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A "chain stretch" question?

Old 09-16-22, 07:50 AM
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Myron
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A "chain stretch" question?

I am in charge of a fleet of adaptive cycles and one of those is a Van Ramm VeloPlus3. It's an adaptive cycle that has a platform on the front for a wheelchair.
The gearing is a Shimano Nexus 8 gear hub. This means that there is only one chain-ring by the pedals and one cog on the hub.

What would be the chain wear limit at which the chain would need to be replaced?

0.5%, 0.75% or 1%?.
I think the maximum allowed elongation is 1%. Am I right or wrong?
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Old 09-16-22, 08:25 AM
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With a way to tension the chain and the large chain wrap around the cog one can very likely ride the chain way past 1% wear and not have a "problem". Chain wear is a gray shade, not a black/white line. Andy
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Old 09-16-22, 08:44 AM
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But isn’t the wear, and need for chain replacement based on the spacing of the links matching up with the teeth on the cogs/chainring? If so, increasing tension isn’t going to correct that spacing. The links would still be out of sequence with the teeth…no?

Dan
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Old 09-16-22, 08:55 AM
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It's really just what is economical for your situation. You have to assess whether you want to replace chains often to save the wear on the rear cog and front ring. Or are you willing to let the chain wear to the point that you might also have to replace the rear cog and maybe the front ring.
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Old 09-16-22, 09:21 AM
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I would rather change the chain and not wear out the tooth on the Shimano Nexus's cog which I can see being more of a headache to change. Because the chain has to tolerate the weight of the rider, passenger and the passenger's wheelchair there is a lot of strain put on the chain so I want to do this right. _ForceD_ I see and recognise the point you're making. A elongated chain is not going to match-up properly with both cogs. What I don't really want to do is replace the chain when it does not need replacing. I want to try strike the right balance.
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Old 09-16-22, 09:48 AM
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If you have a single speed or IGH, there is less chain skipping so the sprockets should wear longer. Plus, the sprockets should be thicker and sturdier than the multi speed sprockets.

I'd get as high quality of single speed chain as you can get. KMC has "E-Bike" chains that are supposed to be very good.

E1EPT
or
Z1eHX Wide EPT (for 1/8" sprockets).

The question for chain longevity will also be overall cost.

So your E-Bike chain will be somewhere around $30. (is that really worth it?)

Your Nexus 8 speed sprocket is less than $10.

You'd also worry about your chain ring if you are hitting high use of the bike.

Overall, the replacement parts aren't that expensive, so it may be easier to push it for a little longer wear.
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Old 09-16-22, 09:54 AM
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Sheldon Brown has a very article about chain wear, its consequences and how best to measure (see 7/8 down on the page) https://www.sheldonbrown.com/chain-wear.html

Note, measuring chain wear with a easy-to-use gauge is not considered accurate, and some style of measuring gauges are better than others. But the best way to measure is with a good ruler. Personally, I like to hang the chain from a nail on a board, and measure vertically (this removing any sag, but requires the chain to the be off the bike).

Since the idea is to save the cog, seems like you want to replace when the chain reaches 1/16" elongation over 12".
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Old 09-16-22, 11:16 AM
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Originally Posted by MudPie View Post
snip

Note, measuring chain wear with a easy-to-use gauge is not considered accurate, and some style of measuring gauges are better than others. But the best way to measure is with a good ruler. Personally, I like to hang the chain from a nail on a board, and measure vertically (this removing any sag, but requires the chain to the be off the bike).

snip
Best way? Subjective at best. Ever hear of parallax? Measuring with a ruler is not a perfect solution. Good gauges work by directly measuring elongation from a baseline. The actual number does not really matter, a go/no-go gauge.
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Old 09-16-22, 12:13 PM
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On a single speed bike it's very reasonable to run chains fully up to 1% (true) stretch. That's 1/8th inch over 12 inches measured pin to pin under enough tension to pull out any slack.

In fact that was in historically the guideline for derailleur chains, and has only recently (my time frame, maybe not yours) been reduced to the current 1/2% beasuse of smaller sprockets and index shifting.

On a single speed, the longer wrap, lower tension (because of larger rear sprocket) and 180 degree wrap, mean slower sprocket wear. Odds are that you could run 5 chains, each to as much as 2% stretch before noticing any issues.

Last edited by FBinNY; 09-16-22 at 09:09 PM.
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Old 09-16-22, 01:23 PM
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I'm not familiar with the Nexus service intervals. But your balancing act will be your hub service intervals. Based on the experience here, 1% or 1/8" is probably a good starting point.

Unfortunately this will take time as you monitor the miles of each bike so you can replace the rear sprocket at "x" miles or "y" service intervals so you are not doing mid-interval sprocket replacements.

If you find that the sprockets are lasting longer, then maybe move your 1% closer to 1.5%.

While not exactly the same as the Honda timing belt and water pump, the water pump was always replaced with the timing belt because the additional cost was minimal compared to the additional labor doing them separately.

John
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Old 09-16-22, 09:05 PM
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Were we astronomers parallax would be important but as cyclists a 12" steel rule works well.
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Old 09-16-22, 09:20 PM
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Originally Posted by easyupbug View Post
Were we astronomers parallax would be important but as cyclists a 12" steel rule works well.
I use a 3' tape measure using the 1" & 37" marks to avoid an error from the "hook".
It's short enough to avoid "parallax" and you get 3X the resolution. A 4' section is too long for me to make sure a chain "end" doesn't shift.


OP, if you are using a chain checker, check the checker.
Mine reads .25% more wear than reality. As long as you know how much error your checker has, it's easy enough to subtract that for a quick, easy check without getting your hands greasy.
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Old 09-16-22, 11:26 PM
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Originally Posted by Andrew R Stewart View Post
With a way to tension the chain and the large chain wrap around the cog one can very likely ride the chain way past 1% wear and not have a "problem". Chain wear is a gray shade, not a black/white line. Andy
This.

Depending on the cost of your front chainring/cranks (and the rear chainring), and other factors, your optimal choice may vary.

Some options:

A) Replacing in time
Replacing the chain at the 0.5% elongation will give you the longest possible chainring life.

B) Not in time, but not waiting for a problem
Grey area between the two extremes

C) Replacing when the drivetrain "gives up"
Replacing the chain when it starts skipping will give you the longest possible chain life (and replacement intervals). But this comes with some notes:
- Severely worn chain will shift poorly with standard derailleurs (not applicable in this case since it's a gear hub).
- Severely worn chain is a bit more likely to break (also less of a probability with a practically singlespeed setup - the gears are all in the hub in this case).

In my experience, for most "casual" cycling, and low to mid-priced drivetrains, the option C is the cheapest.
Yes, chainrings may not last as long, but you swap a lot fewer chains and save there, so the overall cost is a lot cheaper than replacing the chain "on time" - especially if the cranks/chainrings aren't some super-expensive.
In addition to saving costs on chains, it also saves time (a lot longer replacement intervals).

The option A is the safest in terms of preventing problems and providing best possible drivetrain performance (more important with classic derailleurs, i.e. not geared hubs).


This is all without going into any "legal" and "liability" stuff (i.e. whose responsibility is to make sure it all works, what happens if/when a chain breaks etc.).

My long-winded drivel on how to measure wear and when to replace a chain

Last edited by Bike Gremlin; 09-16-22 at 11:29 PM.
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Old 09-17-22, 05:13 PM
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1. The chain on one of these bikes is not going to last as long as a bike with less severe duty.
2. The chain on any bike with a single cog drivetrain can stretch significantly farther than the chain on a derailleur bike.

So: if it's not skipping under load and you can't pull it off the chainring, it's probably fine even at more than 1%... however you want to measure that.

I've seen quite a few of those wheelchair transports on charity rides for MS and Ataxia.
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