Chain wear.

14 12 2014

It could be argued that the chain is the single most important component of a bicycle. In some ways, other than the presence of two wheels, it is what makes a bicycle a bicycle. The chain transmits drive to the wheel from the pedals.

Abused and poorly understood, it bears some examination.

On an off-road bicycle, the chain is subject to both mechanical wear from use and the abrasion caused by dirt and water.

Chains on modern bicycles are marvellous. They measure only a few millimetres wide (Shimano 10 speed chain 6.2mm), yet they work exceptionally hard and (at least in the case of Shimano) are highly durable.

The chain and sprockets are designed so that the rollers match the shape of the teeth and the valley between them – when meshed the contact surface area between the two are maximised. This is ideal for the transmission of drive force and minimising wear. They have a pitch of 1/2″ or 12.7mm – this is the distance from one roller to the next.

Chains do not stretch. But with use, the rollers, pins and bushings wear. This allows elongation beyond the 12.7mm pitch and the wear of the chain, rings and sprockets increases exponentially. It is the pin wear that has the most effect. The teeth on the rings and sprockets are slightly triangularly shaped, which means the distance between drive side surface areas of the teeth is slightly greater at the top of the tooth compared to the bottom. When all is ideal, the roller sits at the bottom of the valley between the teeth, but with wear, the rollers ride higher on the teeth, there is less surface area in contact and thus the increased rate of wear and friction.

The solution is to replace your chain often. The magic number is elongation of 0.5% requires replacement. Many years ago, one of my favourite cycling gurus, Charlie Cunningham, wrote a piece on drivechain wear that stuck in my head. In essence, with frequent chain replacement and scrupulous lubrication, the rest of the drivechain will last a long time, even in muddy conditions.

I have owned and used numerous ‘chain checkers’. These tools make the process of checking chain wear quick and easy. To be fair, even using a ruler is quick, but it is also open to user error and I’ll admit I like the replace: yes/no binary answer a good checker gives. Most are placed on the chain in such a way that they push two sets of pins/bushings/rollers apart in order to measure the % elongation of the chain over a certain number of links. We are most interested in pin wear and tools that work in this way include roller and bushing wear in the result. As such, the checkers are designed to give a fairly conservative assessment so that you do not end up using a chain for too long and causing tooth wear. But it is inaccurate.

Shimano make two checkers. The TL-CN41 and the TL-CN42. I have the latter and it works to push the two sets of pins/bushings in the same direction and thus gives an accurate pin wear measurement. It is easy to use and although it is relatively expensive, it will save you money in the long term by prolonging the drive chain life.

The following resources were invaluable in learning about chain wear:

Chain wear measuring tools.

Sheldon brown: chains

63xc: fixed gear chains 101.

Peter Verdone: when to replace chains.

Charlie Cunningham’s (new) site can be found here. It has details of some of his builds – fascinating!

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9 responses

20 12 2014
zippyonline

I think you mean “0.5%” and not “0.05%”! Just so happens I was looking into this yesterday.
Another tool for consideration after my research yesterday is this: http://www.fbchain.com/chain-wear-gauge
I intend measuring chain wear once a week for the period of a few chains over the course of 12 months on the high mileage commuter bikes (i.e. min 100 miles a week all weathers) to track chain wear! When I er get round to changing the currentlt knackered full drivetrain which I reckon is well over 2% stretch…must measure to find out. I am swapping between 2 chains every week though…

Anyway, interesting post, thanks for adding a bit more information into the mix 🙂

20 12 2014
velopest

Argh! Thanks for pointing that out! I guess 0.05% might be a wee bit over cautious on replacement eh? Thanks for prompting the edit!

21 12 2014
zippyonline

Me again! Could you please measure you’re shimano tool, and let me know at what point it reckons the chain needs replacing? I haven’t been able to find this information on the internets.

23 12 2014
velopest

Will do… It will need a bit of thought as the teeth are sloped and so where I measure would be critical. I have a chain that seems to be just in the elongated bracket- I might be better to measure that and infer the percentage, as it does not come up as elongated on any of the other tools I’m guessing it’s pretty accurate to do that? More later…

8 01 2015
velopest

@zippyonline well, there’s more. with a brand new 10 speed xtr chain, the TL-CN42 can sort of be ‘forced’ to show it as worn out. i have a TL-CN41 coming and will come back to all this. i measured 10 links of the unworn chain and it showed no wear, measured with a vernier gauge, obviously, yet the TL-CN42 slotted in if pushed. if ‘rested’ against the link it did not. what this made me think is that with a 0.5% elongation and only using a few links, it might well be *how* you use a device is as important as *which* device. more to come…

30 07 2015
Triangle

Hi. Does Shimano mesure 0.5% or 0.75%. I cant find that info anywhere.
Thanks

1 08 2015
velopest

i dont know the answer to that. it is either ok, or not ok. the tools seem to quite easily be forced to measure ‘not ok’ on even very slightly used shimano chains so i am guessing they use a small percentage wear, perhaps the 0.5%.

10 01 2015
zippyonline

Interesting. I’m going to be delving into this a bit more in the coming months, involving some reasonable miles and weekly measurements for ermm interests sake! I’ll be getting one of these in a bit: http://www.chainweargauge.com/chain-wear-gauge/how-to-use-your-fb-chain-wear-gauge for some easy but accurate weekly measurements!
I’ll share what I’ve found out once I’ve made some meaningful observations.

14 01 2015
Vik

My plan is to generally buy the cheapest SRAM chains for my bikes….many of them run $16CDN 8 spd chains and replace them frequently….once or twice a year depending on mileage. I usually have a need to break a chain and at that time I’ll consider replacing it unless it’s fairly new.

Doing that I rarely have to replace the rings or cogs.

I also can’t recall the last time a chain broke on my bike.

I don’t do proper chain cleanings either. I just relube and wipe down quickly.

We have moist conditions here in the PNW so my bikes see lots of wet and dirt.

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