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Old 08-20-12, 11:27 AM   #1
Medic795
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snapping chains like its my job

Hey again,

I have a 2012 Giant Talon 1. The stock chain is a KMC Z7. 2 months ago I was riding a trail, hit a step part while I was in to high of a gear (meaning a smaller gear in back and large in front). I stopped at the bottom, shifted while I spun the back wheel in the air to shift to a lower gear, hopped back on, pedaled up, and promptly snapped a link. Got some KMC masterlink II, put on it, and let the bike sit for a while (couldn't get a chance to get out and ride). I rode 1 time on a paved path with road tires on, no problems. Then the bike sat for a bit again.

Fast forward to yesterday. Went riding on trails, went up a steep-ish hill in a low gear (smallest cog up front and second to largest in back), wasn't standing up on the bike at all, and was pedaling with a good cadence (around 90). Halfway up, snapped another chain. I didn't have a second master link, and I wasn't able to get the chain back together, so I had to walk the bike back to my car. Thank goodness I wasn't too far from the end of the trail.

I did some research on the KMC site, and the Z7 chain is "7 speed (casual 8 speed)" chain. The measurements are 1/2" x 3/32". Now, I'm 6'3" and 307 lbs. I have always had super strong legs. Is there a super strong chain I can buy that will fit?? I was looking at the KMC X8.99 chain. The measurements are the same. Will this chain work? Its meant for an 8 speed bike (which I have, 8 in the rear and 3 up front). It also says that its got mushroom pin rivets, and it is super stretch proof. Think this will be strong enough? I love riding, its really helping me get back into shape, but obviously it kills the fun if I can only bike for a bit before I break it.
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Old 08-20-12, 11:52 AM   #2
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Interesting question. I'm 380 pound and my son is just over 300. In the last 8 months of riding (10-30 miles a week, not a lot), I have broken only 1 chain and my son hasn't broken any. My chain only broke because I got lazy while at the bike coop and needed to extend my chain which was one link too short and just grabbed a piece of chain laying on the ground and extended it with that piece. I snapped it at that exact link when I was mashing up a steep hill.

I'm not really sure what to tell you other than I use a mix of Shimano HG chains, KMC cheap 6-7-8 speed chains, and even the cheap 12-24 speed chains you can get at walmart for under 8 dollars. My bikes are either 7 or 8 speed. I don't use master links. I find using chain tools to be easier.
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Old 08-20-12, 12:35 PM   #3
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It sounds like when you down shifted off the bike it didn't shift correctly, binding the chain somehow and it snapped. This probably weakened other links so during your next off road ride you snapped another previously weakened link. Your not going to find a chain significantly stronger than the one you are using. With someone of your weight and strength you can easily snap chains, especially off road. You will need ease off when shifting, shift to the next gear and after you feel it engage continue riding hard. This goes double for shifiting the front chain rings; in this case you should always shift up or down before you need the gear change, ie shift the front just before the hill, not when you've already started climbing and realize you are in the wrong gear; you will need to look ahead and anticipate the need for shift. I taught Police bicycle patrol for years and it was the big inexperienced riders that tended to snap chains; once they eased off a little tha problem would disappear.
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Old 08-20-12, 01:30 PM   #4
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Sure an 8 speed chain will work on an 8 speed cassette. At your weight, I'd concentrate on staying in a low gear that premits a relatively fast cadence and make sure to shift early, so you're not shifting with a high chain tension - that alone can break a chain due to excesive side forces, prying a plate off the pins. Chains rarely break due to high tension only.
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Old 08-20-12, 02:05 PM   #5
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I do have a problem with shifting under pressure. I try to stay in the higher gear to keep the momentum up, then by the time I realize I need to shift lower its too late :-\. I am pretty inexperianced.

So with the potential for already weakening the chain, I should probably just start from the beginning and grab a new chain right?

Do you guys think the X8.99 is a good chain?
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Old 08-20-12, 02:11 PM   #6
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+1)
Sounds like a technique problem .. read the terrain anticipate the shift points ,
let up on the pedal force , and let the mecanisims features work as designed.
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Old 08-20-12, 02:28 PM   #7
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Usually chains break in a two step process, and not directly from tension.

The process starts with hard shifting, which forces the plates apart pushing one to (and beyond) the end of a pin. You cna hear this happening as you shift. A smooth shift sounds like the clickery-click of a train passing over a switch. An pooor shift under load makes a particular kRRRUNCH sound as the chain is twisted and forced onto the teeth of the new sprocket before disengaging from the old one. There'll often be a bit of a pop immediately as it's torn free at the top.

The poor shifting pushes the plates to the point that they're ready to come off the pins, but they'll stay there for a long time functioning normally until a time pf peak tension, like climbing an embankment when one plate falls free, and it's companion bends letting the pin slip free.

I had a friend who also broke chains as you do, so I cut a square notch out of an old credit card which just cleared the width of the chain. We'd run his chain through and the wider links would snag, thereby showing themselves. Sometimes we'd find 5-10 links spread this way including a few which were obviously barely on the on the pins.

The soulution isn't a better chain, but to eliminate those hard, under power shifts which are the real cause of your problem.
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Old 08-20-12, 02:28 PM   #8
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Are you using the master link to close the loop or are you pushing the same pin back in?
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Old 08-20-12, 02:44 PM   #9
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As far as shifting under load, there are 2 big hills near me on my ride. Well big to me. When I approach them, I am usually in the middle ring in the front (40) and am in the middle of the rear of an 8 speed mountain style cassette.

As I go up the hills, when I have to shift, I will allow my feet to slow down to the point of just not actually providing any power to the bike and then I shift while "coasting" though that one pedal revolution. Then I pedal faster to make up the lost momentum and continue. Sometimes I have to do that 3 times on one of the steeper hills.
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Old 08-20-12, 02:56 PM   #10
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Quote:
Originally Posted by Medic795 View Post
.....I was looking at the KMC X8.99 chain. The measurements are the same. Will this chain work? Its meant for an 8 speed bike (which I have, 8 in the rear and 3 up front). It also says that its got mushroom pin rivets, and it is super stretch proof. Think this will be strong enough?......
I've used and recommended the KMC X8.99 chains, and yes it will be more durable than the Z7, but I would agree with many of the other post that suggest improving you shifting techniques as well. At 300lbs you are definitely stretching the design limitations of most cycling components, so you are going to need to compensate by developing more finesse. You shouldn't really have too much of a problem with this if you just remember that the more practice you get at being smooth and relaxed in the saddle, the better you will be able to over come obstacles on the trail and the less stress you will put on your bike. Ride Safe!



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Are you using the master link to close the loop or are you pushing the same pin back in?
I believe he is using a KMC M/L-II master link that avoids pins and doesn't require tools:

Last edited by Stealthammer; 08-20-12 at 03:04 PM.
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Old 08-20-12, 04:46 PM   #11
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"The soulution isn't a better chain, but to eliminate those hard, under power shifts which are the real cause of your problem."

A agree with others that at 300+, most of the bike's drivetrain is highly stressed, but the different price-points of chains offer increasing levels of strength, as has been published.

I would use a Shimano chain, HG-70 or better.

I have broken SRAM chains, even expensive ones, and have seen several of the Bell (TaYa/Wallmart) chains break as well.

My thought is that, obviously, Shimano has a reputation for extensively testing their drivetrain components, so why use anything else?
I also find that Shimano chains seem to be much more tolerant of scant lubrication than others, an indication of superior metallurgy.

I've sold bikes to riders over 250#, and am cautious about chain quality and that a freehub-type of double-wall rear wheel is always used.
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Old 08-20-12, 05:24 PM   #12
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"The soulution isn't a better chain, but to eliminate those hard, under power shifts which are the real cause of your problem."

A agree with others that at 300+, most of the bike's drivetrain is highly stressed, but the different price-points of chains offer increasing levels of strength, as has been published..
The tensile strength of all 3/32" bicycle chains falls into a very narrow band, with none materially stronger.

What is different is the type and degree of peening to prevent plate spread. So better chains will be more resistant to the effects of poor shifting technique. But since no chain is proof to it, the best solution remains in solving the poor shifting problem, not trying to defend against it.
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Old 08-20-12, 05:30 PM   #13
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Strength wise the KMC Z7 is about a s good as it gets for a chain. I have riden these for years busted and put back togehter just fine I just have never seen one fail.
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Old 08-21-12, 04:16 AM   #14
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Originally Posted by Medic795 View Post
So with the potential for already weakening the chain, I should probably just start from the beginning and grab a new chain right?
I'd consider the entire chain retired after the first break. What ever force or shifting issue that caused the first break has affected the whole chain, not just the point of failure.
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Old 08-22-12, 12:34 AM   #15
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"The tensile strength of all 3/32" bicycle chains falls into a very narrow band, with none materially stronger. "

Any data published to support this?

I've seen SRAM and TaYa/Bell chains fail in tension with broken links after very short usage periods. Shimano and KMC chains don't seem to do this.

The published "strength" of various chains within a specific manufacturer's lineup are sometimes specified as "pin power" or some-such, but I've never seen any published data to suggest that the tensile strength does not vary by model or manufacturer. I can't think of any reason that a much more-expensive chain with higher specified pin or riveting strength would not also feature higher material specification throughout, and I would bet that they do, at least coming up from the lowest price-points.
But again, in my experience, it has been differences in the brand of chain that seems to show the most dramatic differences in tensile strength.

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Old 08-22-12, 02:00 AM   #16
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From KMC:

The Z7 is an entry level 8 speed chain meant for Shimano HG systems. Next is Z8, then X8.93, then X8.99.

The X8.99 is our highest end 8 speed chain - also meant for HG systems. Pin power and tensile strength are significantly increased on this chain thanks to riveting tech and pin conditioning.

Let me know if you have any questions.
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Old 08-22-12, 02:03 AM   #17
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About KMC missing links (connecting links):
Please note that there are 2 different sizes of 8 speed chain; 7.1mm and 7.3mm. The latter is used for HG systems and needs to use this connecting link http://www.kmcchain.us/kmcproduct.as...id=34&ssid=572

For HG systems, make sure the connecting link says CL573R (as opposed to CL571R for other systems).
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Old 08-22-12, 06:35 AM   #18
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I haven't stayed on top of this for years, but to my knowledge all bicycle chains have tensile strength ratings of 1100-1200kg. I remember that there's a standard for them at 1,000 or 1100kg but don't remember if it's an old US or European industrial standard, or a national standard. In all likelihood it's now an ISO standard and is somewhere in that range.

But comaring tensile load ratings is pointless because tensile chain failure (plates failing under load) is extremely rare. When it happens, it's usually the result of heat treat and/or tolerance issues causing outer plates to stress crack at the pins. Another cause is embrittlement caused by exposure to various ions, mainly hydrogen and chlorine, in cleaning solutions, but this too is rare.

99% of chain failures happen in the two step process I described earlier. Shifting forces plates outward to and beyond the end of the pin, and at a later time a peak tension load snaps the chain. The evidence is clear, 1 plate intact but detached at one end, and the other bent when the pin slides free.

Traditionally chains have been made of carbon steel plates, with bearing grade pins and bushings, but the current bushingless design and thinner plates today narrows the options. Alloy steel is used for the plates, but heatreating for maximum tensile strength is limited by the need to maintain ductility and toughness. The inner plate also has to be heat treated to a balance the wear properties against toughness (opposite ends of the scale) which is one reason wear life is down compared to 30 years ago (smaller contact area being the main other reason).
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Old 08-22-12, 02:23 PM   #19
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"...which is one reason wear life is down compared to 30 years ago..."

I wonder if that popularly-held assertion is correct.

I have over the years obtained and ridden quite a few as-new, older bicycles with their traditional bushing chains, and to the extent that I actually measured chain elongation over time, I would say that most of the older chains showed more-rapid elongation as compared to contemporary Shimano chains, while also requiring much heavier lubrication.

There is also the matter of how many miles that most bikes were actually ridden during the earlier years (remember no, or perhaps one 19oz water bottle being so common), and also the common practice in those days to let the chain elongate to perhaps several % before any chain or sprocket replacement was considered (I doubt that today's shorter, shaped sprocket teeth would tolerate that).

I have to say that I am quite pleased, and amazed at times, how slowly that contemporary Shimano chains suffer elongation while in heavy service.
Contrasting that to the very rapid elongation of those first-gen, bushed UniGlide and Lanner chains.

Among current chains, due to observed differences in wear rate (and the degree of lubrication required to keep the chain from squeeking), I would guess that there is a large variability in the metallurgy of various chain's parts.

With the introduction of 10s road drivetrains, there is the too-frequent referral to "worn-out" chains which merely no longer will provide the lateral stiffness to maintain the conveyance of derailer movement into an actual shift. In such cases, typically with the widest-ranging road cassettes, I usually advise that only the use of a non-floating upper (guide) pulley will assure a decent service interval in keeping with the expected (~3-5 thousand miles) service life of a high-quality chain. It's either that, or going nuts with chain replacements and cable service.

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Old 08-22-12, 02:36 PM   #20
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"...which is one reason wear life is down compared to 30 years ago..."

I wonder if that popularly-held assertion is correct..
Wonder whatever you want. I don't have a dog in this fight.

I post here to try to help people with technical problems, like the OP, who I firmly believe is most likely to solve his chain breaking problem by focusing on his shift habits, rather than hoping a stronger chain will make the difference. My opinion is based on 40+ years in the bike industry, and a good knowledge of the subject. Of course he's free to consider my advice in the light of any other advice he's getting.

But I don't have the time, patience or interest to debate the fine points of chain design and construction just for the sake of doing so. You're free to believe what you want and make your decisions accordingly, as is the OP and any other person on this forum.
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Old 08-22-12, 02:54 PM   #21
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" You're free to believe what you want and make your decisions accordingly, as is the OP and any other person on this forum..."

I do, and I will. We all have our opinions, and mine is that a stronger chain is a very good idea for this OP.
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Old 08-23-12, 09:18 AM   #22
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As far as shifting under load, there are 2 big hills near me on my ride. Well big to me. When I approach them, I am usually in the middle ring in the front (40) and am in the middle of the rear of an 8 speed mountain style cassette.

As I go up the hills, when I have to shift, I will allow my feet to slow down to the point of just not actually providing any power to the bike and then I shift while "coasting" though that one pedal revolution. Then I pedal faster to make up the lost momentum and continue. Sometimes I have to do that 3 times on one of the steeper hills.
It does sound like your waiting a bit too long to shift, although your approach is correct. One pedal revolution may not be sufficient to get a clean RD shift. You might also check your RD to make certain the pulleys haven't developed some slop - this would cause hesitation in the shift.
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Old 08-23-12, 03:49 PM   #23
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It does sound like your waiting a bit too long to shift, although your approach is correct. One pedal revolution may not be sufficient to get a clean RD shift. You might also check your RD to make certain the pulleys haven't developed some slop - this would cause hesitation in the shift.
+1 here.

Anything that keeps the chain moving a little faster should improve the chain pickup rate toward a cleanly-completed shift.

Same goes for riding in a bigger chainring, the chain moves faster and with lower tension force for a given "Pedal speed".
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Old 08-23-12, 08:31 PM   #24
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Also practice on letting up on leg-pressure without reducing speed while you're shifting.

I assume the "break" in the chain is the pins pulling out of the plates due to lateral torque. You're not actually snapping a sideplate in 1/2 are you?
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Old 08-26-12, 08:24 PM   #25
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They aren't snapping in half. What appears to be happening is that the side plate is bending away from the pin and its breaking the chain there. Based on what people are saying, and my ****ty shifting technique, It seems like if I work on the technique the problem will go away. I got a new KMC X8.99, so I will throw that on and see how it goes I always thought bike parts were more expensive. I might replace the chain and cassette once a year for 50 bucks or whatever. Seems like cheap maintenance to me
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