Shimano CN-7801 chain stretch

[dziehr]

I recently purchased a Park Tool chain checker and measured the Dura Ace CN-7801 chains on three of my bikes. I was surprised to find that each chain, according to the tool, is well over 75% worn despite relatively low mileage. One chain, installed approximately three weeks ago and with 6-700 training miles and one race, is around 75-100% worn, according to the tool. A second chain, treated similarly, measures the same. The chain on my TT bike, with one IM race and a few training rides (approximately 300 miles), also measures around 75% worn. To be sure that my tool is not the issue, I measured the nearly new chains on my sister's (Dura Ace CN-7701) and dad's (Campagnolo Chorus 10) bikes, and both registered at approximately 25% worn.

I am able to change cassettes around without chain mesh or skipping problems and typically replace chains after around 1200 miles. I am pretty meticulous with my equipment; I clean my chains often and apply T9 before every ride. I weigh around 175 lbs and spend most of my ride time "training" (whatever that means), with a handful of races each month. I race, but I don't beat my equipment to death.

I have another Dura Ace chain on order for the bike I ride most often, but am wondering if:

A: The amount of chain stretch I've experienced is normal for my riding characteristics, regardless of chain, or
B: I ought to try a new chain manufacturer.

I have access to Shimano, SRAM, and KMC chains through a shop sponsor. I've been checking out the KMC X10SL gold (with titanium nitride anodized finish "for durability"). I would like to find a chain that doesn't stretch as much as the Dura Ace, but am a little reluctant to change because I've never had a Dura Ace chain break (stretching aside).

How would you approach this matter? Have your Dura Ace 7801 chains stretched a lot? Any word on the KMC X10SL chains regarding stretching or breaking (ideally, if possible, in comparison with the Dura Ace)?

Many thanks in advance.

DZ

[dvs cycles]

The Park gauge will show a brand new DA chain as 25%.
I toss mine when it reads 75% and usually takes3500 to 4500 miles get there depending on how clean and lubed I've kept it.
My experience and I'm sure there will be a WHOLE lot more chiming in any minute. :beer:

[oldpotatoe]

The Park gauge will show a brand new DA chain as 25%.
I toss mine when it reads 75% and usually takes3500 to 4500 miles get there depending on how clean and lubed I've kept it.
My experience and I'm sure there will be a WHOLE lot more chiming in any minute. :beer:

Park chain checkers are very pessimistic. Take a ruler and measure 12 links..1/16 inch stretch, replace. Rohloff chain checker and ProGold one also good chain checker but the Park ones are poor, IMO.

My experience with KMC chains are very good but I recommend least expensive compatible chain and cogset. You gain nothing with lots of $ for a chain, which is a consumable, afterall. Lower end chains work as well, last as long, less $ than pretty gold or silver chains.

[dziehr]

My experience with KMC chains are very good but I recommend least expensive compatible chain and cogset. You gain nothing with lots of $ for a chain, which is a consumable, afterall. Lower end chains work as well, last as long, less $ than pretty gold or silver chains.

Fair enough. But money aside, do the pretty gold chains (e.g. KMC X10SL) wear slower than standard DA chains? That is, are they any more resistant to stretching or breaking?

[John H.]

I recently sold a bike that had about 1 week of riding on a new dura-ace chain. I got am e-mail from the buyer stating that I sold him a bike with a worn out chain (according to his Park Chain Checker).
I told him that I would gladly give him another chain but in the mean time he took it to a shop that said "you have at least 1500 miles left on that chain".
My experience has been that I get 1500-2000 miles out of a chain so the shops adivce was spot on.
I do 2 things-keep track of miles, and also pay attention to how it sounds when in my 23 and 26- when it starts to be noisy when in those cogs (even when well cleaned and lubed)- it is time to replace.

[dave thompson]

Fair enough. But money aside, do the pretty gold chains (e.g. KMC X10SL) wear slower than standard DA chains? That is, are they any more resistant to stretching or breaking?
Sort of unknown I think, too many variables. Everything on the 'net regarding 'which chain' seems to be anecdotal.

As oldpotatoe said (paraphrasing) chain-checker tools are a lousy way to measure chain. The very best, most accurate way to measure stretch is by direct measurement of pin-to-pin distance for 1 foot, or more. The chain-checkers measure distance between rollers, which would include any stretch but also includes any roller wear, chain pin wear and general chain slop.

Actual chain stretch is the most critical and important part of chain/cassette life while all the other factors; roller wear etc., are minor.

Use a ruler, not a chain-checker to for a go/no-go tool.

[staggerwing]

As an engineer, I have real trouble buying into the concept of chain stretch. Wear, yes; chain stretch, NO!

Steel, up to close to the yield point (which can vary depending on alloy, processing, heat treatment, etc.) is a linear, elastic material. It also deforms the same exact way loading as unloading. These specific qualities make steel an excellent choice for many complex mechanisms that need to perform in a very predictable manner.

Take it past the yield point, and plastic (ie permanent) deformation will occur. This point is defined by stress, which for for straight tension, is simply force/area. It pretty much is a line in the sand that you are going to cross/or not cross. And, if it was low enough, every large guy (hand raised here) pushing a low ration up a steep hill would cross regularly.

Put a new chain on, check it via whatever method you desire (perhaps the mentioned Park tool is made to a poor tolerance and would indicate wear on a brand new chain), and recheck on occasion. My experience puts wear proportional to mileage.

[oldpotatoe]

Fair enough. But money aside, do the pretty gold chains (e.g. KMC X10SL) wear slower than standard DA chains? That is, are they any more resistant to stretching or breaking?

No but any modern chain, installed correctly, should not break. Gold is pretty tho, at least until they get dirty.

[Dave]

Also as an engineer, I think most people know that the term stretch comes from the fact that the chain does get longer as it wears, but the additional length comes from wear between the pins and the bushing formed into the inner plates. At .5% true elongation or stretch (as measured with a precision scale), the combined wear is .0025 inch on each pin/bushing.

What some people don't understand is that roller wear has no effect on elongation or stretch, but those tools sold to measure elongation add roller wear to the actual elongation. Rollers don't all have the same OD or OD, so a chain checker will show a Campy chain at close to zero wear when new and a Shimano or KMC to be .25% stretched. That initial false wear must always be subtracted from future readings. Roller wear is many times greater than pin/bushing wear, so after a lot of use, a chain checker becomes even more inaccurate, adding roller wear to elongation. That can double the reading, so a chain checker might say .75% when the true elongation is only .25%.

Unfortunately, elongation is not the only form of chain wear the damages the cogs so they won't mate with a new chain. I've used Campy chains for 4-6,000 miles and measured .2% or lower elongation, but if only one chain is used for that long with a new cassette, the second new chain may skip on the most-worn cog. My solution is alternating the use of 3-4 chains so none are left in use for too long at any one time. That prevents new-chain skip and allows each cahin to be longer because they are not being thrown away in an attempt to protect the cassette from new-chain skip. I will use each new chain for 1500-2500 miles or until the roller spacing increases by about .015 inch before rotating to the next chain. If you get the last new chain in use without skip, you will never get chain skip for the remaining life of all of the chains.