The Physics of Fuel Savings

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Release date: 9/12/2018

The Physics of Fuel Savings

When it’s said that “fleet management is a science,” that’s not hyperbole. Specifically, there’s a lot of science involved with motor vehicles, how they can be made more efficient and sustainable, and how costs can be decreased. Having a microscopic understanding of how things work can bring a lot of benefits to your bottom line.

A Force Against Fuel Efficiency – Think, for a moment, about a hand moving through the water, fingers tightly pressed together and cutting in a forward, horizontal motion. Things move pretty fast when the hand is shaped that way. Now, imagine a hand held up vertically as if to say, “Stop,” pushing against the water and experiencing that push-back force. When the subject is fluid dynamics – fluids being both liquids and gasses - it takes more energy to move forward when there is increased surface area and rolling resistance.

This helps us understand inertia, Sir Isaac Newton’s First Law of Motion, much better. It states in part that “a body in motion will remain in motion with the same speed and in the same direction unless it is acted upon by an outside force.” Air is that outside force, pushing against vehicles, diminishing motion.

You could even say that air resistance was strong enough to stop the automotive industry in its tracks in the 1970s. Although aesthetically preferred by many, the big cars of the ‘50s throughout the ‘70s had huge grilles, distinctive shapes, and were made of steel. Their sheer mass – the increased surface area that fought against aerodynamic benefits and significant weight - caused people to say these vehicles “drove like a tank,” and they guzzled gas like tanks, too.  In fact, the 1966 Chevrolet Camaro had one of the worst gas mileages of all time, just over five MPG.
Lessons learned from the 1970s oil embargo and Japanese vehicle downsizing have been adopted by the entire automotive industry, leading drivers to appreciate greater fuel economy while, at the same time, mourning the necessary design sameness required to achieve those MPG gains. The more-streamlined profiles of these vehicles reduce drag and use lighter materials in construction, providing more miles-per-gallon. (A 2018 Camaro with a similar-sized engine hits 20 MPG, by comparison.)

The Science of Fleet Equipment – For fleets that run sedans and small vehicles, a good thing to look into when updating the selector list is a car’s drag coefficient (the measure of air’s ability to “swim” around the object). The more streamlined the body type is, the less drag it will have, meaning less energy is required to push back.

Some vehicles are necessarily going to have a high drag coefficient because of utility. Large vehicles like box trucks and cherry pickers, and semis are, by their very nature, bound to use more fuel. Companies including FlowBelow have developed equipment that fills the gap between a truck’s drive axles. Its AeroKit has a rear panel which acts like an airfoil and helps increase aerodynamics. The OptiFlow SideWing from Wabco uses similar principles to help heavy-duty fleets achieve fuel savings.

All vehicles have other opportunities to mitigate their physics and reduce energy use. Gains made from weight reduction, for example, can easily be lost when equipment is added to a vehicle, or an upfit is not balanced between both the driver and passenger sides of a truck. Equipment should be installed with the same consideration as would be given to cargo, with the weight equally distributed across all four wheels. This is important not only to reduce tire-wear but to reduce tire surface spread.

The more the tire surfaces meet the ground, the more “grab” they will get. This is actually a benefit in slippery conditions like rain and snow, but during normal usage, you are increasing the friction which makes the engine work harder (and drink more fuel). This phenomenon is called “rolling resistance.” Increased tire surface can happen not only in overload situations but also when tires are underinflated – a key factor in fleet preventive maintenance and fuel economy.

Additional savings can be achieved through rightsizing – both the vehicle for the job, and the overall fleet. A vehicle’s utility should be maximized rather than incurring extra costs of unnecessarily large equipment. Additionally, rather than having a quarter of the motor pool not being used, fewer vehicles might be purchased and maintained, increasing their time on the road and producing.

The Science of Behavior – It’s time to take a look at the person behind the wheel.

There are common-sense solutions to some issues of decreased fuel economy. For example, unnecessary idling is equally bad for the environment, for wasted energy, and for the vehicles. Motion automatically assists in cooling mechanisms in a car or truck. Sitting in place while running said mechanisms, on the other hand, will create damaging heat. Further, you’re burning the fuel while doing nothing…a complete waste of resources.

Many telematics systems on the market can be a fleet manager’s eyes and ears in the field, when one needs to know if the driver is hard-braking, doing jackrabbit starts at lights, or any number of persistent behaviors that negatively affect performance and safety. 

Jenny Shiner, Marketing Communications Manager for GPS Insight, stated that telematics and apps could help fleet professionals manage fuel spend in several ways. “The savings an organization can expect depends on a few factors such as fleet size, vehicle type, how many miles they are required to drive, and so forth,” she said. Cutting fuel spend is achieved through “curbing excessive vehicle idling, eliminating unauthorized use of company vehicles on personal time, and improving route efficiency to reduce miles driven.”

A jackrabbit start requires the driver to jam on the gas to get the mass of a vehicle into motion. Tom Kanewske, VP Business Development with Derive Systems said, “The ultimate effect of harsh acceleration is a loss in fuel economy ranging anywhere from 10 percent to 40 percent in stop-and-go conditions or 15 percent to 30 percent at highway speeds (according to the Oak Ridge National Laboratory). Therefore, real-time training and monitoring around proper shifting and acceleration techniques can truly drive marked savings.”

In terms of harsh braking, Kanewske added, “The wastefulness boils down to one simple thing – lost momentum.  By slamming on the brakes, drivers toss away the valuable momentum that could be used to carry them significantly further.  While using roadway friction alone to slow down is not possible, if drivers anticipate stops and only accelerate up until they generate enough momentum to reach that anticipated point, significant savings can be achieved.”

Modifying driver behavior also positively affects safety. If your drivers aren’t gunning vehicles at the green light, speeding, or slamming brakes to avoid running a red light or a stop sign, they’re also less likely to be involved in crashes of their own making. That’s good for everybody.