Societal needs and economic benefits of tribology and lubrication

By Mark Devlin, Contributing Editor | TLT Lubrication Fundamentals March 2026

It’s time to discuss the core technical challenge faced by tribologists and lubrication engineers.

“The danger of a shortage of energy, at least in the form it is traditionally used, is now recognized by all industrial nations. Their Governments have therefore embarked on strategies to effect savings of wasted (or rejected) energy. However, whilst much attention has been paid by Governments to the saving of wasted heat in space heating through insufficient insulation and to thermal cycles of machinery, insufficient thought seems to have been given to the direct and indirect loss of energy occasioned by wear and by friction, and to the savings of materials. Then in 1977, an American government financed report suggested that $16 1/4 billion per annum (at 1976 values) could be saved by a ‘Strategy for Energy Conservation through Tribology.’ Updated to 1981 American values and taking into account the increased world price of oil and American inflation, this figure of saving would now exceed $40 billion a year.”1

This assessment was written by Jost and Schofield in 19811 as a follow up to H. Peter Jost’s influential paper about the economic effects of tribology written in 1966.2 I have highlighted the phrase “the direct and indirect loss of energy occasioned by wear and by friction, and the savings of materials” because this is the core technical challenge faced by tribologists and lubrication engineers. Jost and Schofield’s statement also gives an economic metric in 1981 dollars to justify the need for controlling energy loss. Imagine if we translate those savings to 2026 dollars!! Former STLE director of professional development Robert Gresham, in various TLT Lubrication Fundamentals articles, tracked the benefits of tribology throughout the years, and one can see the value of tribology is well documented.3-7

A convenient construct to understand friction (and wear) in a lubricated contact is the Stribeck curve (I hope you did your homework!).8 The friction coefficient measured between contacting surfaces is plotted as a function of a duty parameter, which is a.) viscosity of the lubricant in the contact zone times b.) relative velocity of the contacting surfaces divided by c.) load applied between contacting surfaces. This parameter is a mixture of mechanical operational parameters (velocity and load) and a lubricant property (viscosity). Furthermore, this duty parameter has the same mathematical form as elastohydrodynamic film thickness (EHDFT) as defined by Dowson and Hamrock.9 This means that the duty parameter is a surrogate for EHDFT. At low values of the duty parameter surfaces are touching and at high values of the duty parameter surfaces are separated.

In most machines when we think about improving fuel efficiency we think about a reduction in friction in order to reduce parasitic energy losses. When surfaces are touching (low values of the duty parameter or low EHDFT) interactions between the surfaces as well as the ability of lubricant molecules to form low friction films lead to improved efficiency. In addition, when surfaces are touching damage can occur to the surfaces (wear or fatigue). This leads to a great cost of money and energy to manufacture a replacement machine for an existing machine that fails prematurely.

When surfaces are separated (high values of the duty parameter or EHDFT), a reduction in the viscosity of the fluid moving between two surfaces will result in a reduction in friction and improved efficiency. Of course, viscosity can be measured under a wide variety of temperatures, shear conditions and pressures, so what conditions are relevant? The answer is all conditions. As expressed in the needs statement from the January TLT Lubrication Fundamentals article, “Lubricants must provide all the functions to cope with the problems of high specific output engines of high pressures, temperatures…. under a wide range of ambient temperatures.”10

The Stribeck curve and the relationship between the duty parameter and EHDFT highlight a critical trade-off between efficiency and durability of a machine. (For a specific example, see the Lubrication Fundamentals article written by Andrea R. Aikin in the July 2021 issue of TLT.11) As mentioned previously, lower viscosity oils provide improved efficiency, but EHDFT decreases with a decrease in viscosity, which could result in wear and fatigue issues. Another trade-off is the effect of temperature and shear on viscosity. A lubricant can be designed to have higher viscosity at high temperature and high shear rates to protect surfaces. However, at low temperatures and shear rates, if the viscosity of the lubricant is too high, the lubricant cannot be pumped to critical parts of machines, and damage can occur due to the absence of the lubricant. In engine oils, this is an even greater concern because starting (cranking) of an engine may be facilitated by electric starters, so pistons and cams are moving even though the fluid may not be pumpable.

Therefore, the lubricant industry has developed specifications defining viscosity grades for different lubricants. Using engine oils as an example, the SAE J300 engine oil viscosity specifications developed by the Engine Oil Viscosity Classification Task Force (EOVCTF) (remember your acronyms) describe the tests used to measure low and high temperature viscosity at low and high shear rates.12 The SAE J300 specifications further define how to label an engine oil to designate the limits for each grade in the various tests. The viscosity of an oil at low temperature and high shear rates, which is related to the ability to start an engine, can be measured using ASTM D5293 (cold cranking simulator or CCS). The pumpability of an oil at low temperature and low shear rates can be measured by ASTM D4684 (mini-rotorary viscometer or MRV). High temperature high shear viscosity (HSV), which can be measured using several ASTM methods (D4683, D4741 or D5481), is the critical rheological property that influences fuel economy and EHDFT formation. ASTM and the Coordinating European Council (CEC) actively monitor the precision of these tests and either improve them or develop new methods, so the methods I have mentioned do not constitute a complete list of available rheology methods.

Oil grades such as SAE 0W20 and SAE 5W30 are shown on the labels of engine oils with the number before the W defining the low temperature rheological properties of engine oils and the number after the W defining the high temperature rheological properties of engine oils. The recommended oil grades for different vehicles are published in owner’s manuals. Similar viscosity recommendations exist for gear oils, transmission fluids and industrial lubricants. In general, to improve efficiency lower viscosity grade oils are recommended as long as they don’t result in an increase in wear or fatigue.

There are cases such as transmissions and hydraulic systems where reductions in friction and viscosity are not necessarily the best way to improve efficiency. Vehicle transmissions take the torque generated by the engine and transfer it to the axles.13 Clutches are engaged and disengaged in the transmission so that different gear systems rotate the axle at speeds desired by the driver. As vehicle speed is adjusted by the driver, the transmission needs to quickly engage different gear sets and make sure they stay engaged. This is a very simplified description of how a transmission works. For the purposes of this article, efficiency is gained in two ways; the transmission fluid 1.) acts as a hydraulic fluid to quickly engage and disengage clutches and 2.) maintains a level of friction so that clutches engage/disengage smoothly and stay engaged. In both of these situations just lowering friction or viscosity to improve efficiency is not desirable. For example, if friction is not held in a specific range, clutches may slip and then stick causing unwanted vibrations in the transmission that can be felt by the driver.14

In hydraulic equipment, the lubricant transmits rotary power from hydraulic pumps to motors.15 The efficiency of hydraulic power transmission is primarily affected by internal leakage flow in pumps and motors (volumetric efficiency) and by friction and viscous drag in the system (mechanical efficiency). Overall hydraulic efficiency is the product of volumetric and mechanical efficiency. Both volumetric and mechanical efficiency depend on the viscosity of the hydraulic fluid. Volumetric efficiency increases with increasing viscosity because thicker fluids leak less. Mechanical efficiency decreases with increasing viscosity because thicker fluids exhibit higher viscous friction and drag. Therefore, there is an optimal viscosity to maximize overall efficiency in hydraulic systems. Finding this optimal viscosity is complicated by the fact that viscosity varies with temperature, pressure and flow rate with flow rate affecting the shear forces exerted on the lubricant.

At this point you are probably asking me to slow down. This article has been a tour-de-force, from the economic importance of tribology and lubricant engineering, to physical properties of lubricants that need to be optimized in lubricants, to tests and specifications the industry has established to measure these properties. I have covered a lot of information, and I have not even started to describe the chemistry of lubricants that influence these critical properties. Be patient—as a chemist I promise to describe lubricant chemistry at a later date. 

I do need to finish this current article by translating the quote I mentioned in the January TLT Lubrication Fundamentals article: “ASTM and CEC have published new methods that the EOVCTF is going to add to the SAE J300 specifications. I wonder if these methods will affect the API specifications for FEI in the VIE?” 

Perhaps you already know how to translate this.

Lubrication engineers benefit society by improving the efficiency of machines with their products. This is evident in improvements in fuel economy in engines. Fuel economy index (FEI) is measured in the Sequence VIE engine test which has been a part of the American Petroleum Institute (API) specifications for engine oils. Viscosity is a key physical property of lubricants that controls efficiency, and ASTM and CEC develop and maintain methods that are used to measure viscosity at various temperatures and shear conditions. The EOVCTF uses the methods developed by ASTM and CEC to define the rheological properties of different engine oil viscosity grades that are described in the SAE J300 specification. OEMs then use the SAE J300 specification (and similar specifications for other lubricants) to define lubricants that best protect and improve the efficiency of their engines and machines.

So, what’s next? The astute reader may have noticed that I mentioned that temperature, shear and pressure affect the viscosity of lubricants. However, I have not mentioned the effect of pressure. In addition, on the Stribeck curve, I mentioned that surfaces can be separated or touching. But what happens when the surfaces are “almost” touching, and only thin oil films keep the surfaces separated? These are the topics I will cover next time. I will touch on base oil chemistry to illustrate several key points, so your homework is a previous TLT Lubrication Fundamentals article written by Dan Holdmeyer describing the processing of crude oils to produce base oils.16

REFERENCES
1. Jost, H.P. and Schofield, J. (1981), “Energy saving through tribology: a techno-economic study,” Proceedings of the Institution of Mechanical Engineers, London, U.K., 195 (16).
2. Jost, H.P. (1966), “Lubrication (tribology) - A report on the present position and industry’s needs,” Department of Education and Science, London, UK: H. M. Stationery Office.
3. Gresham, R.M. (2011), “Who cares?,” TLT, 67 (10), pp. 22-23. Available at www.stle.org/files/TLTArchives/2011/10_October/Lubrication_Fundamentals.aspx.
4. Gresham, R.M. (2013), “Feeling energetic?,” TLT, 69 (7), pp. 30-31. Available at www.stle.org/files/TLTArchives/2013/07_July/Lubrication_Fundamentals.aspx.
5. Gresham, R.M. (2013), “Hey, bud, what’s a tribologist?,” TLT, 69 (9), pp. 40-43. Available at www.stle.org/files/TLTArchives/2013/09_September/Lubrication_Fundamentals.aspx.
6. Gresham, R.M. (2016), “How tribology transformed the 20th Century,” TLT, 72 (6), pp. 38-40. Available at www.stle.org/files/TLTArchives/2016/06_June/Lubrication_Fundamentals.aspx.
7. Gresham, R.M. (2017), “The tribology-energy connection,” TLT, 73 (4), pp. 36-37. Available at www.stle.org/files/TLTArchives/2017/04_April/Lubrication_Fundamentals.aspx.
8. Holdmeyer, D. (2022), “The Stribeck curve,” TLT, 78 (7), pp. 24-25. Available at www.stle.org/files/TLTArchives/2022/07_July/Lubrication_Fundamentals.aspx.
9. Hamrock, B.J. and Dowson, D. (1977), “Isothermal elastohydrodynamic lubrication of point contacts,” ASME Journal of Lubrication Technology, A99, p. 264.
10. Malone, B.W. and Henderson, B.M. (1964) “Trends in engine lubricant development,” SAE 640113.
11. Aikin, A.R. (2021), “Lighter grade oils and off-highway vehicles,” TLT, 77 (7), pp. 32-33. Available at www.stle.org/files/TLTArchives/2021/07_July/Lubrication_Fundamentals.aspx.
12. www.sae.org/standards/content/j300_202405
13. Holdmeyer, D. (2024), “Automotive transmissions,” TLT, 80 (3), pp. 34-36. Available at www.stle.org/files/TLTArchives/2024/03_March/Lubrication_Fundamentals.aspx.
14. Gresham, R.M. (2011), “Slip-stick: What’s it all about?,” TLT, 67 (6), pp. 32-33. Available at www.stle.org/files/TLTArchives/2011/06_June/Lubrication_Fundamentals.aspx.
15. Holdmeyer, D. (2023), “Fundamentals of hydraulics: Pascal’s principle and pump designs,” TLT, 79 (5), pp. 30-33. Available at www.stle.org/files/TLTArchives/2023/05_May/Lubrication_Fundamentals.aspx.
16. Holdmeyer, D. (2022), “Crude oil to base stocks to base oils to lubricating oils,” TLT, 78 (8), pp. 24-28. Available at www.stle.org/files/TLTArchives/2022/08_August/Lubrication_Fundamentals.aspx.

Mark Devlin is a retired chemist and STLE Fellow living in Richmond, Va. You can reach him at markdstle@gmail.com.