Before one can properly select a lubricant for a specific application some basic theory must be understood. When one surface moves over another there is always some degree of resistance to movement. This resistance to movement is called friction. Friction can manifest itself in varying degrees from smooth easy sliding to uneven erratic movement, which can generate excessive heat and cause damage to the moving surfaces.

Friction is good when it causes the brakes and tires on cars and trucks to stop the vehicle or when it keeps our shoes from slipping on wet surfaces, yet friction is bad when it causes heat, wear and reduced energy in an engine, gearbox, transmission or piece of equipment.

Lubrication is simply the use of a material to improve the smoothness of movement by reducing friction. The immediate result is reduced wear and reduced heat generation. There are numerous types of lubricants but for this book the main consideration is synthetic and petroleum motor oils, ATF and gear lubes as related to automotive, motorcycles, recreational vehicles and other equipment.

The coefficient of friction between two moving materials is defined as mu and changes with load and speed. The force needed to start the movement is defined as static friction and is typically always greater than the dynamic friction, which is the force required to keep the two materials moving at the same speed once initial movement has started. Different oils and different materials and loading conditions can create vastly different coefficients of friction that can affect performance and longevity of an engine and other mechanical components. A few basic key functions of a motor oil is to reduce friction under all extremes of operating condition, prevent corrosion of internal engine components and provide for cooling via transfer of heat.

When it comes to reducing friction (as well as preventing corrosion and providing effective heat transfer) I am a firm believer in synthetic lubrication. Here's the basics of why I say that: when using a petroleum oil, under certain conditions, the lubricant film can be either too thin, thus allowing metal-to-metal contact, or too viscous which causes high internal friction within the layers of the oil. The key is to select an oil that is thin enough to have a low internal friction coefficient, yet still high enough to effectively separate two metal surfaces under all operational conditions and prevent excessive wear and heat generation. The facts prove that synthetic lubrication achieves both of these objectives while with petroleum oil there can be a compromise. The uniform molecular structure of synthetic lubricants allow it to flow freely for low internal friction, yet still effectively separate two metal-to-metal contact surfaces under normal and extreme operating conditions and significantly reduce internal wear.

When you look at two metal surfaces, such as piston to cylinder, and visually see that they appear smooth what you are seeing does not accurately reflect reality. When viewed under a high-powered microscope even the smoothest machined surfaces are rough and are viewed as millions of peaks and valleys. These peaks are under extremely high loading and need to wear-in (commonly called break-in) on a new engine. However, there is much discrepancy among automotive and motorsport enthusiasts as to how long of a time period is required for engine wear-in and whether or not petroleum oil must be used for the initial wear-in.

The time required for wear-in, before converting to synthetic oil, on a new production manufactured engine is very minimal and typically occurs during the hot run test at the engine manufacturer and also on the chassis rolls in the assembly plant, while driving the vehicle around the storage yard, railhead, dealers lot and test drives. Babying a new production car for many thousands of miles to "break it in" is no longer necessary, as it was many years ago. There are also a few models of high performance production vehicles that come factory fill with synthetic oil, further verifying the fact that petroleum oil is not required to wear-in an engine.