Broken Bicycle Chains

Introduction

I broke two bicycle chains during work in the year 2024. I found this a little bit odd and tried to determine the reasons for it. Here in this text, I will try to write about what I learned until now simply, without getting into too much technical or scientific explanation.

We are using simple, sustainable, considerably durable electric bicycles with seven inner-hub-propelled gears. So, is it the maintenance problems (which we are terrible at – no time is defined for that)? The lightest models of bikes we are using are 22 kilograms, so is it too heavy for the chain quality they are using? Am I implying too much power as I’m not feeling the exact power I’m transferring to the chain? Is it how I cycle? Is it something else that I couldn’t think of? Or is it just a combination of some of these reasons? Is there a connection between problems of chains and problems of shifting gear?

As you can see, there are lots of questions, if not more, to answer. To do that, I will first try to explain bicycle chains in a general term. The next phase will be compiling the most common reasons for chain failures, then comparing these reasons and correlating them with our daily work, and finally, trying to conclude the text with some suggestions for this problem.

The Chain

I believe the best way to analyze the incident of breaking a chain is to begin by briefly explaining a bicycle chain.

Chains are a part of drivetrain systems in bicycles that are responsible for creating mechanical advantage via gears and cogs as such. Creating mechanical advantage is mainly the responsibility of cogwheels in different sizes and usually in one of two options. In option one, this could happen via cranksets, front derailers, chains, cassettes, rear derailers, and jockey pollies. In the other option, the cranksets, chains, and inner hubs are establishing the drivetrains. In both these systems, chains carry the movement from the center of the crankset to the back wheel.

A chain contains lots of links that create empty spaces or gaps in between connection points that stand vertically to take the cog tooth in. In this position, a chain can stand straight when slightly tensioned, bend around a cog, and have a small amount of slack to the sides which helps to shift the gears. Finally, both ends of the chain are attached to create a big loop that we define as a chain in the bottom of a bicycle between the crank and the back wheel. It takes the rotational movement from the crank that we create through paddles, transfers horizontally to the back tire, and with the cassette/cog in the back tire this movement shifts to rotational movement again and turns the tire. This is a pretty basic description of a bike chain but it would be enough in this stage.

If we look at it in more detail, one little chain loop consists of four elements: outer plates, inner plates, pins, and rollers (bushings). Inner and outer plates are on both sides of the chain, pins connect these side elements, and rollers are placed around the pins. In this structure, side plates can rotate around pins, making it possible to bend around cogs and the gaps between rollers are where the cog teeth are inserted. As it is obvious now, while rollers smoothen the pulling effect of the cog tooth and keep the distance between two sides of the chain stable, the main load-bearing pieces are the pins in this system.

The distance between pins is called the “pitch” of the chain, and even the most common pitch is 12.7mm. (1/2 inch), It’s a shifting value that is determined by the number of gears. Lots of materials like steel, stainless steel, alloy Steel, brass, aluminum, bronze, copper, and plating materials like nickel or zinc can be used in the process of chain production to get a durable and sustainable product. Almost all around the world, the accepted minimum tensile strength for a bicycle chain is 8 kN, except for Germany which accepts 9,2 kN as the minimum tensile strength. These are only the minimum amounts, so it is possible to say that they are produced somewhere between 8-10kN in general.

The Most Common Reasons for Breaking a Chain

As it can be a cumulative consequence of different conditions, it might not be possible to determine the exact cause of a chain breakage. Before getting into the details of bikes in general and the problem of breaking chains, I would like to begin with a basic introduction to e-bikes.

E-bikes and Mechanical Advantage

Gaining mechanical advantage is one of the main concepts of bikes. Practically, it means that the cycler uses only some “reasonable” amount of power to be able to ride steep places, gain speed cover a long range, etc. This type of energy conversion happens in the cogwheels and gears. When the cycler feels that it is too difficult to climb a steep place, he or she lowers the gear to soften the paddling and paddles more, cycling less distance but with more ease. In this equation, the cyclist is more relaxed and most of the stress is on the gears. Now imagine the same condition but this time the cycler doesn’t feel the stress as he or she would feel on a normal bike. No need to lower the gear too much, and still be able to climb faster. This is an example related to e-bikes. They ease the movements of a bike. The only problem in this situation is that the excessive strength will be on the gears and will be much more than the normal bikes. In other words, e-bikes add extra load to drivetrain systems.

Here in this section, I tried to collect and compile the main reasons for breaking bicycle chains regardless of e-bikes or normal ones.

Tear, wear, and Rust

When not properly cleaned and lubricated, chains and cogs collect all kinds of dirt and particles on them. These particles collected by the excessive oil in the system damage the drivetrain (especially chains and cogs). In addition to this condition, chain links develop elongation over time, called the stretch of chains. When this condition is realized, the tensile strength of chains decreases, and as the position of chain links does not match the cogs, they damage cog tooths also. About 1% of elongation means 15% weakening in the tensile strength of the chains.

Another typical (and similar) problem is rust that can develop in the drivetrain system together with other parts of the bicycles. In this problem, rust eats the links of the chains and weakens them.

Sudden Impact

Damaging only one pin is enough to break a chain, and sudden impacts can also break them. This fact is significant for mountain bike riders, prone to falling or hitting the bike into obstacles like rocks, trees, etc. much more often than road bikers. On the other hand, accidents, falls, or careless riding make it a problem for all types of cycling.

Failure in Maintenance

Many of the problems defined in this text can be prohibited, solved, or diagnosed early by applying maintenance for bicycles up to a level.

All vehicles require maintenance, and at this point, we should remember that bicycles are also vehicles, amongst other things like “fun,” “hobby,” and “sport”. This would mean creating cleaning and maintenance schedules, defining time requirements, defining maintenance levels, providing basic training, etc.

Failure on Installation

If the chain is not installed properly, it will cause extra stress on the chain links. Even if the reported problems related to this problem are pretty rare, chain installation requires trained hands.

Failure in Production

This is also a relatively rare problem that a cyclist may experience, but as a rule of thumb, high-quality chains are known to be less prone to this problem.

Our Bicycles’ Working Conditions

Up to this point, this text was about providing general information related to chains and some common reasons for breaking them. At this point, I will briefly describe the cycling conditions in my Home Care unit that aren’t required to be the same in all regions in Sweden.

Ownership and Accountability

In our community, we don’t own the bicycles that we use in Home Care; we lease them. This means that a bicycle that we lease stays for three years in our unit and has two free services per year that are usually planned for the tire-changing seasons (winter/summer).

We have support personnel in the units who are responsible for lots of things like ordering materials, the keys, washing clothes, and following up on the accountability of bicycles. Amongst other things, this would include arranging the environment for charging the batteries, managing the keys related to bicycles, arranging some hand tools and pumps in the facility, and arranging the transfer to the services, as such. These personnel aren’t necessarily trained on bicycles in general and/or maintenance of them.

Maintenance

Weather: Our operational region is pretty wet (it rains a lot) and can be cold in winter.

In our unit and our community, there is neither training, defined maintenance levels, nor a defined maintenance schedule. When something goes wrong, we just send the bicycles to the service.

Training of Personnel

Practically there is no defined training program related to the bicycles to the personnel in our community. There was an attempt for a training program once, but as the content was not clearly defined, it was mainly about bicycle types driving in traffic and being careful on parked car doors as such. Even if it was not the desired course program, this was the only course that we know that happened in our community.

The Basic Correlations

At this point, I will correlate the information regarding our bicycle types, general information regarding chains and drivetrains, the most common reasons related to breaking the chains and damaging the drivetrains, and finally the actual conditions regarding bicycles in our community. As this text’s topic is about the chains, these correlations are not going to cover the other parts and topics related to bicycles.

Introduction

We are working in a rainy region in Sweden (west coast), and as we are talking about Sweden, it can be cold in winter too. We are using simple, sustainable, considerably durable electric bicycles with seven inner-hub-propelled gears. Home Care is a healthcare unit where the personnel travels between caretakers with e-bikes. None of the personnel has training regarding the bicycles or basic/minimum required maintenance of a bike. Everything in the job is time-sensitive as there is a very tight daily schedule. They are not aware of the force they are applying to the gears as the main purpose is to go as fast as they can, they do not shift the lower gear unless they have to. There is no defined schedule for maintenance, there is no defined level of maintenance. Almost all kinds of repairs and services are done with the companies according to the agreements, two services per year are free, rest of the services or repairs cost the community.

Some Conclusions

Unlike failures in installation or production, which are mainly caused by service-provider companies, tear, wear, and rust are very common reasons for breaking a chain for Home Care Units as there is almost no maintenance. In this text, I would like to concentrate primarily on these issues.

Maintenance in General

One important advantage of using a bike with an inner hub is that it requires very little maintenance compared to bikes with cassettes and front and rear derailleurs. On the other hand, if something happens to them, only the service points can solve this problem.

All the documents and books related to bike maintenance define four levels of maintenance:

 

• Daily Inspects

• Weekly Maintenance

• Monthly Maintenance

• 6 Months’ Maintenance

Practically, we have the six-month maintenance, which is done by the companies that have contracts with the community, and the other intervals are not done at all (or very rare). As no time or personnel is defined and/or trained for these levels, it is impossible to accomplish these phases. When something happens and it happens, we send the bikes to the repair shops, and obviously, this comes with a cost.

Required Knowledge and Skills:

• Anatomy of a Bike
• Using defined list for Maintenance
• Maintenance-related knowledge and skills in general.

Washing the Bike and Chain/Drivetrain Maintenance

In wet climates like we are living in, if it is not waxed (costs more) the bicycle chains generally come from the services as lubricated with wet oils as they should be. As the wet lubs (oils), don’t wear out with the rain and wet, they are the ones that are preferred in wet climates. The main problem with them is sand, mud and all kinds of particles stick on the metal gear in the wet conditions and these particles eat the chain links and metal gears up. If you try to use oil directly at this stage, you would only have more sticky areas and this wouldn’t help the situation. The problem with dirty chains is not only related to the probable damage they are going to cause, but also it requires more energy for the biker to paddle. Dirty chains and drivetrains require primarily, washing the bike, then de-greasing the chain in certain periods, and re-lubricating. Spray oils are not preferred in this process as we would try to keep the brake pads and discs free of oil, and WD 40 is definitely not the right type of material for this purpose.

One other thing that could be mentioned here is measuring the stretch of a chain. It only requires a simple tool and is pretty simple to accomplish. This application will warn the personnel about the possibility of breaking a chain before it happens and save the crankset and inner hub cog from probable damage that will come from the chain whose elongation is over limits.

Required Knowledge and Skills:

• Washing the Bike
• De-greasing the Chain
• Knowing the oil types and their differences
• Lubricating the Chain
• Measuring the Stretch of a Chain.

Conclusions

Here in this final part of the text, I would like to summarize the topics that I wrote above related to problems with the chains and drivetrain.

 

• Depending on the area that we are working in the home care unit, it is pretty normal to cycle 5 to 10 km. or more and usually spend more than an hour on the bike every day. Even if we are lucky enough to be able to cheat this situation with e-bikes, we still need to know and understand the bike that we are using, as each solution comes with its own problems. This requires a short course on the bikes that we are using. General bicycle types can be an additional text or film only for the ones who are interested. Still, every personnel who should ride a bike in the home care services should learn the general specs and characteristics of their bikes.

 

• One reason for breaking a chain is sudden impacts—in our example, this would mainly mean accidents and bike falls. Wind may also cause falls. Only these facts are enough to set up some type of parking apparatus in the organization’s locations. I don’t mean the parking places for the nights, which is obviously necessary, but for the temporary parking like lunch break as such. Note that the same place can also provide an opportunity to set up a stationed tire pump.

• Probably one of the most obvious actions against breaking a chain (and many other issues related to the bikes) is about maintenance. As there is no defined maintenance program in our community out of sending the bikes to the service shops, I would like to begin from the macro perspective first, and then come to the maintenance issues related to the chains and drivetrains.
  
  

   

  • Macro Perspective:
    
    

     

    • Defining the maintenance intervals
    • Defining the tasks for the intervals
    • Measuring the time requirement for each task
    • Establishing/developing the maintenance environment.
    • Preparing media for recording (paper, application, etc.)
    • Training related personnel for these tasks.
    • Recording all issues to a database for evaluation

  • The Chain and Drivetrain Specific Maintenance. Note that this consideration will be detailed after defining the macro perspective. So, here I’m only listing some of the minimum required tasks with no or minimum tool requirements:
    
    

     

    • Cleaning the chains and drivetrains
    • Measuring the stretch of the chain.
    • De-greasing the chains
    • Lubricating the chains.