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Bio-lubricants: Fast or Friction?
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Posted By: Mason Copeland
Aug 26, 2021
NSMB: 2-Minute Expert
2-Minute Expert is an NSMB series that distills technology and other concepts into short, easily digestible articles.
If you're anything like me, the sound of a dry chain is like glass shards being ground into your ear drums. It's hard to hear someone's drivetrain being powdered, and it's so easy to fix the problem. We all know it's important to keep our chains lubed, but...why? I had a discussion with Isaac and Alex Marangoni, the father and son team behind Whistler Performance Lubricants (WPL) to learn about how lube works, how to choose the right lube for your type of riding, and what they're doing to develop and market bio-friendly lubricants. And despite my best efforts, this article will take closer to five minutes to read than two - but unless you studied chemistry, you'll probably come away with a much better understanding about lube, as I did.
Why Do You Need to Lube Your Chain?
Safe to say that all of you reading this understand that a well-lubed chain is vital to a properly functioning bike. But for the sake of your buddy with a dry chain and selective hearing that you're going to send this article to once you're done reading it, let's recap. There are two very important reasons to keep your chain properly lubricated:
Efficiency: A well-lubed chain will transmit more power from your legs to your wheels, thanks to a smooth-running drivetrain.
Durability: Lubrication will prevent premature wear. This becomes even more important when riding in adverse conditions - dust, dirt, sand, and water all want to tear into your drivetrain like a troll in the comments section of an article behind a paywall. And it's doubly important when you consider the cost of a modern high-performance drivetrain.
Any lube is better than nothing, but sometimes a wet or dry conditions specific lube will last longer and work better - or at least require fewer refreshes and less cleaning.
Nothing surprising there. What I find much more interesting is the why. The best way to understand what's going on with lube on your drivetrain is to discuss the Stribeck Curve. Here's where we start to get a bit nerdy.
The Stribeck Curve
A lubricant's job is to decrease the coefficient of friction between moving surfaces (what we called efficiency above) and help dissipate heat, and it also needs to stay in place on the metal under high loads, because if it's removed, it obviously can't do its job anymore. Other than the obvious impact on efficiency, lube that goes AWOL will also lead to premature wear. What I didn't know before was that the relationship between lube and the metal it protects changes based on speed, load, and and lube viscosity, which is a function of temperature. This relationship is characterized using the Stribeck Curve, which can be used to chart changes in the coefficient of friction as a function of the Hersey number, which is equal to viscosity x sliding speed/normal load per unit length). Forgive the complexity, but the upshot is that there are three basic states that can describe the relationship between lube and the metal it's been applied to:
Boundary: this state describes a low speed/high coefficient of friction whereby the lube provides a protective barrier at a molecular level, which is the only thing preventing metal-to-metal contact, and ultimately damage. Think of this is the state of your engine when it is cold - or your drivetrain before you start pedaling.
Mixed: also known as 'thin film' or 'elasto-hydrodynamic' regime, this is when a thin film of lubricant develops as a result of motion and flow in between the surfaces. Higher speeds lead to greater film thicknesses, which decreases the coefficient of friction to a certain point after which the increased drag of a thicker film increases the CoF (ie. good protection of the moving parts but a lower degree of efficiency).
Hydrodynamic: the thin film from the mixed state becomes thicker as speed increases, requiring more power input for a given level of output. Put a different way, a purely hydrodynamic state is less efficient and therefore sub-optimal for cycling (and most other applications).
...Checkout the full article on NSMB here.