Technical FAQ: Chain wear measurement
I’ve been evaluating different methods for assessing chain wear. Maybe you will find the following interesting.
I have a freshly cleaned and lubricated SRAM PC1170 chain with about 1,500 road miles. There are 54 outer links and 55 inner links, so the total length of a brand new chain is 54.5 inches measured between the centers of the holes in the first and last (inner) links.
The five measurement methods indicate:
1. ProGold ProLink Chain Wear Indicator: 85 percent worn
2. Park Chain Checker: 0.5 (50 percent) worn
3. 12-inch steel rule: negligibly longer than 12 inches
4. 6-inch digital calipers: negligibly longer than 6 inches
5. Hanging old next to a new (“uncut”) chain: the old is 0.19 inches longer than to the corresponding link of the new chain
I consider measurement #5 to be the most precise.
0.19 inches over a length of 54.5 inches corresponds to 0.042 inches over a length of 12 inches. 0.042 inches is slightly more than half of 1/16 of an inch and should be good according to Sheldon Brown:
1. If the link pin is less than 1/16-inch past the mark, all is well.
2. If the link pin is 1/16-inch past the mark, you should replace the chain, but the sprockets are probably undamaged.
3. If the link pin is 1/8-inch past the mark, you have left it too long
Thus, I conclude that:
1. The chain is a slightly more than 50 percent worn.
2. Of methods #1 to #4, the Park Chain Checker got closest to the correct result.
Chain elongation, as it is representative of how much wear has occurred at the pins and rollers over time, is the best way we have of measuring chain wear. There are many ways of measuring chain wear, and you mention a few of them. I have, over the years, struggled with this question, consulted with tool brands on the designs of chain-wear indicators, and have measured innumerable chains with many different methods. I have yet to come up with a definitive way to do it. I have ended up choosing one chain checker that I found to be the easiest to use, and I use it frequently and try to figure out its idiosyncrasies to ensure first and foremost that I replace my chain soon enough that it doesn’t fry my cogs, and secondly that I don’t replace chains too soon and throw good money down the drain by disposing of perfectly good chains.
I consulted with Jason Smith, owner of Friction Facts, who has not only taught the entire bike industry much in the past few years about chain friction, but who has also single-handedly brought about the kind of chain preparation and measurement that Bradley Wiggins used in his hour record. He performed a comprehensive test that measured the frictional losses of a chain vs. chain elongation. The results show that friction on average increased at a rate of about 2 watts per 1 percent chain elongation. The test was performed at 250W rider output, so the losses would increase linearly for high-output riders. Yet another reason to keep an eye on chain wear and to replace a chain sooner-than-later if seconds count.
This is what Smith had so say about measuring chain elongation:
“When Friction Facts performed the ‘Effects of Chain Wear on Efficiency’ test, we experienced similar issues regarding accurately quantifying the level of chain elongation on the worn sample chains.
“Each measurement method your reader describes, whether it’s using a chain wear tool, or the ‘ruler method,’ or the hanging method, comes with pros and cons. Chain wear tools are quick and easy to use. However, their accuracy might not be as high as the ruler or hanging method. For reference, this site provides good information on the functionality of chain tools and mechanisms of chain wear. [The Pedro’s Chain Checker Plus chain wear indicator shares the same measurement features with the Shimano TL-CN40 and TL-CN41 tools -Ed.]
“Most popular chain tools introduce some level of inaccuracy because the tool includes the wear of the bushing of the final link of the span being measured. Tool manufacturers can adjust for this additional elongation. But this brings up another point: The accuracies of the tools are based on the tool design itself. A manufacturer can create conservative conditions, or adjust for the bushing, or other dimensional design variances essentially determining the measuring functionality of each tool in order to transform a length into a percent value. Compare this to a high-accuracy metal scale, where 12 inches is 12 inches.
“We’ve used both the Park Tool CC-2 and the ProLink chain tools here in the lab. We’ve found that the Park Tool typically measures about 0.15% higher than the ruler method, and the ProLink typically measures about 0.25% higher than the ruler method. Considering chain and tool manufacturers recommend chain replacement at 0.5% on the low end to 1.0% on the high end, this variance between the tools and the ruler method can be significant when deciding to replace a chain or not.
“Along the lines above, we have found the most accurate method of quantifying chain wear is by removing the chain from the bike, hanging it, and measuring the entire length of the chain (at least 100 links) with a calibrated tape measure. While this method works well in the lab, we realize it is not the most practical method, and much more time-consuming than a chain wear tool. As a compromise, a 12-inch scale can be placed alongside the chain while the chain is on the bike. Yet it is difficult to hold the scale steady against the chain on the front end, trying to read an accurate measurement on the back end, while hoping the scale has not moved on the front end.
“We also have used a method of increasing the accuracy of both the tool and ruler method. We recommend checking the wear at multiple locations of the chain (at least five locations) and averaging the readings. Something interesting was seen when measuring the worn chains for the ‘Chain Wear vs. Friction Test.’ A given chain would exhibit variable amounts of elongation at different measured spans along the length of the chain. It would seem that one link would not be subjected to any different conditions than any other link on the same chain over the life of the chain, and therefore any link would have similar wear to any another link. However, it appears that individual links wear at unequal rates. Of the 10 worn chains we measured for the test, the average differences between span measurements of any given chain was 0.22%. (Note: we used a digital micrometer, not a chain wear tool for measuring.) In the specific chain exhibiting the greatest wear differences between spans, one span measured 0.90% elongation, and another measured 0.42%. If a rider happened to have a chain like this, and check this chain at only one location, the chain elongation amount could be as high 90%, or as low as 42% — quite a large range.
“We don’t believe there is a right or wrong measurement method. In our opinion, chain wear tools are decent methods of roughly estimating chain wear, and especially good for quick go/no-go determinations. A 12-inch scale has the ability to be more accurate than a chain tool, but only if the measurement is performed properly. Yet with either method, to greatly improve accuracy, multiple measurements must be taken.
“A side note regarding the hang-and-measure method comparing a worn chain against a new chain:
“If hanging the worn chain to determine the elongation, we suggest using a scale to measure elongation as opposed to hanging a worn chain next to a new chain and measuring the difference, with the difference being the indicator of overall elongation. Determining elongation by comparing a worn chain to a new chain assumes the new chain is a perfect ½-inch pitch. However, this is rarely the case as new chains are typically not a perfect ½-inch pitch. To demonstrate, we unboxed six new chains of various models and manufacturers, hung, then measured each chain (see photo).
— Jason Smith
SRAM also sells 10-speed 1071 chains after-market with 120 links for 29ers. I think your reader just didn’t find a shop that could think outside the box very well.