Chain Friction Explained

We know there is friction in our chain, and we can use a good chain lube to help minimize it.  Keeping your chain clean helps, but the how and the why of chain friction are largely not understood.  A bicycle chain is seemingly a very simple component when in fact it is an extremely complicated piece of engineering.  Here we will explain what is causing friction, how much, why, how to minimize the friction, and some common misconceptions about chain friction. 

To get a complete understanding of what is causing friction in your chain, we need to take a look at how a chain is actually constructed.  There are 4 different components to make up chains, two inner plates, two outer plates, a roller, and a pin. 

The two inner plates hold the roller in place while the pins are carefully riveted into the outer places.  This means the pin is rotating inside the roller, but the pin is fixed to the outer plate.  The inner plates themselves are then also rotating around the roller and pin.  

As chains have gotten narrower to accommodate more speeds in the drivetrain, they also have to have more horizonal flexibility.  This is achieved by the gaps between the inner plate and rollers and inner and outer plates.  This flexibility is what allows shifting to happen by the chain not having to be perfectly straight the entire time.  While it is great for shifting performance, this can also be a source of friction. 

To understand what is slowing you down on the bike, it is probably just as important to understand what isn’t.  The most common misconception is that the friction is coming from the roller and cassette or chain ring interaction.  This is the metal on metal touching that you can see so it seems as though this is where you need to lubricate to reduce friction.  That is not what is happening at all.  In fact the rollers are so well designed to land in-between teeth on the cassette or chainrings that there is virtually zero friction happening here and requires no lubrication what so ever.  

The roller will drop in that gap and the teeth will pull the chain around and release the roller on the others side of the rotation with almost zero friction assuming that the chain and cassette/chainrings aren’t excessively worn.  This is part of the reason the instructions for most chain lube tell you to wipe off the excess after application.  You don’t want any oil on the outside of the chain.  All this will do is attract dirt and grit that will find its way into the real friction culprit of the system and cause extra friction and extra wear. 

Properly cleaning the chain is a crucial step to reducing chain wear.  When your chain gets dirt and grit in the gaps of the chain, this not only increases friction, but causes the chain to wear much quicker than it would otherwise.  Cleaning with a brush or rag, simply is not going to get into such tiny gaps the way immersion cleaning will.  We have multiple YouTube videos and instructions on how to properly clean your chain.  The two favorites of ours are the Gatorade Bottle method and the Ultrasonic Cleaner Method.  Once we have a chain that is properly cleaned, we can take the next steps to help reduce friction and wear on the chain. 

One of the main sources of friction in a chain is the interaction of the inner plates and the rollers.  In this graph below, we are looking at a cross section of chain.  The inner plates are actually bent on the edges and interface with the roller.  They will rotate around the roller and have a gap about a quarter the thickness of a piece of notebook paper.  This is actually the thing we are measuring when we measure chain wear.  As those two surfaces wear against each other, the chain elongates because there is more of a gap in each link.  This friction occurs every time the chain links bend.  Think every time around the chain ring, both pulley wheels, and the cassette.  This is one of the hardest portions of the chain to clean and to lubricate.  This is also one of the reasons you see time trial specialists in particular use the biggest chainrings they can up front and oversized pulley wheels in the back.  Bending your chain around a 55t chain ring has less severe bends than a 50t chain, that also means you might be in the 15t in the back instead of the 11 or 12, which means it is bending less severe there as well.  Now add a pulley wheel that is 19t instead of a standard 10t pulley wheel, there are again less severe bends.  

Getting this surface clean is more or less impossible without a full immersion clean due to its small size.  Getting lubricant in here is very difficult and why the lubricant’s ability to penetrate these gaps is so crucial.  For wax based lubricants in particular, this is a key distinction.  At SILCA our hot melt wax is an immersive process so this isn’t a worry, but we also offer our Super Secret Chain Lube that was the first wax based drip lube to prove effective at penetrating these types of gaps in a chain by Zero Friction Cycling.  

The inner plates are the surface that rotate around the fixed pin.  A big key to reducing friction here is having these be highly machined to be the smoothest possible surfaces.  A really smooth pin paired with the smoothest possible surface on the inner plate means there will be as little friction as possible.  We also help reduce the friction and wear of this process by adding a lubricant to keep the metal moving on lubricant rather than on other metal surfaces.

Another major source of friction in the chain is the interaction between the inner and outer plates.  As we have looked at in the graphs already, there are gaps in between the plates.  That might lead you to believe they don’t touch.  You have likely heard about chain line, cross-chaining, etc and this is where that can really come into play.  If we are on a track bike, this is likely not much of a source of friction because our chain line is near perfect all the time and the chain is always going in a straight line.  Now when we start to talk about riding on the road, often times we are in a sub-optimal gear when we are looking at chain line.  

The flexibility required of chains is something we touched on earlier.  In order to ride in your big ring and the third to largest cog in the back, the chain needs to bend and that will reduce the gap between the plates causing them to actually rub against each other.  This is a much larger surface area of metal on metal contact than other parts of the chain so it is extremely important to have a good lubricant to stop that friction from happening. 

Here we can see the yellow highlighted portions of the inner plate and outer plate that would be rubbing against each other causing friction in a cross-chain scenario.  

We talked about the importance of how smooth the surface of the pin and inner plates are to reduce the friction between them.  One of the interesting things about materials science is that there is no such thing as perfectly smooth, perfectly round, etc.  Steel chains are rolled steel that is first hot rolled, then cold rolled to get the metal to the specified thickness.  While it looks very smooth to the naked eye, all metal surfaces have imperfections, and we measure them by their peaks and valleys or RZ value. 

Here we see a visual representation of metal after each step in the rolling process where it gets smoother over time, but never perfectly smooth. 

In a chain we see about a 0.6 micron RZ.  This means there is more or less a .6 micron difference between the top and bottom of those peaks on the metal.  The real beauty of wax based lube is that wax will do a great job of filling in those gaps to reduce friction, but when we add Tungsten Disulfide to our lubricant it takes this effect to another level. The WS2 (tungsten disulfide) that we use is about .6 microns as well.  This allows the WS2 to fill in the imperfections of the metal at the same size as the imperfections.  It creates just about the most perfect surface finish possible.  Now the surfaces that are rubbing together are an ultra low friction WS2 rather than two imperfect metal surfaces. 

When we use these friction modifiers like WS2 we are permanently or semi-permanently changing the surface of the metal.  This is the real secret sauce in our Super Secret Chain lube and why our lubricants work so well to reduce friction and wear in your drivetrain.  

As always, we love questions and comments so please leave yours below, watch our YouTube video on the topic, and let us know what we can answer for you next!