Some potential solutions to drivetrain wear

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What can be done to reduce the rate at which a bike's chain and sprockets wear out?

An engineer at Renold chains once told me that there are only three factors which significantly affect the rate of chain wear in a typical industrial application: dirt, lack of lubrication, and over-tension. All three of these are present in almost every standard, modern bicycle drivetrain. This article will assess the specific causes of these problems, and suggest several possible solutions, both from a fundamental design or engineering perspective, and simply in terms of what the average bicycle user can do on a day-to-day basis.

 

The Problem

Some of the problems with a part-worn chain include: reduced drivetrain efficiency; increased risk of chain breakage; and passing the "point of no return" (after which the chain alone cannot be replaced, and all sprockets and chainrings must also be changed). But the real problem with a severely worn drivetrain is that the chain will slip when pressure is applied to the pedals, causing them to jump forward alarmingly. The only solution then is to replace the entire drivetrain. See the "Chain Wear" section of our Long Term Maintenance tip sheet for more information.

 

The chain wears surprisingly rapidly on a modern derailleur-geared bike. We are now at the point where, on a typical 27-speed bike which is regularly used in wet and dirty conditions, the chain must be replaced every few hundred miles if sprocket wear is to be avoided; or alternatively the entire drivetrain must be replaced after as little as a thousand miles. Even on a well-maintained bike used in relatively clean conditions, a typical modern chain will not last more than 2,000 miles or so.

 

The Causes of the Problem

Lack of chaincase

The absence of a chaincase on almost all modern bikes means that the chain runs completely unprotected from rain and dirt. Dust, mud, water and road dirt are thrown up by the wheels, and this gets in between the links of the chain, gradually wearing away the surface of the rollers, bushes and pins. The use of oil is essential to lubricate the chain yet paradoxically it also makes the situation worse because without a protective chaincase, oil attracts dust and dirt and mixes with grit to form an abrasive grinding paste which is carried into the links of the chain, accelerating wear. The temptation is to use less oil, but this leaves the chain vulnerable to running dry or becoming rusty which in turn causes more rapid wear.

 

 

Increasingly narrow chains and sprockets

Sprockets and chainrings used to be around 4mm thick (for a 3/16" system) or 3mm (for 1/8") until around the middle of the last century. Nowadays approx 2mm (for a 3/32" internal chain width) is the norm, and even narrower 10- and 11-speed systems are becoming common. And modern sprockets are narrower still in many places because of cutaway shifting ramps and fancy tooth profiles to ease gear changes. These provide nice easy gear changes and permit the use of indexed shifters, but at what cost? With the same pedalling forces being exerted on a narrower surface area, wear rates will be faster, assuming all else is equal. Sprockets and chainrings are now so narrow that it is not uncommon to see a certain amount of metal deformation on the teeth - not from wear, but from instantaneous damage due to heavy pedalling forces.

 

Because modern cassettes have so many sprockets packed into the same space, modern chains must be correspondingly narrower: the outer width of a vintage 3/16" chain was typically 12mm, and even a 6- or 7-speed 3/32" chain was until the 1970's or early 80's around 8mm wide; whereas the chains for new 10- and 11-speed cassettes have to be less than 6mm wide. This can only be achieved through the use of narrower side plates which wear much more quickly.

 

 

Swaged bushing chains have replaced genuine sleeved bushing chains

Originally bicycle chains, along with all conventional industrial chains, were of sleeved bushing roller design with a pin, a separate sleeve bush, and a roller in each link. The advantage for longevity of this system is twofold: firstly, the sleeved bushing is relatively well sealed and therefore remains clean and lubricated; secondly, the entire assembly is stiffer and wider, meaning that when the chain is in tension the force exerted on each link by the previous one is evenly distributed along the whole length of the sleeve and pin. However, with the advent of derailleur-geared bikes with ever larger numbers of sprockets, the quest began for a chain with less lateral stiffness to improve shifting between gears. Additionally, the sleeved bushing chains were potentially no longer strong enough in tension (thanks to being narrower; having narrower 'flush' pins; and due to higher chain tensions because of ever-smaller granny rings). So the swaged bushing chain was developed, and initially appeared as the Sedis Sport chain in the 1980's. Gear shifting was improved (Sedis Sport chains were originally sold as an upgrade to improve gear changes on otherwise unchanged drivetrain components), but the price was a shorter life span: firstly, oil leaks out of the gap between the two swaged 'bushings' and dirt gets in; and secondly the swaged bushings are narrower and can articulate laterally independently of each other, quickly wearing two little grooves into each pin, thereby causing a worn and 'stretched' chain.

 

Modern chainring designs

In the last decade or more there has been a trend towards reduced chainring sizes. Whereas double chainsets used to typically have e.g. 42/53 teeth, nowadays compact chainsets have 34/50. Similarly, old triple chainsets were 30/42/52 or 28/38/48, whereas modern compact triples are often 22/32/42 or similar. Not only has the reduced size of the inner chainring led to a demand for chains with higher tensile strength (with associated longevity problems, see above), but also the generally reduced size of all the chainrings (and correspondingly smaller sprocket sizes at the rear) means that in any given gear ratio, the chain runs at a higher tension, thus accelerating wear. Compact chainsets are slightly lighter, but is this really worthwhile?

 

The search for ever-lighter bikes has also led to the increased use of aluminium for various components, but as always there is a trade-off, and in the context of the drivetrain this means reduced longevity. Aluminium is a much softer material than steel, and aluminium chainrings consequently wear faster than steel ones. Because chainrings wear less quickly than rear sprockets this is sometimes an acceptable trade-off if weight is of prime importance. Unfortunately a few manufacturers have at various times stooped as low as producing aluminium cassettes. These do no last 5 minutes if subjected to real-world use.

 

 

Design / Engineering Solutions (or How it should really be fixed properly!)

 

Derailleur-compatible sealed chaincase

The transmission on a traditional single-speed or hub-geared bicycle was normally enclosed in a fairly well sealed chaincase, which in some cases also acted as an oil bath, not only keeping the chain clean but also constantly lubricated. Even with regular use a single chain and sprocket could last for tens of thousands of miles: years or even decades of use. However, it is difficult to see how a modern derailleur geared bike could easily be fitted with a full chaincase - certainly no such design has to date been produced. If such a device could be put into use, it would certainly greatly improve chain life and would also protect the rider's clothes from chain oil, and ensure a more efficient, quieter, and lower-maintenance drivetrain.

 

Fewer gears

A smaller number of individual gears on a derailleur-geared bike would allow for wider sprockets and chain, and therefore a return to sleeved bushing chains, and therefore a longer-lasting drivetrain. And it need not necessarily even mean a lesser range of gears, simply larger steps between them - see also my article on the optimum number of gears.

 

Larger sprockets and chainrings

For the same gear ratio, a larger chainring and a correspondingly larger sprocket will mean lower chain tension. For example, an old-school touring bike drivetrain with 14-36t sprockets and 30/42/52t chainrings can provide not only the same range, but even the exact same ratios as a modern compact with 11-27t sprockets and 22/32/42t chainrings. The disadvantage may be slightly higher weight, but the advantages will be much reduced chain wear (both because chain tension is lower, and because larger sprockets wear less quickly than small ones), and slightly improved efficiency (because transmission losses are greater with very small sprockets compared to larger ones).

 

 

Practical Everyday Solutions (or What we can do to cope with it in the meantime!)

Some advocate strict chain cleaning and lubrication rituals (see e.g. Jobst Brandt and the late Sheldon Brown), but even if they provide the claimed benefits, in reality these are impractically elaborate for most cyclists. However, keeping the chain relatively clean and not over- or under-lubricating it will certainly help to some extent - see the "Chain Wear" section of our Long Term Maintenance tip sheet for more on this.

 

Stomping on the pedals also seems to have a detrimental effect on the drivetrain's lifespan: not only does being in a smaller rear sprocket than necessary mean a higher chain tension, but standing up and stamping on the pedals also causes uneven chainring wear. Changing into a larger rear sprocket and spinning the cranks faster, in a smoother and more circular motion, will be kinder both to your bike and to your knees.

 

Replacing the chain frequently may also be a good option on some bikes but (depending on the cost of replacement) you may eventually end up spending more money on chains than it's worth!

 

Or you could always find a nice old 10-speed bike with, for example, a Maillard freewheel and sleeved bush chain and use this as your regular high-mileage commuting bike.




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