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Back to Basics: Vehicle Fuel Economy
Critical Elements Regarding Consumption
A TMW Systems White Paper
Summer 2015

INTRODUCTION 1
MPG GAIN MODEL 2
ENGINE EFFICIENCY (BSFC) 3
BSFC MODEL 4
IMPACT: WIND RESISTANCE 6
IMPACT: ROLLING RESISTANCE 6
IMPACT: TERRAIN, DEVICES, FRICTION 7
IMPACT: ENGINE IDLING 8
IMPACT: DRIVERS 8
CONCLUSION 9
SUMMARY 10
SOURCES 11
Copyright © 2009 TMW Systems, Inc. Page 2

INTRODUCTION
With major flux and market volatility surrounding the cost of diesel fuel, complete with
highs reaching nearly $3 per gallon over a sustained period of time, it is crucial that
businesses take full control over variables that are not fixed or dependent upon outside
factors. One solution is to take fuel consumption back to a basic premise of conservation.
Through TMW Asset Maintenance software, businesses can move back to basics without
abandoning the technological advances that are available on the market. In short, the
TMW Asset Maintenance portfolio of products and services blends the best of today’s
technology with basic steps to fully maximize operational efficiencies.
To achieve improved fuel economy requires a basic understanding of the elements which
affect vehicle performance and development of a plan to minimize their affect. This paper
is intended to provide a refresher of fuel economy basics and a discussion of options you
may select to implement within your fleet. A complete fuel management program
generally begins with fuel purchasing and ends with vehicle fuel consumption. Our focus
in this document will be to focus upon vehicle consumption.

MPG GAIN MODEL—WHY SAVE FUEL?
The chart below depicts how small improvements in fuel economy can have big impacts
on your fleet’s annual fuel bill. In addition, fuel savings drop directly to your bottom line
and can be the difference in achieving or expanding profitability.
MPG Gain 100,000 Miles 150,000 Miles
0.1 mpg $1,041/unit/yr $1558/unit/yr
0.2 mpg $2044/unit/yr $3066/unit/yr
1% $627/unit/yr $942/unit/yr
*Calculated using 6.00 mpg and $3.80/gallon US dollars
There are three items critical to determining what fuel mileage you can obtain from your
equipment.
1. How much horsepower you demand from the engine.
2. How efficient is your engine/drive train.
3. Proper vehicle operation by the driver.

Let’s talk about the efficiency of the engine first because it is defined by using the
horsepower component of fuel mileage.
Efficiency of the engine is expressed in brake specific fuel consumption (BSFC). BSFC
is the quantity of fuel (in pounds) required to produce one horsepower for one hour or
lbs/brake horsepower-hour. The lower this number, the more efficient the engine
performs. This efficiency varies in an engine across its speed or RPM range. Typically
the most efficient engine speed is someplace between peak torque RPM and governed
RPM. Therefore when you make a decision about the maximum or cruise speed you
allow the tractor to be driven, your tractor supplier should match the engine,
transmission, and differentials to allow you to cruise in the most fuel efficient range of
the engine. Cruising 100 RPM above peak efficiency reduces fuel mileage approximately
3%. To test how close your cruise speed is matched to peak engine efficiency, ask your
engine manufacturer’s representative to run several simulations using different drive train
configurations. For example, compare an overdrive transmission with 3.58 and 3.42 rear
axle ratios. In addition to fuel mileage considerations you will also need to consider
drivability.
Anytime you make a change to vehicle speed it is important that you understand what
impact the change will make on vehicle performance. As vehicle speed changes, the unit
will now operate in a different portion of the RPM band which may have a significant
impact on fuel economy.
ENGINE EFFICIENCY (BSFC)
Brake Specific Fuel Consumption
0.300
0.305
0.310
0.315
0.320
0.325
0.330
1200 1300 1400 1500 1600 1700 1800
RPM
BSFCLbs/BHP-HR
Chart 1
BSFC MODEL

The impact of speed and grade upon horsepower requirements and fuel economy are
demonstrated in the following table:
Vehicle Speed in Miles per Hour
55 65 75 55
BSFC 0.311 0.311 0.311 0.311
Horsepower 161 229 317 282
Grade 0.0% 0.0% 0.0% 1.0%
MPG 7.69 6.39 5.33 4.39
Table 1
In the table above you can see the increase in horsepower required between 55 and 75
MPH and the decrease in fuel mileage with the same engine efficiency (BSFC). In the
fourth column you can see the impact of a 1% grade upon horsepower requirements and
their impact on fuel economy.
The most significant opportunity to improve fuel mileage in your fleet comes from
reducing the horsepower you demand from the engine. Therefore, it is important to talk
about how we can reduce the horsepower needs in some detail.
Let’s take a closer look at some of the major factors that impact how much horsepower
you will need from your engine. Wind resistance, rolling resistance, terrain, parasitic
devices, and friction all contribute to requiring more horsepower so we will take each
factor and look at them individually.
WIND RESISTANCE: (The law of physics) Number one consumer of horsepower.
1. Every 2% reduction in aerodynamic drag results in approximately 1% improvement in
fuel economy.
2. As speed increases, wind resistance increases exponentially. Speed reduction is a fast
way to improve fuel mileage and was recognized as such when the Federal Government
mandated the 55 mile per hour speed limits on the nation’s highways during the fuel
crisis of the late 70’s. Every mile per hour (MPH) over 55 your truck is driven decreases
the fuel mileage by 0.1 mile per gallon (MPG).
3. Various air fairings and cab designs have been developed over the years to improve the
aerodynamics of tractor/trailer combinations thereby reducing wind resistance. The most

successful has been the roof mounted fairings that have come to be generally accepted by
van carriers. The Society of Automotive Engineers (SAE) has developed a two-truck test
that you can use to test devices under controlled conditions to verify and quantify their
impact on fuel consumption. At a minimum, if considering an investment in these
devices, ask to see results of the SAE testing that was done by a reputable testing agency
(such as the Transportation Research Center) before considering any fuel saving fairings.
Reputable fairing manufacturers have this data. A review can then be performed to
determine if the investment will have an appropriate payback in fuel savings.
ROLLING RESISTANCE: Second to wind resistance in demanding horsepower.
1. An increase in gross vehicle weight from 65000 to 80000 pounds results in a 5%
reduction in fuel economy.
2. The
major
influence
here comes
from the
gross
combination weight of the loaded vehicle. As vehicle weight increases rolling resistance
increases and the amount of horsepower required to overcome the rolling resistance
increases. Specifying light weight components improves fuel mileage but may not be cost
justified.
3. Tires make the largest difference in fuel economy below 50 mph; aerodynamics is the
most important factor over 50 mph.
4. Low air pressure in the tires dramatically increases rolling resistance.
5. Tire tread and casing design impacts rolling resistance. Often there is a tradeoff to be
made between higher fuel mileages (low rolling resistance) and tread life. It is important
to understand this relationship as decisions to increase tread wear can have a significant
negative impact on fuel economy. All leading tire suppliers and re-treaders manufacture
fuel efficient tire products today. With the high cost of fuel it is important that our focus
be on minimizing rolling resistance.
6. As an example, recent SAE testing by Goodyear Tire Corporation demonstrates the
capabilities of today’s next generation tires. Fuel savings potentials nearing an 8%

increase have been verified. Given the impact of other factors such as wind, weather,
traffic and vehicle specifications; expectations of fuel efficient tires will be closer to 4%
in a fleet operation.
*Fuel Max is a registered trademark of the Goodyear Tire & Rubber Company
TERRAIN: It takes more horsepower to go up hill than down.
1. While you cannot affect the terrain where your vehicles may operate, optimizing routes
and selecting conditions where vehicles operate more efficiently is possible.
2. Interstate highways and toll roads offer fewer starting and stopping events and
prolonged periods of operation in maximum fuel economy mode. Careful route selection
can have a significant impact on fuel economy and more than cover the costs of tolls.
PARASITIC DEVICES: It takes horsepower to drive vehicle accessories. Cooling fans,
air conditioning compressors, power steering pumps, alternators; all demand horsepower
which in turn consumes fuel. Maximizing their performance can impact fuel economy.
1. For example, the engine fan can reduce fuel mileage 7-8% if it is left on all the time. If
the fan is on 50% of the time fuel mileage is reduced 4-9%. This is because an engine fan
can take up to 50 horsepower to operate. Specifying a temperature controlled fan and
eliminating manual override switches can save fuel.
2. Specifying a direct drive transmission vs. an overdrive transmission can save 2-3% on
fuel economy. In a direct drive transmission, when operating in top gear, no gears are
turning inside the transmission consuming engine horsepower and burning fuel.
3. Alternators can consume up to 30 horsepower when operating at full output.
Additional lighting, coolers, refrigerators all consume and require electrical power.
While most of these items are essential to driver convenience, maximizing their usage
can save fuel.
4. Rear axle ratio optimization is critical. Specifying one axle ratio lower than optimal for
vehicle cruise speed will result in a reduction of .1 mpg.
FRICTION: Occurs wherever parts rub against each other.
1. Engine oil impacts fuel mileage with multi viscosity and synthetic oils giving
improved fuel mileage.
2. Synthetic fluids in the transmission and differentials reduce horsepower required to
operate.

3. Properly lubricated and maintained trailer axles reduce friction and the horsepower
required.
ENGINE IDLING: While fuel consumption at idle varies between engine
manufacturers, a good industry standard is 1 gallon of fuel per hour at 1000 engine rpms.
1. Any reduction in engine idling is a direct savings to fuel economy.
2. Shutting the vehicle off during lunch/dinner breaks, loading/unloading and during
short rest stops saves fuel.
3. Today’s electronic engines allow you to accurately measure and control the amount of
idle time you allow. Idle controls must allow the driver the ability control cab climate
during rest periods.
4. Idle elimination devices such as generator sets, auxiliary power units, shore power and
truck stop devices can have a significant impact on idling and should be considered after
a financial analysis is performed to determine ROI under your fleet operating conditions.
DRIVER IMPACT ON FUEL ECONOMY: The most efficient drivers in your fleet
will obtain approximately 30% better fuel economy than your least efficient drivers.
To begin a driver fuel management program requires that you can measure fuel economy
on a regular basis and assign the results to an individual driver, tractor and operations
manager. The measurement system employed must be viewed by the driver and manager
as accurate. Once established, regular sharing of performance information with the driver
is critical for success.
Tips to share with your drivers to assist in improving driver performance:
• Setting and maintaining proper or company specified vehicle speed.
• Using cruise control whenever possible.
• Practicing conservation of momentum.
• Limiting the use of vehicle accessories whenever possible.
• It is OK, with today’s diesel engines to turn the engine off even in cold climate
conditions.
• Avoiding “jack rabbit” starts.
• Use progressive shifting techniques whenever possible.
• Reducing the number of stops.
• Limiting engine idling.
• Conducting thorough pre- and post-trip vehicle inspections.
• Limiting tractor-trailer gap.

• Properly setting aerodynamic deflectors.
• Maintaining proper tire air pressure.
Drivers play a significant role in fleet fuel economy. A properly trained and motivated
driver will make a significant impact on this critical cost area. Engine manufacturers are a
good source of training materials to assist in your driver training programs. DVD, VCR
and Audio tapes are all available with specific information about proper operation and
fuel saving tips for the specific engine installed in your vehicle. Make them a regular part
of your driver training programs.
CONCLUSION
Small improvements in fuel conservation can pay huge dividends in the ability to manage
equipment operational expenses. By understanding the “basics” of fuel consumption you
can develop a strategy to maximize fuel utilization. With a focus on the three major
consumption areas listed below and small investments in training and technology, fleets
can achieve an immediate payback for their efforts:
Vehicle:
1. Develop and maintain vehicle specifications to maximize fuel conservation.
2. Properly match drivetrain to operating conditions.
3. Utilization of fuel conserving tire systems.
4. Reduce engine idle by managing idle time and investing in idle alternatives.
5. Manage vehicle speed.
SUMMARY
Outside Influences: Suggested Basic Tips
1. Manage vehicle routes when possible to maximize vehicle operation in optimal range.
2. Minimize stops when possible.
3. Provide a managed fuel network to maintain fuel quality.
Driver: Proactive Steps to Take for Conserving Fuel
1. Train drivers on the basics of fuel consumption.
2. Train engine manufacturer recommended operating practices for conserving fuel.
3. Enlist their support in managing fuel.

4. Consider incentive programs to support driver changes in behavior.
5. Give regular feedback concerning fuel conservation efforts.
SOURCES
American Trucking Association – TMC Recommend Practice Manual
Detroit Diesel Engine Corporation – Brake Specific Fuel Consumption
Cummins Engine Corporation – Guide to Saving Fuel
Goodyear Tire and Rubber Company – Fuel Max Tire Data

Summer 2009
About the Author: Dave Walters holds more than 30 years of experience performing and successfully managing maintenance
operations at industry-leading trucking companies. Walters joined TMW Systems from MaintenanceIO, Bridgestone/Bandag
LLC, where he was vice president of the Fleet Services Division.
TMW Systems, Inc.
Corporate Offices
21111 Chagrin Boulevard
Beachwood, OH 44122

USA
Inquiries:
Phone: 800.401.6682
Fax: 216. 831.3606
About TMW Systems
TMW Systems, Inc., is committed to delivering technologies that help companies in transportation services to seize market
opportunities while improving profitability, asset productivity and their return on information. TMW customers can be found in
trucking, 3PL, private fleet, brokerage, construction, ready-mix, municipal fleet, heavy-duty repair and waste management
sectors. With offices in Cleveland, OH; Durham, NC; Indianapolis, IN; Dallas, TX; and Vancouver, BC; TMW currently serves
more than 1,600 customers managing over 325,000 power units and maintaining more than 1.1 million assets in North America,
Europe, China and Latin America.
Visit www.tmwsystems.com or call 800.401.6682 for more information.
TMT Fleet Maintenance and TMT ServiceCenter are proprietary and service marked software
products from TMW Systems, Inc. Other product and service names referenced herein
may be trademarks of TMW Systems, Inc.
This document is provided for information purposes only and the contents are
subject to change. We disclaim any liability with regard to this document and no
contractual obligations are formed by this document.
Copyright © 2008 TMW Systems, Inc.

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