There are two main reasons.
In the entire bicycle transmission system, the chain can be said to have the shortest lifespan. During the transmission process, the chain will be stretched, the chain links will rotate, and the chain links will come into contact and friction with the teeth, flywheel, and guide wheel, all of which will cause the chain to stretch and wear after a period of use. Therefore, the materials used to manufacture chains require good wear resistance, high hardness, and strong tensile resistance to cope with high-strength usage environments.
Stainless steel, which we believe can effectively prevent rust, is obviously not suitable. Stainless steel is generally low in hardness and brittle, which clearly cannot meet the transmission requirements. This is why bicycle frames generally do not use stainless steel.
Aluminum alloy also has good corrosion resistance and low density, but its hardness is too low and it is prone to wear. Flywheels, tower bases, and the like are made of aluminum alloy, but they are only exchanged for weight based on their lifespan. Just take a look at the marks on the aluminum alloy tower base bitten by the steel flywheel.
But the frame can still be made of aluminum alloy, and there are also some manufacturers who specialize in playing with aluminum alloy.
Of course, since ordinary tool steel has poor rust resistance, we can handle these materials.
So we can see examples of surface treatment for various tool steels, such as chrome plating, nitriding, heat treatment, etc. on the surface of 4130 steel flywheel to prevent rust and wear.
However, we have also seen examples of flywheel coatings falling off in blocks after long-term use, so components such as chains that are more demanding than flywheel usage environments are not suitable for general treatment processes.
So the manufacturer has something like DLC (diamond like carbon). Just understand it as a deposited thin film that combines the properties of diamond and the structure of graphite.
Imagine plating a layer of diamond like wear-resistant and smooth material on the chain, which can isolate the chain itself from the outside world, and solve the two major problems of rust and wear. Although chain stretching is still inevitable, in general, it can be achieved to the point of significantly elongating the chain, and the entire transmission system should be thoroughly cared for.
However, the reason why such a good technology is not widely used is that,
It’s really too expensive.
KMC, a large chain manufacturer specializing in the production of chains, has several top-level chains using DLC technology, with prices ranging from approximately 600 to 900 each.
The same applies to titanium plating.
Of course, there is another way, which is to abandon steel and use titanium alloy to make chains.
Titanium alloy is an excellent metal with both strength and rust resistance, making it very suitable for manufacturing transmission components. The use of titanium alloy in tower foundations, tooth discs, flywheels, guide wheels, and other components of bicycles has long been common in the world.
However, why is titanium alloy not widely used in chain manufacturing?
Because it’s more expensive.
Even a high-quality titanium alloy screw costs more than 10 , let alone components such as guide wheels and tooth discs that require higher machining accuracy and larger volume.
In contrast, currently there are only titanium alloy chains available on the market, and the price of one titanium alloy chain produced by YBN is more than 1000.
That’s why I didn’t mention the titanium alloy chain in the material section.
Well, just take a look.
However, YBN, the manufacturer, is also very conscientious in providing two magic buckles for each chain, which is great.
So ultimately, the reason why bicycle chains use tool steel with average rust resistance is due to the compromise between material and cost. Of course, the latter is more severe.
The reason for rust actually lies more in the fact that most people are too lazy to maintain the chain.
It takes a few hours to thoroughly clean the entire vehicle, including the chain, for a thorough health care.