Gear
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Tech FAQ: dead e-bikes, dumpster diving, and chain stretch measurement

Why to use a chain gauge to measure bicycle chain wear, when you can use a ruler instead.

Have a question for Lennard? Please email us veloqna@comcast.net to be included in Technical FAQ.

Dear Lennard,
I bought an ebike 48V from a guy that lives 1,000km from me. I use the bike on the beach for fishing. My problem is I get an P5d fault when I switch the bike on. When I press the middle button to start the procedure, it goes to O5; everything else comes on, but below the battery status an error is displayed, and nothing else moves. The controller has 5 buttons: middle, east, west, north, and south. I never received a manual, and the seller is very evasive on contact. I bought this as a new Fat ebike. And by the way, I’m 71 and used it only twice on the beach.
Could you please help?
—Charles

Dear Charles,
I am not familiar with this system and don’t know what to tell you.

I’m posting your letter in case any readers out there have an idea of how to fix your system; if somebody writes in with an idea, I’ll let you know.
―Lennard

Dear Lennard,
Good on you for asking the guy WTF he was going to do with a fork he found in a dumpster?!

Back in my shop days, we eventually turned to chopping up anything and everything before tossing it in the dumpster for just this reason. Or somebody would fish it out of there and then bring it in to the shop as a “return” and want his money back.

So, every rim, tire, etc. was chopped or sawed up into pieces that would in no way be useful. One time, a guy returned an odd-ball aluminum rim we had in the $5 as-is, no-returns, blow-out bin. I finally gave up trying to explain the no-return concept and after handing over his $5 + tax, clamped the rim into a vise and sawed it in half!

The guy stared slack-jawed. He asked, “Why did you do that?” and I explained that this had been in the $5 bin for a while, and since it wasn’t good enough for him at $5, it was time to go in the dumpster.

Seemed he would have been very happy to have had it for free…but $5 was just too much. I think he walked out regretting returning it?

With some people you really gotta wonder….
—Larry

Dear Lennard,
Lennard, thanks for the discussion of chain wear. I am using a Park CC-2 and am considering buying a three-point tool. Looking at the photo of the Pedro’s tool, it appears that it has not been inserted according to the diagram on the tool. Does this matter?
—Steve

Dear Steve,
Other than the fact that there is no hand in the photo squeezing the chain upward toward the circled numeral 2 at the right end of the tool, it is installed properly. Here is how you use the Pedro’s Chain Checker Plus. The right end of prong 2 and the left end of prong 1 need to be wedged against their adjacent rollers, as they are in the photo.
― Lennard

Dear Lennard,
Thanks for explaining why 3-prong chain tools are more accurate. What way does the lower accuracy of a two-prong tool cut? Will it recommend replacement sooner or later than a 3-prong tool? My hunch is it will indicate need to replace sooner than a three-prong tool. Also, can I infer from the fact that the lower accuracy of the two-prong tool flows from its inclusion of possible roller wear in its measurement that roller wear does not contribute to chain ring or cog wear?
—Ray

Dear Ray,
Yes, the two-prong chain wear indicator will suggest chain replacement earlier than will a three-prong chain wear indicator. And yes, internal roller wear doesn’t contribute to chainring or cog wear until that wear becomes extreme. Obviously, when the roller actually cracks and even falls off, the chainring or cog teeth pushing on the pin alone create very high wear on the teeth.
― Lennard

Dear Lennard,
Well, I might as well ask. I use a folding rule to measure my chain. 12” rivet center to rivet center is my standard. If it’s more than 1/16” off, that’s my cue to get a new chain. How accurate is that?

Which raises the question, why use a chain-wear indicator when a folding rule is as good or better? And much more useful.

Is it right to change chains when the ruler shows 1/16” too long?
—Scott

Dear Scott,
If the ruler is accurate and you’re careful with how you line it up, that method is very accurate, since you’re spreading it over many links and are not measuring roller wear. When done carefully, it should be more accurate than a two-prong chain wear indicator and possibly more than a three-prong chain wear indicator.

As for why to use a chain gauge when you can use a ruler, one is convenience, at least with a two-prong tool. Using a ruler requires good light, reading glasses (especially when you get into your 60s), two hands, holding one end carefully while looking closely at the other end, and getting your fingers dirty.

Contrast that with plunking a go/no go chain gauge into the chain; it is easier, your hands don’t need to touch the chain, it requires no good light or reading glasses, and many people are more likely to do it because the barriers to doing it are lower. The three-prong tool is more accurate, but it does require two hands that get greasy. It’s still simpler than measuring with a ruler and requires no squinting.

As for how long to check for, 1/16” is 0.0625”, which is 0.5% elongation. Generally, 1% elongation is the point of mandatory replacement, which is 1/8” chain growth, not 1/16”.
― Lennard