outdoor riding at decent speed provides efficient air cooling, vs. indoor training doesn't. Maybe you're seeing is the effect of added heat stress. There's also less efficiency in riding a bike that doesn't move under you as fluidly as one does in the real world.
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    Ride, Wrench, Swap, Race dddd's Avatar
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    I see three sources of chain friction on a drivetrain.

    Firstly, and minimally, there's the movements of the un-tensed portions of the chain, i.e. exiting the chainring, moving through the pulleys and engaging the cog.

    Secondly, there's the disengagement from the cog in back, where the tensed, bent chain straightens out while disengaging the rear sprocket.

    Thirdly, there's the engagement of the chainring, where the straight, tensed chain engages the teeth atop the chainring while bending to the arc of the chainring.

    Focusing on the second two processes involving the tensed chain, the friction there can be measured in terms of how far (vertically) that the chain deviates from a perfectly tangential entry/exit to/from the sprockets. This can be expressed as a fraction of the sprocket's radius, which translates into the same fraction of total power that is wasted.
    Note that this vertical measurement increases with cross-chaining and thus increases with any increase in link-to-link and link-to-tooth friction.

    The vertical distance as a fraction of the sprocket's radius represents the difference between the drive ratio (expressed by sprocket tooth count or "size") and the actual path of the chain in relation to the sprocket's center. This affects the chain's effective leverage (thus torque) acting on the sprocket. Thus any friction affects the drive torque, not the actual ratio of the entire drivetrain.

    I'm having trouble picturing any lube (or even lack of same) affecting the vertical height (path) of the chain by even one percent. The tensed chain does in reality deviate from a straight, tangent path between sprockets, due to friction, but the amount in reality is quite small, although admittedly a 1/2% deviation at each sprocket interface will equal a full 1% for the entire drive, and a very thick lube would further tax movement along the un-tensed length of chain along the bottom and thru the derailer pullies.
    Cyclists are sensitive to changes to their familiar steeds, and as a small difference of weight can be noticeable, perhaps less than 1% friction might also be?

    Regarding actual break-in, I always break in chains and/or sprockets by fully cross-chaining big-to-big and hitting some steep hills while of course making sure the front derailer isn't rubbing. This makes for a much quieter drivetrain, allowing brief cross-chaining with less noise and drag, while chain life is not measurably affected (and I've long used digital calipers to make comparisons).
    Especially during the initial break-in, significant added resistance can be felt during this severe cross-chaining, but you can actually sense that it goes away during the initial fraction of a mile of hard cross-chaining.

    Difficult to quantify, but perhaps it is better that this re-forming of the various mating part's "high spots" occurs initially while the lube is fresh and everything is clean? If this occurs after the lube is dirty, then wear (rather than burnishing and cold-forming) would represent more of the actual break-in process that eventually sets in.
    Last edited by dddd; 12-29-10 at 05:18 PM. Reason: clarity detail

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