Secrets of Better Fuel Economy
Contents
1. Secrets of Better Fuel Economy Page 2 of 35 Contents Introduction Understanding Fuel Economy sscsiccicuiatsssaunsasdsouiuiwatnativitincdesdabautiondutinctwemtantys 4 Rock Solid 200 eee eee eee ne een nese ee EE 4 Vehicle Power REGUIRGIMIGNIS sssccesiicnsiraetotonatcnussaclaasanssdeeonaevesassiastavabecnionessasdaoelinspnsdagenusanbilnes 5 Aerodynamic Bl area 5 Cab Aerodynamic Considerations Lu vvavvsvvveenutsdnGaniedand 9 Tractor Trailer Air SG eek 10 Trailer Body KENNEL eee Gamadareaseine et 11 Engine Accessory Drivetrain LOSSES scsssssssssssssessssssssscssseeeesessesssarsseceereesesesseaeas 11 Geah EE EE cetera ta E E 12 Eilola In e E A A 13 Tire Rolling RESISTANCES vsspstsctseccoisstesiudsnrdccrinsensions iesstaauontsdbtenedscdmststuits tunssuioenispeaneebimacsbit 15 Engine Operation and Maintenance cccscssssssssssssssssssessssssessssssesssssssssssseseseseesesesseaean 18 Engine Operating Temperature Coolant and Lube Oil cccsssesseseeeeesseeeen 18 Intake and Exhaust Restriction sceasciccnecs sxiswohusndesssesiscannsmesnsctotuabisielasantesieaubiayedetauecusueis 18 Air Compressor VANN seede 19 Engine Lube Oil LevelS issinsinsiniiiranrinteniinrni riain enii iaa 20 Fan OperatioN ET EE EE TN EE 20 Freon Compressor Operation eee nen 20 PENN 21 Te Inflation PHS SUNG res e 22 Powertrain Guidelines os seats ce tcec bead cde cipal ed lease eee 23 Standard Heavy Duty Gearing Recommendations ceceseessse2. O a SW30 Full Synthetic gt ee a 4 0 15W40 Mineral Base 190 Normal Temp 230 F 250 Oil Sump Temperature Deg F Secrets of Better Fuel Economy Page 13 of 35 The high temperature stability and low temperature fluidity of synthetic lubricants make them ideally suited for drivetrain components In this environment the lubricant is not subjected to combustion byproducts This means the lubricant with its higher oxidation resistance can last substantially longer Drain intervals of 250 000 to 500 000 miles more than offset the higher purchase price of the lubricant Dynamometer and on highway vehicle testing have demonstrated significant benefits in fuel economy Lubrication versus axle and transmission losses 5 JJ Mineral base 5 Synthetic Jf Mineral base Synthetic MPG 7 MPG 7 1 1 70 F 170 F 70 F 170 F Axle Losses Transmission Losses Secrets of Better Fuel Economy Page 14 of 35 Tire Rolling Resistance Rolling resistance results from the internal friction of a tire as it deflects flexes during motion Energy spent generating heat in the tires is energy that does not contribute to moving the vehicle Cooler running tires are more fuel efficient than tires that run hotter Complex rubber compounds advanced casing construction and enhanced tread designs have led to new standards in tire performance Tire rolling resistance is the second most significant contribut
3. 5 Since diesel fuel weighs about 7 1 Ib gal this amounts to a savings of 1 5 gallons of fuel saved every hour 10 5 7 1 1 5 For a truck running 10 hours per day that s 15 gallons of fuel saved per day At 2 45 per gallon of fuel the dollar savings is 36 75 per truck per day Table 1 Comparison of Treatments Aerodynamic Power Requirement hp No Aerodynamic Treatment 145 Full Aerodynamic Treatment 113 32 hp difference MPG advantage assuming 250 hp road load 13 better mpg Secrets of Better Fuel Economy Page 8 of 35 Cab Aerodynamic Considerations Not every truck has to be fitted with all of the aerodynamic features available The list here shows some of the items that can improve aerodynamic efficiency Trailer type and loads hauled in addition to the vehicle speed will determine the effectiveness of a particular item Full Roof Deflector Curved Windshield Fairings Aero Mirrors Sloped Hood Side Extenders Round Corners Side Skirts Aero Bumper Under Hood Air Cleaner s Air Dam Concealed Exhaust System Aero Headlights Recessed Door Hinges Slanted Windshield Grab Handles Fuel Economy Secrets of Better Fuel Economy Page 9 of 35 Tractor Trailer Air Gap To minimize drag resulting from crosswinds and turbulent air tractor trailer gaps should be minimized or aeroskirts should be used to smooth the airflow Beyond approximately 30 inches every 10 inch increase in trac
4. Air Compressor Operation While the air compressor s power demands are small compared with the fan every little bit helps Fixing air leaks can have a small but noticeable effect on mpg Table 4 Air Compressor HP Requirements WABCO 15 2 and 18 7 CFM Loaded Unloaded RPM HP HP 1300 4 0 0 4 1500 45 0 5 1700 5 0 0 6 1900 55 0 8 2100 6 0 1 0 Estimated hp draw with approximately 12 psi manifold pressure pumping to 115 psi Typical air compressor duty cycles approximately 5 and 10 12 minutes between pumping cycles are common The factors influencing excessive compressor operation include the following Air system leaks Air ride suspension Excessive service brake use These can result in a 2 impact on mpg when the air compressor is pumping Secrets of Better Fuel Economy Page 19 of 35 Engine Lube Oil Levels Exceeding the recommended engine oil levels can result in significant oil churning spin losses The effects of these excessive churning spin losses greater than 2 impact on mpg include the following Reduced engine efficiency Reduction in performance Deterioration of critical oil properties lubrication and heat transfer Fan Operation The typical on highway fan run time hits a year round average of 5 7 It takes between 10 and 70 horsepower to drive the cooling fan An inoperative fan clutch faulty thermostatic switch low coolant level or other malfunction that makes the fan run longer c
5. Page 26 of 35 Shifting Techniques Proper operating techniques result in the lowest number of engine revolutions per mile to maximize mpg Constant operation below 1300 rpm significantly reduces fuel consumption Follow two general rules Maximize the percentage of time in top gear Use the full operating range of the engine before gearing down Notice in the following table that the sampled trucks spent more than double the recommended time in 9t gear which resulted in a reduction in overall fuel economy of between 3 3 and 4 5 Taking Truck 2 as an example assume it s running a 10 hour day at around 60 mph and fuel is 2 40 In one year running just that truck roughly 18 of the time in gear down would cost over 1 900 in fuel Table 8 Fuel Economy in Different Gears or What Eg gan to MPG One Gear Down Fuel Economy Summary Eu 1 8 Gear 9 revy Down Gear 10 Top If driven to our Truck ST EA Trip Trip EA Distance Distance Overall MPG Truck 1 4 72 Actual Data 5 60 Eat 11 46 82 94 7 86 MPG 6 86 MPG Cum 9 7 09 MPG Truck 2 SER iad Seco et SL Cummins 6 46 MPG S a 11 74 83 52 7 10 MPG Baseline pote Dat MPG Cummins 2 54 MPG Saving fuel by shifting properly isn t only for the top one or two gears though It works all the way through the gears Load Based Speed Control LBSC allows the engine to adjust the speed available to the driver The ECM looks at the load and sets the rpm limit accordingl
6. ing the powertrain two factors offset each other consideration for the vehicle s performance startability gradeability and cruise speed and consideration for the vehicle owner s desire to achieve fuel economy Lowest Engine RPMs Durability Startability Oil Control Torque Peak Gradeability Cruise Gradeability Spec ing the Powertrain Carefully compare recommendations with current existing equipment Existing equipment should dictate minimum performance requirements Standard Heavy Duty Gearing Recommendations The ideal or preferred engine speed varies somewhat depending on the engine The vehicle should be geared to operate at the manufacturers recommended rpm at whatever road speed the vehicle will spend most of its time The 2007 on highway standard gearing for Linehaul Applications lt 80 000 Ibs at 65 mph is 1450 rpm for ISX engines and 1500 rpm for ISM engines up to 370 HP Above 370 HP for the ISM requires 1600 rpm at 65 mph for improved driver satisfaction Assuming the truck spends most of its time on Interstate highways these recommendations will optimize fuel economy Fuel Economy Heavy Duty Gearing Recommendations The 2007 on highway fuel economy gearing for Linehaul Applications lt 80 000 Ibs at 65 mph is 1400 rpm for ISX engines with a minimum of 1650 torque in the top 2 gears and 1500 rpm for all ISM engines Assuming the truck spends most of its time on Interstate Secrets of Better Fuel Economy Pag
7. speed frontal area and external shape Aerodynamic drag is the most significant contributor to vehicle power requirements above a speed of 50 mph As the following graph shows aerodynamic aids can have a major impact on vehicle fuel economy on an interstate duty cycle and very little impact on an intercity duty cycle 14 12 4 MPG Gain 0 5 10 15 20 Aerodynamic Aid Interstate Intercity Rural Delivery Urban Delivery Secrets of Better Fuel Economy Page 5 of 35 Cummins MPG Guide Go No Aerodynamic Treatment In this case 264 horsepower is needed to over come all of the forces acting on the truck and to keep it rolling at 65 mph Aerodynamic forces wind resistance account for 145 hp over half of the power demand Level Road Power Requirements 0 AERO 145 HP NN TIRE 87 HP 0 MISC 32 HP POWER REQUIREMENTS 65 MPH 264 HP S 500 ENGINE RPM 1450 T 65 MPH I 400 GCW 80000 Ib Oo 300 2 200 z O ou o 0 10 20 30 40 50 60 70 80 90 ROAD SPEED MPH Rock Solid Rule Tires make biggest difference in mpg below around 50 mph aerodynamics is the most important factor over 50 mph Secrets of Better Fuel Economy Page 6 of 35 Cummins MPG Guide Go Full Aerodynamic Treatment Aerodynamic treatments can reduce the horsepower required to move the truck by 30 to 35 horsepower Notice in this example that a vehicle equipped to reduce air resis
8. Minimize use of service brakes plan ahead Vehicle Speed Management The keys to managing the vehicle s road speeds involve maintaining the lowest reasonable cruise speeds possible and minimizing time spent at maximum vehicle road speeds The vehicle s road speed has a tremendous effect on fuel economy As road speed increases so does air resistance and rolling resistance to a certain extent Thus the power required to move the vehicle down the road increases For example at 55 mph you may get 7 mpg at 65 mph you ll get 6 mpg and at 70 mph you ll get only 5 5 mpg In the engine s ECM you can set the Road Speed Governor to limit the top speed of the vehicle Rock Solid Rule Above 55 mph each 1 mph increase in vehicle speed decreases mileage by 0 1 mpg Secrets of Better Fuel Economy Page 28 of 35 Operation in Hilly and Mountainous Terrain In rolling terrain use a light throttle and allow momentum to carry the vehicle over short grades In hilly and mountainous terrain where possible use the engine s entire operating range before gearing down When cresting steep grades use gravity to bring the vehicle back to the desired cruise speed Engine Idling Idle time can significantly affect the vehicle s fuel efficiency Therefore avoid unnecessary engine idling The vehicle gets its worst mpg when the engine runs and the truck doesn t move Every hour of idle time in a long haul operation can decrease fuel efficien
9. Secrets of Better Fuel Economy Page 31 of 35 Appendix A Customer MPG Effect Worksheet Impact Cause Engine and drive line break in effect Tire tread depth effect Running one gear down effect Engine speed proper gearing effect Transmission gear mesh effect Aerodynamics effect Winter effect Cooling fan on time while driving Speed effect Idle time effect Driver variability effect Secrets of Better Fuel Economy After 10K miles the MPG improves approx 2 to 2 to 5 me 5 Customer Special Notes Effect Impact MPG improve by approx 6 from 100 tread depth tire new to a 50 tread depth tire n mm n mm An engine geared to run 1450 rpm at 65 mph gets 4 approx 4 better mpg than one geared to run 1600 rpm at 65 mph If the truck is geared too high it will force a driver to run one gear down See the effect on one gear down in this matrix Transmissions lose approx 75 for each gear 2 to 3 mesh Therefore an OD trans running in OD has 4 gear meshes and would lose about 2 to 3 mpg compared to a direct drive trans Full aero aids can improve mpg by approx 15 0 to 15 above 50 mph Trailer gap must be minimized lt 30 inches Double trailers decrease MPG by 5 _ ne o i that is hard to beat and is based on aerodynamic drag Engines use 5 gal hr at 650 rpm and 1 0 gal hr at 0 to 10 1 000 rpm Reducing idle time from 50 to 25 can improve mpg 2 to 4 Up to 30 difference b
10. an take a big bite out of the fuel economy of the vehicle Cooling system maintenance can have a significant effect on fuel economy Table 5 Typical Heavy Duty Fan Power Requirements RPM ISM HP ISX HP 1100 9 10 1300 14 17 1500 22 26 1700 32 37 1900 45 52 2100 61 70 At 1450 rpm cruise operation the fan being locked on can cause an 8 12 mpg penalty assumes 225 hp road load Freon Compressor Operation Approximately 50 of total fan run time is attributed to the Freon compressor operation Excessive fan operation may result from An overcharged system Defective or incorrect head pressure switches Condenser efficiency Secrets of Better Fuel Economy Page 20 of 35 Axle Alignment Tires need to point straight ahead in order to roll with the least possible resistance A tire that deviates only degree from straight ahead will try to travel 10 to 15 feet sideways for each mile the vehicle travels forward Scrubbing the tires in this fashion is bad for fuel economy and also bad for tire wear This table shows the effect that some tire misalignment has on fuel economy Table 6 Affects of Misalignment on Fuel Economy Test 1 Test 2 Test 3 Test 4 Test 5 Alignment Steer Tire Toe In 0 1 4 1 4 3 8 3 8 Drive Axle Non Parallel 0 0 1 2 1 a Trailer Axle Non Parallel 0 1 2 1 2 1 0 Effect on MPG 0 0 0 6 0 8 1 7 2 2 Secrets of Better Fuel Economy Page 21 of 35 Tire Inflatio
11. cy by 1 Table 9 Idle PTO Fuel Consumption Engine Soeed RPM Average Fuel Consumption Gal Hr 650 0 5 1000 1 0 1200 1 5 Idle PTO fuel consumption increases exponentially with engine speed 0 10 impact on mpg When idling is necessary to maintain cab bunk compartment temperatures select the lowest idle speed possible no higher than 800 rpm Rock Solid Rule Idle time is costly Every hour of idle time in a long haul operation can decrease fuel efficiency by 1 Secrets of Better Fuel Economy Page 29 of 35 Weather and Seasonal Conditions You can t control the weather or the seasons but they definitely affect your fuel economy Running only on sunny days with moderate temperatures is very impractical but you have to take the weather and seasonal variations into account when checking fuel economy Ambient Temperature Air becomes more dense as temperatures drop which increases air resistance For every 10 F drop in temperature aerodynamic drag increases by 2 Thus fuel efficiency will drop by 1 Overall fuel economy tends to be higher in the summer than the winter According to North American Truckload Fleet Data driving in the summer increases fuel mileage by 8 to 12 over driving in the winter months Temperature also affects the tires inflation pressure Tire inflation tends to fall when the temperature drops Running tires low on air pressure in hot weather is more of a safety issue than a fuel econ
12. e 23 of 35 highways with average loads somewhat less than 80 000 Ibs these recommendations will optimize fuel economy for fuel conscious fleets Selection of the appropriate drivetrain components is critical to achieving drivability and mpg goals Direct drive transmissions can yield a 2 advantage in mpg in a linehaul application from lower Gear mesh losses Spin oil churn losses For More Information Go to www powerspec cummins com to view some application specific gearing recommendations Vehicle Operating Techniques Excessive speed decreases fuel economy In addition excessive idling operating the vehicle in the wrong gear and accelerating and decelerating rapidly all consume extra fuel It has been proven that poor driving techniques can account for up to a 30 reduction in fuel economy Driver behavior can account for up to 30 variation in fuel economy p b gt G Least Most gt Efficient Efficient Drivers Drivers Fuel Economy MPG Secrets of Better Fuel Economy Page 24 of 35 Efficient Driving Behavior The following is a short list of behaviors exhibited by those drivers that consistently obtain good fuel economy Simple behaviors like coasting to a stop instead of staying on the accelerator until the last minute and then braking hard add up to significant fuel savings after thousands of miles High average vehicle speeds with minimum time spent at maximum veh
13. etween a good mpg driver 0 to 30 and a poor mpg driver in each fleet Recommend using LBSC One gear down you decrease mpg by approx 3 due to gear mesh effect The engine cruising rpm is approx 400 rpm higher which decreases mpg by approx 4 Higher density air wind cross and head more idle time blended fuel lower BTU snow more driveline drag etc 8 15 decreased MPG compared to Summer Fan HP increases with rpm X HP cubed When cooling fans are running they use between 1 5 and 3 5 gallons of fuel per hour Increasing fan run distance from 30 to 50 will decrease MPG by between 3 to 5 1 mpg imph gt 55 mph This is a rule of thumb Page 32 of 35 Appendix B General Information on Fuel Consumption The Fuel Consumption General Information section of the Troubleshooting and Repair Manual Signature ISX QSX15 Engines Bulletin 3666239 and Troubleshooting Excessive Fuel Consumption Bulletin Number 3666094 should be referenced prior to any troubleshooting being performed on a customer s engine The cause of excessive fuel consumption is hard to diagnose and correct because of the potential number of factors involved Actual fuel consumption problems can be caused by any of the following factors Engine factors Vehicle factors and specifications Environmental factors Driver technique and operating practices Fuel system factors Low power drivability problems Before troubleshooting it is impo
14. fuel economy Used lug drive tires can get up to 0 4 mpg better than new lug tires Ribbed tires on the drive axles provide 2 4 better fuel economy than lugged tires Every 10 psi that a truck s tires are underinflated reduces fuel economy by 1 The break in period for tires is between 35 000 and 50 000 miles Tires make biggest difference in mpg below around 50 mph aerodynamics is the most important factor over around 50 mph The most efficient drivers get about 30 better fuel economy than the least efficient drivers Idle time is costly Every hour of idle time in a long haul operation can decrease fuel efficiency by 1 Secrets of Better Fuel Economy Page 4 of 35 Vehicle Power Requirements In the simplest of terms you burn fuel to make horsepower and you use horsepower to overcome all of the forces that are trying to retard or hold back the truck So a truck that rolls down the road with minimum drag will use less horsepower and consume less fuel The power required to maintain a given road speed depends on the sum of the following forces Aerodynamic Drag Grade Resistance Tire Rolling Resistance Engine Accessory Drivetrain losses This section reviews these items in detail to demonstrate the impact of each on fuel savings Aerodynamic Drag Aerodynamic drag is the result of forces pressure imbalances acting on a vehicle as it passes through the air The magnitude of the forces acting on a vehicle depends on
15. icle speed High percent trip distance in top gear 90 recommended High percent distance in cruise control Minimum percent Idle PTO operation Minimum service brake activity e Number of Sudden Decelerations e Service Brake Actuation s 1000 mi Rock Solid Rule The most efficient drivers get about 30 better fuel economy than the least efficient drivers Secrets of Better Fuel Economy Page 25 of 35 Pre Trip Inspection Conduct daily vehicle pre trip inspections Such inspections should include checks of the following Engine lube oil level Tire inflation pressures Service brake adjustment Air system leaks Coupling device Inspections reduce the potential for unscheduled downtime or vehicle related accidents and improve fuel economy Road Surface Even road surface has a documented effect on fuel economy Using new concrete as the standard baseline worn or polished concrete is even better All other road surfaces are worse some substantially Table 7 Tire Rolling Resistance Pavement Type and Condition versus Relative Rolling Resistance Relative Rolling Road Surface Resistance Concrete polished best mpg 12 new baseline Asphalt with finish coat 1 medium coarse finish 4 coarse aggregate 8 Chip and Seal Blacktop worst mpg 33 Road roughness can increase rolling resistance up to 20 due to energy dissipation in the tires and suspension 10 loss of mpg Secrets of Better Fuel Economy
16. ills Letting the engine RPM s approach peak torque before downshifting will get you over the hill faster and with less fuel consumed If you spec too much horsepower you encourage drivers to accelerate rapidly and drive faster but spec ing too little horsepower reduces gradeability and creates driver dissatisfaction Secrets of Better Fuel Economy Page 12 of 35 Lubricants While the efficiency of drivetrain components is largely fixed by design gross efficiency losses can be minimized through proper selection of lubricants Synthetic base lubricants are manufactured in the laboratory to exhibit superior high temperature stability and low temperature fluidity Since these fluids are created to exhibit less thickening at low temperatures pumping losses are reduced and substantial reductions in spin losses can be realized at low operating temperatures Test results indicate no significant difference in engine efficiency between synthetic and mineral base lube oils at normal operating temperatures Since the synthetics are more expensive and in an engine crankcase are subject to the same contaminants as mineral based oils they may not be cost effective All oils thicken at low temperature causing increased fuel consumption The synthetic oil is less affected by temperature This makes synthetic oils more fuel efficient at lower ambient temperatures Effects of Lubricant Temperature and Performance 2 N D
17. n Pressure Proper inflation pressures critically affect tire performance Underinflation can negatively affect tire performance and durability Specifically it Reduces fuel economy Increases tire wear rates Creates irregular tread wear Reduces casing durability Every 10 psi of underinflation represents approximately 1 penalty in fuel economy The effect of running all tires slightly underinflated blue line on the chart is significant But all tires do not contribute equally Notice that the trailer tires green line on the chart have a larger effect on fuel economy than either steer or drive tires The tires most likely to be ignored poorly maintained or underinflated are in the trailer position where old tires with irregular wear are often placed to run out any remaining tread Radial Truck Tire Inflation versus Percent Change in MPG s EE ide Front Axle mmmmmmn Drive Axles _ Trailer Axels Front Drive and Trailer Axles Difference in MPG HKNHKGONNSOGOA NNOWMPN oacaqaoagaoaoocdaqacaqocaoucuacouea 60 65 70 75 80 85 90 95 100 105 no 115 120 GCW 78 780 Ibs Tire Inflation psi V 55 MPH 9 92 Goodyear radial truck tire service manual Secrets of Better Fuel Economy Page 22 of 35 Powertrain Guidelines Every engine has a sweet spot where it delivers its best fuel economy To optimize fuel economy the engine should run at this speed during normal highway cruising When spec
18. nges MPG A 7 32 tread wear represents 10 reduction in rolling resistance 5 better mpg compared to a new tire Rib tires at all wheel positions will provide om greatest fuel efficiency Tread pattern is important because lugs have E TI re N 2 4 16 18 24 26 28 deeper tread more rolling resistance than ribs If Depth 32nd s we take a new ribbed tire as the standard a new Tully Type lugged tire is less fuel efficient by about 6 A worn Rib Drive Lug tire is about 7 more fuel efficient than a new tire Casing Design As we mentioned earlier tires that run hotter consume more fuel A majority of this heat is generated by sidewall flex New and improved casing designs minimize sidewall flex and reduce running temperatures It pays dividends to run tires with good casing design Secrets of Better Fuel Economy Page 16 of 35 Wide Based Tires Fleets can improve rolling resistance even more by using wide based tires on drive and trailer axles Closed track tire testing has shown as much as 4 MPG improvement over conventional dual rib tires on drive and trailer axle positions Rock Solid Rule Every 10 psi of underinflation represents approximately 1 penalty in fuel economy Secrets of Better Fuel Economy Page 17 of 35 Engine Operation and Maintenance Getting the most out of the engine means running it at the right rom To truly optimize economy you need to optimize several other engine ope
19. omy problem And heat is the tire s worst enemy For safety and economy check inflation pressures frequently with an accurate tire gauge When seasons change and temperatures fluctuate increase the frequency of inflation pressure checks Wind Headwinds and crosswinds can significantly increase aerodynamic drag and reduce fuel efficiency For every 10 mph of headwind or crosswind mpg is reduced by nearly 13 You cannot cheat increasing wind resistance Rain and Snow Precipitation such as rain or snow increases rolling resistance because the tires must push their way through the water slush or snow on the pavement Also water is a more effective coolant than air so the tires transmission lubricant and axle lubricant operate at cooler less efficient temperatures Rolling resistance and drivetrain friction in light rain increase fuel consumption by 0 2 to 0 3 mpg per SAE testing Fuel Blends While blended fuels provide better startability and protection against fuel gelling than standard 2 diesel fuel efficiency decreases Summer fuel improves mileage up to 3 more than winter fuel Secrets of Better Fuel Economy Page 30 of 35 Biodiesel Fuels Some biodiesel blends can also affect MPG B20 fuel has been shown to reduce MPG by 1 where as a B5 blend shows a negligible difference in fuel economy ULSD Ultra Low Sulfur Diesel Fuels ULSD fuel can show a 1 decrease in fuel economy compared to 500 ppm fuel
20. or to vehicle power requirements Tire rolling resistance is influenced by multiple factors Vehicle speed Load GCW Inflation Pressures Tire construction tread type depth Ambient temperature Road Surface Vehicle tire and axle alignment Load Direction of Travel Tire Rolling Resistance Vehicle Speed Tires flex more at higher speeds This leads to more friction higher tire temperatures and reduced fuel economy Remember the rule that fuel economy goes down about 0 1 mpg for every mile per hour over 55 That rule takes tire rolling resistance and aerodynamic drag into consideration Secrets of Better Fuel Economy Page 15 of 35 Weight Impact Increased weight causes increased flexing of the tires Reducing the weight of components on the truck can result in either better fuel economy or increased payload for the same amount of fuel consumed Of course tires should always be rated for the loads carried and properly inflated Table 3 The Role of Weight on Rolling Resistance Rolling Resistance Power Requirement h 80 000 lbs GCW 87 hp 65 000 lbs GCW 71 hp 16 hp difference MPG advantage assuming 250 hp road load 6 better mpg w lower GCW Tread Depth and Pattern According to Bridgestone the tire tread accounts for 60 70 of the tires rolling resistance Not only do the tires differ in rolling resistance when new but as 80 the tread wears the rolling resistance of the tire cha
21. rating characteristics Engine Operating Temperature Coolant and Lube Oil Low coolant temperatures indicate an engine that is too cold for efficient combustion Fuel liquefies on the cold cylinder walls and fails to burn Of course excess heat causes engine failure Lube oil below the ideal temperature is more viscous and harder to pump Oil above the ideal temperature is too thin to lubricate properly Either way the engine suffers Coolant and lube oil operating temperatures can contribute greatly to fuel efficiency Typical cooling system operating temperatures are above 180 F A 0 4 fuel economy loss is associated with every 30 decrease in temperature Lube system operating temperatures run above 225 F and a 1 fuel economy loss is associated with every 30 decrease in lube temperature Intake and Exhaust Restriction An engine that is starved for air intake restriction or unable to expel exhaust exhaust restriction will lack power and waste fuel The extra fuel burns inefficiently at best because it takes air to completely oxidize the fuel and extract all of the power that it contains Fuel Line Restriction In addition to the air restrictions listed above excessive fuel line restriction will also reduce MPG Be extra cautious of any device that attaches to the fuel lines claiming to improve MPG At best Cummins has tested these devices and found no MPG improvement Secrets of Better Fuel Economy Page 18 of 35
22. rtant to determine the exact complaint Is the complaint based on whether the problem is real or perceived or does it not meet the driver s expectations The Fuel Consumption Customer Complaint Form provides a valuable list of questions to assist the service technician in determining the cause of the problem Complete the form before troubleshooting the complaint The following are some of the factors to consider when troubleshooting fuel consumption complaints Result of a Low Power Drivability Problem An operator will change driving style to compensate for a low power drivability problem Some of the things the driver will likely do include shifting to a higher engine rpm or running on the droop curve in a lower gear instead of upshifting to drive at part throttle conditions These changes in driving style will increase the amount of fuel used Driver Technique and Operating Practices As a general rule a 1 mph increase in road speed equals a 0 1 mpg increase in fuel consumption This means that increasing road speed from 50 to 60 mph will result in a loss of 1 mpg Secrets of Better Fuel Economy Page 33 of 35 Environmental and Seasonal Weather Changes Generally there can be as much as 1 to 1 5 mpg difference in fuel consumption depending on the season and the weather conditions Excessive Idling Time Idling the engine can use from 0 5 to 1 5 gallons per hour depending on the engine idle speed Truck Route and Terrain East we
23. ssesseessessssssseseeeneeseeees 23 Vehicle Operating TeCHNiques scscssssssssssssssscsssssssssssssssscscsesessesesesasscasessesesavavasasensess 24 Efficient Driving Behavior Vvs ee 25 Pre Trip Inspection eek e bine ba nals esecenenia teat nae an nenene 26 Road SE HST 26 Shifting TEN eee 27 EFC A CIN aie e E E EE 29 Weather and Seasonal C Onions dcscscccacedsetacreclgucscedaraaasiocuecistaaiciaatadeneeeatuedieaees 30 Ambient T NU nts sniadeatoantvauhinciddctsiuaniadendatesiaatirs 30 MM 30 Rainand SNOW EE ele eee 30 01150 EE EE diana sepinecestiona stnesotanpbsiiebenedsubiusue 30 Appendix A Customer MPG Effect Worksheet ccccssssssssssssessssssssssseenesssssesesesesersees 32 Appendix B General Information on Fuel Consumption ccccccccessessstsssessssseeeeeess 33 Secrets of Better Fuel Economy Page 3 of 35 Introduction Understanding Fuel Economy The importance of fuel economy to the successful operation of a trucking company cannot be understated Fuel is one of the largest variable costs in a trucking venture and while no trucking operation can control the cost of fuel it has at least some control over the amount or rate of consumption Rock Solid Rules Every 2 reduction in aerodynamic drag results in approximately 1 improvement in fuel economy Above 55 mph each 1 mph increase in vehicle speed decreases fuel economy by 0 1 mpg Worn tires provide better fuel economy than new tires up to 7 better
24. st routes experience almost continual crosswinds and head winds Less fuel can be used on north south routes where parts of the trip are not only warmer but see less wind resistance Vehicle Aerodynamics The largest single power requirement for a truck is the power needed to overcome air resistance As a general rule each 10 percent reduction in air resistance results in a 5 percent increase in mpg Rolling Resistance Rolling resistance is the second largest consumer of power ona truck The type of tire and tread design have a sizeable effect on fuel economy and performance Fuel efficient tires have demonstrated gains as high as 0 5 mpg Secrets of Better Fuel Economy Page 34 of 35 Appendix C Effects of First Fill First Fill Effects OFAN WK TDN 20000 40000 60000 80000 100000 120000 140000 Miles Driven Secrets of Better Fuel Economy Page 35 of 35
25. t the ideal rom Every engine is a bit different so the ideal rom for one engine isn t the same for another To find the gearing recommendations for Cummins engines use Cummins PowerSpec at www powerspec cummins com to calculate the engine rpm for a given cruising speed based on transmission gearing axle gearing and tire size This makes finding the ideal gearing almost effortless The startability value represents the maximum grade on which the vehicle can be put into motion without using the accelerator when loaded to the specified vehicle weight using the lowest transmission gear ratio While the transmission top gear ratio determines cruise rpm startability is determined by the transmission s first or low gear ratio This may not seem important for an OTR tractor where only a few interstates have grades in excess of 7 but pulling away from a loading dock can test the startability of a tractor under adverse circumstances The power required to move the vehicle increases depending on the vehicle weight and the steepness of the grade Gradeability is the vehicle s ability to climb a grade at a given speed For example a truck with a gradeability of 4 at 65 mph can maintain 65 mph on a 4 grade Any steeper grade will cause a reduction in vehicle speed while climbing the hill Gradeability at peak torque comes into play when ascending the hills Some driver s first response is to downshift into lower gears as they start to ascend the h
26. tance also reduces power output from 145 hp to 113 hp a reduction of 22 Level Road Power Requirements 0 AERO 113 HP NN TIRE 87 HP 0 MISC 32 HP POWER REQUIREMENTS 65 MPH 230 HP 500 ENGINE RPM 1450 T 65 MPH I 400 GCW 80000 Ib Oo 300 2 200 z O ou o 0 10 20 30 40 50 60 70 80 90 ROAD SPEED MPH Notice that these aerodynamic treatments are more effective at higher speeds as represented by the increased vertical depth of the red graph above Also notice that the power required to overcome things like tire rolling resistance are not affected by the aerodynamic aids Secrets of Better Fuel Economy Page 7 of 35 The following graph shows how the impact of aerodynamic treatments depends on speed For trucks in pickup and delivery operations in urban areas the cost and maintenance of aerodynamic treatments may outweigh the benefits However for an over the road OTR tractor and trailer the fuel savings from aerodynamic treatments may quickly offset the higher initial purchase price of the equipment Aerodynamic Power Requirements 280 pr e No Air Aids Full Air Aids Power Requirement Bhp N ros 50 55 60 65 70 75 80 85 90 Vehicle Speed MPH At approximately 0 3 Ib BhpHr fuel consumption a reduction of 35 Bhp required to cruise at 65 mph results in a savings of about 10 5 Ibs of fuel every hour 0 3 x 35 10
27. tor trailer air gap increases aerodynamic drag by approximately 2 If axle weights allow slide the fifth wheel forward to minimize the gap and reduce wind resistance Rock Solid Rule Every 2 reduction in aerodynamic drag results in approximately 1 improvement in fuel economy Secrets of Better Fuel Economy Page 10 of 35 Trailer Body Aerodynamics Drag characteristics of miscellaneous trailer configurations and body styles can vary and therefore will impact fuel economy A straight side van trailer with rounded corners at the front offers the least resistance Table 2 Common Trailer Bodies Exhibiting Higher Drag Increase in Aerodynamic Drag Single Trailers Square corner vertical rib van 5 10 2 5 to 5 mpg Flatbed with irregularly shaped loads 10 30 5 to 15 mpg Cattle haulers 10 30 Car haulers 10 30 Double Triple Trailers Doubles 10 Triples 15 Engine Accessory Drivetrain Losses Although largely fixed engine accessory and drivetrain losses can significantly contribute to total vehicle power requirements Engine accessories consist of Cooling fan Freon compressor Air compressor Alternator Power steering Drivetrain consists of Oil Windage Churning Frictional losses Secrets of Better Fuel Economy Page 11 of 35 Gearing The rpm level where the engine cruises can provide critical fine tuning of fuel economy To do this you can spec the gearing so that the engine runs a
28. y Fuel economy is assured when loads are light and the driver still gets the engine speed and power needed when the loads are heavy LBSC can reduce the variability between your least efficient and most efficient drivers Secrets of Better Fuel Economy Page 27 of 35 As you ve seen the lower gears are good for power but not for economy Gear Down Protection maximizes the percentage of distance in top gear which should be greater than 90 When the driver downshifts the gear down protection cuts back on the top speed encouraging the driver to stay in top gear Gear down protection also senses engine load to make sure that it doesn t limit the engine speed when the downshift is truly justified due to a heavy load You can calculate and select the settings or you can just let the experts calculate the optimum settings for you Cruise Operation Cruise control can be a great equalizer While some of the very best drivers may still be able to obtain better fuel economy without using the cruise control cruise control in general can make every driver better than average Anticipating Change The key to effective cruise operation is anticipating changes that may occur while driving on the open road Maintaining a high field of vision and establishing proper following distances is a good start Drivers should also do the following Anticipate changes in traffic and road conditions Avoid abrupt stops or rapid changes in vehicle speed
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