Bicycle Mechanics - Increasing Chain Life by reversing its run ?

I read the other day that reversing chain direction when allowed, every so often will increase the life of the chain. As I understand chain wear is due to the pins wearing within the rollers, I fail to see how reversing chain direction would affect chain life. Thoughts?

I doubt it would make any difference. Some chains, such as the newer DuraAce chains are directional. Get a chain gage to periodically check your chain.

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I think I read something along that line a few years ago. Shimano engineers were able to double chain life by reversing the direction after a very "specific quantity" of wear.

I don't, for the life of me, remember where I read it.

If I'm seeing this right when the crank is turned it loads one side of the chain pin and when it transmitts the power to the rear cog the pin is loaded the other way. But the load on chain around the crank ring is spread over say half of 52 teeth were the rear load is spread over half of maybe 12 teeth so I would expect one side of the pin to wear 4 times more load per pin, wears 4X faster? (52/12)=4+ Reversing the chain would even out the wear??? The chain also has to pivot more around the rear cog too. Wonder if they mean breaking the chain and reversing inside to outside this way the chain would pivot the other way?
Just a theory

I read something along that line a few years ago. Shimano engineers were able to double chain life by reversing the direction after a very "specific quantity" of wear.

Thats exactly what I had read, that Shimano engineers were albe to double chain life. I found this in a book called ( Bike Touring ) by the Sierra Club.

Logically there has to be some benefit to this. The pins in a chain are riveted in, so putting the load on the other side should result is some gain in overall wear.

In the past you could double the life of a freewheel by reversing the cogs since the cogs were symetrical and had no shaped or ramped teeth to aid shifting. All of the wear was on the trailing edge of each tooth so reversing the cog exposed the unworn side. That's no longer true with current cassettes and even recent freewheels since the cogs are "keyed" to the ratcheting body and only go on one way.

Chains do wear unevenly, and reversing the direction will increase the life slightly, but nowhere near double. Also since the chain only flexes under load in one direction only, from straight to the inside of the loop, the pin wear will be asymmetrical with more wear toward the inside (bottom while on the upper loop). So there will me some benefit in flipping the chain, so what was on the outside of the loop is now on the inside. Again it won't be anywhere near double.

The only proven way to improve total drivetrain performance is by starting with 2-5 chains with a new cassette and chainrings, and rotating them every 500-1,000 miles. This ensures that the chains and sprockets stay closely matched for wear patterns, and will both increase sprocket life and running smoothness compared with replacing chains as they reach the 1/2% wear mark.

It also affords plenty of time to thoroughly wash and properly lube the chains while they're on deck. The benefits have to be weighed by the cost of pins or non-reusable links, but definitely makes sense if using reusable connectors (keep the connectors with their chains for life). Since you're rotating the chains anyway, might as well flip or reverse them if their design allows.

Well...I'm certainly no engineer, and opinions of those I respect here have already been stated, so I'm somewhat reluctant to reply here.

It doesn't seem to me that reversing the chain would amount to any benefit. Whether the wear occurs on (or mostly on) one side of the pin or the wear is evenly distributed between two load-bearing sides, the total wear still amounts to "1." That is, whether it's 50/50 or 90/10, it's still basically the same wear that contributes to the total wear and should be reflected in the same amount of chain stretch. Is it not??

I did the reversal routine through the lives of a couple of chains and didn't notice any difference in the life of the chains and haven't bothered with it since. Yet, I realize a "lab test" with real controls could show something otherwise.

What FB writes makes a great deal of sense. Thing is, reversing chain direction won't do much to change the wear on the pins. Turning it inside out will make a bigger difference, though still a marginal one, I think.

As I understand chain wear is due to the pins wearing within the rollers,

you left out the bushing in this , there was a tube joining the inner side plates,

It's still there for some 1/8" chains, 'full bushing'
derailleur chains replaced the bushing with a lip of
Metal raised, when hole is punched out of the inner link side plate.

that is bushingless chain, all derailleur chains use that Mfg technique now,
because it's more laterally flexible.

the wear is mostly that lip wearing thin , from both the roller edges, and the pin passing thru on the inner surface.
http://en.wikipedia.org/wiki/Roller_chain

I agree. Inside out makes more sense, but it wont double the life I'd think.

What happens in a controlled environment is not like the real world(new car gas mileage ratings for example)

None of it makes sense,you can't put a load on one side of a chain if the ends are hooked together.

On a non-directional chain (aka a "symmetric" chain), it doesn't matter directionally which way the chain is applied, and so it should not hurt to remove the chain and reverse the direction. And for most chains today that don't have a special master link, you still require a chain rivet tool to push the pin mostly out to remove the chain for a thorough dunking in cleaning solvent. I've been using this as an opportunity to reverse the chain for decades now, and it naturally makes sense. Why? Because I'm lazy and need to flip the chain around so the pin that got pushed out and was facing into the bike, is now facing outside toward me so I don't need to try and push the pin back in from the other side of the bike. I stand or sit on the same drive side of the bike and reconnect the chain by pushing the pin back in from the same side I pushed the pin out originally.

And the upshot? Well, I do replace chains, but for a big guy my size, I really don't get the same level of wear some other folks seem to be reporting. I get much higher mileage on my chains. Maybe 7K - 10K on most of my bikes that have maybe had chains swapped out once in 20 years. And it makes me wonder if the wear and stretch comes more from slow abrasion from dirty chains than actual tension on the chain. Because certainly I exert a lot of tension, but I don't see the level of stretch others seem to report. However, I do clean my chain fully with solvent almost every month. Maybe I've got far less dirt and grit on my chain, and that's probably why it's lasting so long. I used to be afraid that my rough handling of chain link pins would wear out the center holes and the more I'd push pins out and back in with the chain tool, the greater the chance I might repeat with the same link too often, then I'd have that link someday fail. But that has never happened even once in decades of cleaning my chains. So side plate wear at the link pin holes must not be significant, even with habitual removal of pins. Maybe the secret to avoiding chain stretch is actually keeping it clean.

Think I'll give it a try, out of curiosity.

Northwestrider, Because the chain often works under vary'g lateral and inline torque stresses with a derailleur design I don't see where a measureable benefit in chain life would be noticed. Chains operating in a fixed chainline (fixie, SS or IG hub) may see a longevity benefit from reversing torque loading.

Just thinking out load... I really don't know.

Brad

Northwestrider, Because the chain often works under vary'g lateral and inline torque stresses with a derailleur design I don't see where a measureable benefit in chain life would be noticed. Chains operating in a fixed chainline (fixie, SS or IG hub) may see a longevity benefit from reversing torque loading.

Just thinking out load... I really don't know.

Brad

Your logic is sound... which is why I think it's the cleaning of the chain that prolongs the chain. The side plates are metal. They aren't really stretching. Where the ends of the link pins press into the side plates, the locations are fixed, so there is no movement and therefore not much chance of abrasion. And the pins are hardened steel and short things, so we just aren't that strong to do that much deformation. But the center section of those link pins do undergo pull and some pivot by the inner links as the chain goes around the drive train. And IMO, this must be wearing out faster when dirty. And that must be the mode of stretch - the wear on the center axial surface of the link pins.

Now, of course, the rollers that are sandwiched inside the inner links and contact the gear teeth directly must also wear. But they are centered on the link pins, and can't directly affect the chain length. Maybe they get smaller, just like tires losing a thin layer of tread as they wear, but the wheelbase remains the same. However, because each inner link pulls on the outer links by alternating between force on the outer edges of the link pin press fit into the outer link, and the center of the inner link that pulls on the center of the link pin, if the center of the pin gets worn and is narrower, the chain will stretch.

Me too thinking out loud.

Seems to me that it wouldn't really make much difference - the chain is still going to be in tension so you aren't really changing any of the forces on it, just it's direction of travel.

How many speeds? Lower speed chains (7 and under are cheap). I would not want to be cheap about chain, and then wear out a more expensive cassette. I pay under $5 for 5/6 speed chain, and under $6 for 7 speed chain.

Think I'll give it a try, out of curiosity.

If you remove the chain to clean it you already give it a try since 50% of the time you will reinstall it in reverse.

Chain elongation occurs due to the wear on the pins and the bushings formed into the inner side plates, not the rollers. I've done a fair amount of chain wear testing and found that the roller wear is huge, compared to the pin/bushing wear. When a chain has elongated by .5%, each pin and bushing have a combined wear of only .0025 inch. Campy chains elongate far less than any other brand. I've measured the elongation on a Campy 10 chain to be as little as .15% after 6,000 miles of use - much of it climbing gritty roads in the Colorado mountains. The roller wear on a chain with that much use will be much greater. The OD of a roller may be .005 inch smaller and the ID about .010 inch larger. The space between the rollers may increase from .200 inch to .240 inch. The side clearance, will also have increased to around .013 inch, or about twice the original amount. The bottom line is that the chain was totally shot, even though the elongation was small. In this case, measuring elongation properly - with a full length measuring tool gave the idea that the chain was in good shape, when it was not. Most other brands would have elongated into the .75-1% range with that much use.

Flipping a chain is thought to increase chain life because the wear is not centered over a 180 degree arc with endpoints that are perpendicular to a line through the pin centers. When a chain is flipped, a little of the unworn pin area is being used. Flipping a chain does not change the wear area by 180 degrees, from the back of the pin to the front.

Chain elongation occurs due to the wear on the pins and the bushings formed into the inner side plates, not the rollers. I've done a fair amount of chain wear testing and found that the roller wear is huge, compared to the pin/bushing wear. When a chain has elongated by .5%, each pin and bushing have a combined wear of only .0025 inch. Campy chains elongate far less than any other brand. I've measured the elongation on a Campy 10 chain to be as little as .15% after 6,000 miles of use - much of it climbing gritty roads in the Colorado mountains. The roller wear on a chain with that much use will be much greater. The OD of a roller may be .005 inch smaller and the ID about .010 inch larger. The space between the rollers may increase from .200 inch to .240 inch. The side clearance, will also have increased to around .013 inch, or about twice the original amount. The bottom line is that the chain was totally shot, even though the elongation was small. In this case, measuring elongation properly - with a full length measuring tool gave the idea that the chain was in good shape, when it was not. Most other brands would have elongated into the .75-1% range with that much use.

Flipping a chain is thought to increase chain life because the wear is not centered over a 180 degree arc with endpoints that are perpendicular to a line through the pin centers. When a chain is flipped, a little of the unworn pin area is being used. Flipping a chain does not change the wear area by 180 degrees, from the back of the pin to the front.
Roller wear is not a factor in the life of the chain unless you get them so thin that they fail. By then everthing is shot.
I had a 7sp. Taya chain last over 16k miles. I remove and clean mine every 650 miles.

too much trouble for me -- especially since I don't even do any maintenance on my chains.

Roller wear is not a factor in the life of the chain unless you get them so thin that they fail. By then everthing is shot.
I had a 7sp. Taya chain last over 16k miles. I remove and clean mine every 650 miles.

You're wrong about that and your example if about 25 years out of date. I rode 7 speed bikes back in the mid 80's. In the case of the Campy 10 chain with 6,000 miles on it, the roller wear caused enough wear to the cassette that it would no longer mate with a new chain. A new chain skipped on the most-used cog. If the chain had been changed out earlier, then the cassette would have worked fine with a second or third new chain.

Also, everything else on the chain WAS shot at 6,000 miles. I'd never run another one that long again.

If you really want to get the most from a cassette, alternate the use of 3-4 chains and change them out when about half worn. Never let the elongation exceed .5% before alternating and in the case of a Campy chain don't let the roller spacing go beyond .220 inch before alternating (since elongation will not reach .5%). The cassette will last the entire life of all the chains and never suffer from new-chain skip.