www.ext.vt.edu

Produced by Communications and Marketing, College of Agriculture and Life Sciences, 

Virginia Polytechnic Institute and State University, 2010

Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, 

age, disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. 

Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, 

and the U.S. Department of Agriculture cooperating. Alan L. Grant, Dean, College of Agriculture and Life Sciences, and Interim 

Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Wondi Mersie, Interim Administrator, 1890 Extension 

Program, Virginia State, Petersburg.

PUBLICATION 442-073

General relationships capable of predicting tractor diesel fuel consumption are very useful for budget and 

management purposes but may not have the ability to 

compare fuel consumption for several potential engine 

configurations, such as turbocharging and air densification components. The objective of this factsheet is to 

examine several methods that use field measurements 

and Nebraska Tractor Test Laboratory results to estimate fuel consumption. Using these equations, farmers 

can estimate and compare the fuel savings for different 

operating and loading conditions.

Introduction

According to Siemens and Bowers (1999), “Depending 

on the type of fuel and the amount of time a tractor or 

machine is used, fuel and lubricant costs will usually 

represent at least 16 percent to over 45 percent of the 

total machine costs. ...” Thus, fuel consumption plays 

a significant role in the selection and management of 

tractors and equipment. Currently, most budget models use a simplified method for estimating diesel fuel 

consumption. Better estimates representing actual field 

operations are needed to compare machinery management strategies.

The worth of a tractor is measured by the amount of 

work that can be accomplished and the cost associated 

with completing the task. Drawbar power is defined by 

pull (or draft) and travel speed. An ideal tractor would 

convert all fuel energy into useful work at the drawbar. 

However, due to power losses, not all fuel energy is 

converted into useful work.

Efficient operation of farm tractors includes (1) maximizing the fuel efficiency of the engine and the mechanical efficiency of the drivetrain, (2) maximizing tractive 

advantage of the traction devices, and (3) selecting an 

optimum travel speed for a given tractor-implement 

system. This factsheet focuses on methods to estimate 

and improve fuel efficiency of a diesel power unit.

The Nebraska Tractor Test Laboratory (NTTL) has a 

long history of testing tractors and disseminating power 

and fuel consumption data. The NTTL is the official testing station for agricultural tractors in the United States. 

Tractors manufactured in the United States and other 

countries are tested, and NTTL publishes the test results. 

During standardized tests, the power is calculated and 

the corresponding fuel consumption is measured. The 

power at the power takeoff (PTO) is calculated from the 

torque and speed at the PTO. Drawbar power is calculated from the drawbar pull and the forward speed of the 

tractor. For more details and for a sample test report, see 

Using Tractor Test Data for Selecting Farm Tractors, 

Virginia Cooperative Extension publication 442-072. 

Terminology

Tractor manufacturers specify power output at several tractor locations, such as power takeoff, drawbar, 

hydraulic outlets, and electrical outlets. For each tractor 

model, the rated power output is measured at the rated 

engine speed. Typically, this power is measured at the 

PTO, and in this factsheet, it is referred to as “rated 

PTO power.” For most modern tractors, the rated power 

will not be the maximum available power. Most modern 

engines often produce more power because they can be 

operated at speeds other than rated speeds. 

Fuel consumption is measured by the amount of fuel 

used during a specific time period. The most common 

measure of the energy efficiency of a tractor is referred 

to here as “specific volumetric fuel consumption” 

Predicting Tractor Diesel Fuel Consumption

Robert “Bobby” Grisso, Extension Engineer, Biological Systems Engineering, Virginia Tech

John V. Perumpral, Professor Emeritus, Biological Systems Engineering, Virginia Tech

David Vaughan, Professor, Biological Systems Engineering, Virginia Tech

Gary T. Roberson, Associate Professor and Extension Specialist, North Carolina State University 

Robert Pitman, Superintendent, Eastern Virginia Agriculture Research and Extension Center, Virginia Tech
2

(SVFC), which is given in units of gallons per horsepower-hour (gal/hp-h). Specific volumetric fuel consumption is generally not affected by engine size, and 

it is used to compare the energy efficiencies of tractors 

with different size engines and under different operating conditions. SVFC for diesel engines typically 

ranges from 0.0476 to 0.1110 gal/hp-h. 

For ease of computation, the reciprocal of SVFC is 

often used and is referred to here as “specific volumetric fuel efficiency” (SVFE) with units of horsepowerhours per gallon (hp-h/gal), with corresponding ranges 

from 12 to 21 hp-h/gal. 

The NTTL reports the SVFE for several drawbar load 

tests, rated PTO speed, and varying PTO power tests. 

Figure 1 shows sample data from an NTTL report. The 

SVFE for this test is shown under the columns labeled 

with units of hp-h/gal (kW-h/L). For example, at rated 

engine speed, the tractor shown in figure 1 developed 

115.96 PTO horsepower with an SVFE of 17 hp-h/gal.

The data measured in NTTL Report 1725 (shown in figure 1) is used to demonstrate the computation for equation (4). For the drawbar performance at “75% of Pull at 

Maximum Power,” the engine speed was 2,190 rpm, and 

the SVFE was 12.80 hp-h/gal. The corresponding test with 

a reduced throttle setting had an engine speed of 1,665 rpm 

and an SVFE of 14.63 hp-h/gal. The SVFC was calculated 

as 0.0781 gal/hp-h for full throttle and 0.0684 gal/hp-h for 

the reduced throttle test. The decrease in SVFC was 12.4 

percent, while the engine speed was reduced by 24 percent. Similarly, the “50% of Pull at Maximum Power” tests 

resulted in a 24 percent reduction in engine speed and a 

15.8 percent decrease in SVFC.

Tractor Fuel Efficiency 

Improvements 

Newer tractors are generally more efficient than models 

produced 20 years ago. Improvements in fuel efficiency 

during the last 20 years prove this point. Figure 2 shows 

the average and maximum specific fuel consumption 

of tractors tested from 1980 to 2000. Models tested in 

2000 averaged 16.5 hp-h/gal, compared to an average 

of 14.5 hp-h/gal for models tested in 1980. The fuel 

savings of 10 to 15 percent became possible because 

of improved engine/transmission design and improved 

ability to match tractors and implements for given field 

conditions. Today’s tractors have more electronic controls for more efficient delivery of power to the PTO, 

drawbar (for pulling), and hydraulic lifts and controls.

The reduction in fuel efficiency seen during years 

1991, 1998, and 2004 (figure 2) is attributed to the new 

emission requirements that went into effect for offroad vehicles. Even though Environmental Protection 

Agency (EPA) regulations initially challenged engine 

designers, fuel efficiency has improved significantly 

since then. All tractors are not equal in fuel consumption. The maximum value line in figure 2 represents the 

fuel efficiency for the most fuel-efficient tractor for that 

year. The fuel consumption data is an important consideration during the selection and purchase of a tractor.

Figure 2. The average and maximum fuel efficiency 

(hp-hr/gal) for almost 30 years. This chart shows results 

averaged from annual NTTL reports (typically 10-30 

tractors per year).

Fuel Consumption Estimates

ASABE Standards (2006, 2009) are widely used for 

estimating fuel consumption for budget preparations. 

The most widely used relationship for estimating fuel 

consumption in gallons per hour (gal/h) is

QAVG = a′ ∙ PPTO (1)

where

QAVG = average diesel consumption (gal/h),

PPTO = rated PTO power (hp),

a′ = 0.044 gal/hp-h.

Bowers (2001, e-mail correspondence) stated that 

equation (1) was developed based on PTO power test 

results from the Nebraska Tractor Test reports during 

the mid-1970s. The fuel consumption (gal/h) over the 

varying PTO power tests (approximately 100 percent, 

85 percent, 65 percent, 45 percent, 20 percent, and 0 

percent of rated PTO power) were averaged, then the 

average was divided by the rated PTO power. For this 
3

Power Take-Off Performance

Power 

HP

(kW)

Crankshaft 

speed rpm

Gal/br

(l/h)

lb/hp.hr

(kg/

kW.h)

Hp.hr/

gal

(kW.h/l)

Mean Atmospheric 

Conditions

Maximum Power and Fuel Consumption

Rated Engine Speed (PTO speed — 1006 rpm)

115.96

(86.47)

2100 6.82

(25.82)

0.413

(0.251)

17.00

(3.35)

Maximum Power (2 hours)

117.27

(87.45)

1801 6.51

(24.66)

0.390

(0.237)

18.00

(3.55)

Varying Power and Fuel Consumption

115.96

(86.47)

2100 6.82

(25.82)

0.413

(0.251)

17.00

(3.35) Air Temperature 

75°F 

(24°C) 

Relative humidity 

47% 

Barometer 

28.86” Hg

(97.73 kPa)

102.08

(76.12)

2170 6.33

(23.95)

0.435

(0.265)

16.13

(3.18)

77.46

(57.76)

2202 5.26

(19.91)

0.476

(0.290)

14.73

(2.90)

52.03

(38.81)

2233 4.28

(16.18)

0.576

(0.351)

12.17

(2.40)

26.27

(19.59)

2257 3.12

(11.81)

0.834

(0.507)

8.42

(1.66)

1.03

(0.77)

2267 2.05

(7.77)

13.915

(8.464)

0.50

(0.01)

Maximum Torque 407 lb/ft (552 Nm) at 1247 rpm

Maximum Torque Rise 40.3%

Torque rise at 1699 engine rpm 24%

Drawbar Performance Unballasted — Front Drive Engaged

Fuel Consumption Characteristics

Power Hp

(kW)

Drawbar 

pull ls

(kN)

Speed 

mph

(km/h)

Crankshaft 

speed rpm Slip %

Fuel Consumption Temp. °F (°C) Barom. 

inch Hg

(kPa)

lb/hp.hr

(kg/kW.h)

Hp.hr/gal

(kW.h/l)

cooling 

med

Air dry 

bulb

Maximum Power 11th Gear

96.26

(71.78)

6631

(29.49)

5.44

(8.76)

2099 2.24 0.490

(0.298)

14.33

(2.82)

190

(88)

76

(24)

28.87

(97.77)

75% of Pull at Maximum Power 11th Gear

75.72

(56.47)

4967

(22.09)

5.72

(9.20)

2190 1.54 0.548

(0.333)

12.80

(2.52) 

187

(86)

77

(26)

29.02

(98.27)

50% of Pull at Maximum Power 11th Gear

51.48

(38.39)

3313

(14.73)

5.83

(9.38)

2221 1.26 0.651

(0.396)

10.78

(2.12)

184

(84)

78

(26)

28.98

(98.14)

75% of Pull at Reduced Engine Speed 13th

75.86

(56.57)

4950

(22.02)

5.75

(9.25)

1665 1.75 0.480

(0.292)

14.63

(2.88)

187

(86)

77

(25)

29.00

(98.21)

50% of Pull at Reduced Engine Speed 13th

51.60

(38.48)

3310

(14.72)

5.85

(9.41)

1685 1.26 0.548

(0.333)

12.80

(2.52)

178

(81)

79

(26)

28.96

(98.07)

Figure 1. Example of a Nebraska Tractor Test Laboratory (NTTL) report. The sections show: top, the PTO performance 

tests; center, the varying power tests; and bottom, the drawbar performance test results. This is taken from the report of 

Nebraska OECD Tractor Test 1725 – Summary 225 for John Deere 7610 PowerShift.
4

reason, the annual fuel consumption estimates using this 

method give fuel consumption based on the assumption 

that the tractor is operated under the same load pattern 

for equal time. Due to this assumption, this method 

underestimates fuel consumption.

Field Measurement 

of Fuel Consumption

Farmers may consider numerous ways to estimate and 

reduce fuel consumption. The first step is to determine 

how much fuel is being used for a particular field operation and compare it to average usage. This measurement can be completed by filling the fuel tank of the 

tractor before and after a field operation, noting the 

number of acres covered. The number of gallons used, 

divided by the number of acres covered, gives the fuel 

consumption in gallons per acre (gal/ac). The resulting 

estimate of fuel consumption can be compared to the 

values listed in table 11

. If measured fuel consumption 

is higher than the estimated average, the following tips 

should be considered to reduce fuel consumption:

• Eliminate one or more tillage/field operations. 

• Substitute one type of tillage operation for another 

(e.g., chisel for plow).

• Combine tillage and other operations into one pass 

over the field.

• Optimize tractor performance (proper amount and 

distribution of ballast, tire inflation, etc.). 

• Use “gear-up, throttle-down” (GUTD) practices. 

• Properly match tractor and implement sizes.

• Optimize field efficiency with controlled traffic and 

navigation aids.

• Ensure sufficient machine maintenance.

Better Fuel Consumption 

Estimates

Two methods (general and specific) have been developed for estimating fuel consumption from Nebraska 

Tractor Test results. Both methods are based on tractor 

test results using the relationships between engine load 

and engine speed (rpm). The “general” method is based 

on the average results from more than 500 tractors. The 

“specific” method used the mathematical relationship 

found in the general model but is derived from the test 

results of a specific tractor.

Fuel consumption is estimated from reduced engine 

load and from full-throttle data (along the governor 

response power curve). ASABE Standards’ (2009) general fuel consumption equations for compression ignition engines were developed as follows:

QF = (0.0434X + 0.019) ∙ PPTO (2)

where

QF = diesel fuel consumption at partial load and full 

throttle (gal/h),

X = fraction of equivalent PTO power available (decimal).

X = P ⁄ PRATED 

where 

P = equivalent PTO power required by current operation (hp),

PPTO = rated PTO power available (hp).

QR = QF · [1 − (N − 1) ∙ (0.45X − 0.877)] (3)

where

QR = diesel fuel consumption at partial load and reduced 

throttle (gal/h),

N = ratio of reduced- and full-throttle engine speeds at 

operating load (decimal).

N = RPMPT / RPMFT 

where 

RPMPT = engine speed at partial throttle at reduced 

engine speed (rpm),

RPMFT = full-throttle engine speed (rpm).

These general equations are useful for predicting fuel 

consumption for diesel engines during full and partial 

loads and under conditions when engine speeds are 

reduced from full throttle.

Fuel Consumption Estimates 

for Specific Tractor Models

The second method for estimating fuel consumption 

was developed from the general model (equations (2) 

and (3)) and was used to derive the coefficients for specific tractor models. The method uses the NTTL test 

results, and the defining locations of the fuel consumption parameters are shown in figure 3. The equation for 

a specific tractor is defined as:

1

Table 1 reports fuel consumption values for many field operations summarized from various states. Although data is 

not included from every state and is dated, the values may be useful as guidelines to determine whether fuel usage for a 

particular operation is reasonable.
5

Table 1. Diesel fuel consumption for field operations.

Operation

Farm energy audita

Range (gal/ac) Average from 

other states Average High Low b

Primary tillage

Moldboard plow 1.81 3.50 0.90 1.87

Chisel disk 1.36 3.50 0.80 1.09

Offset disk 1.11 1.20 0.90 0.97

Subsoiler 1.54 2.30 1.10 1.56

Secondary tillage

Disk 0.93 3.30 0.30 0.65

Field cultivator 0.78 1.80 0.30 0.68

Spring tooth harrow (drag) 0.73 1.80 0.20 0.48

Fertilizer and chemical application

Pesticide spraying 0.33 2.90 0.10 0.13

Chemical incorporation 0.80 1.10 0.50 –

Spreading fertilizer 0.30 0.50 0.10 0.19

Knife in fertilizer 0.58 1.30 0.20 1.05

Planting

Row crop planter 0.51 1.00 0.20 0.54

Grain drill 0.56 2.31 0.10 0.33

Potato planter 0.95 1.90 0.90 0.95

Broadcast seeder 0.28 1.12 0.10 0.15

No-till planter 0.68 – – 0.43

Cultivation

Cultivator 0.39 1.90 0.10 0.42

Rotary hoe 0.23 0.70 0.10 0.21

Forage harvesting

Mower/conditioner 0.72 1.80 0.30 0.66

Rake 0.46 1.26 0.20 0.24

Baler 0.65 2.90 0.10 0.69

Large round baler 0.80 – – –

Forage harvester or green chop 1.57 2.00 0.20 1.87

Corn silage harvester 3.14 6.70 1.70 2.69

Grain and row crop harvest

Small grain or bean combine 1.23 1.80 0.70 1.01

Corn combine 1.51 2.20 0.70 1.37

Corn picker 1.84 3.00 1.20 1.10

Pull and window 0.52 1.10 0.30 0.34

Beet harvester 1.37 1.90 0.90 1.91

Topping beets 0.83 1.20 0.40 1.47

Potato harvester 2.69 – – 1.73

PTO operated (gal/hr)

Forage blower 2.19 6.20 0.90 –

Irrigation 3.41 4.40 1.10 –

Grinding 3.84 6.90 2.20 – a

Helsel, Z., and T. Oguntunde. 1985. Fuel requirements for field operations with energy saving tips. In Farm 

Energy Use: Standards, Worksheets, Conservation, ed. C. Myers. East Lansing: Michigan State University. b

Iowa, Pennsylvania, Nebraska, Missouri, New York, Oklahoma, North Dakota, and Ontario, Canada
6

Q = (aX + b) ∙ [1 − (N − 1) ∙ (cX − d)] ∙ PPTO (4)

where

a, b, c, and d coefficients are defined in appendix A,

Q = diesel fuel consumption (gal/h),

X = ratio of equivalent PTO power to rated PTO power 

(decimal),

N = ratio of reduced- and full-throttle engine speeds at 

operating load (decimal),

PPTO = rated PTO power (hp).

Figure 3. Engine map with the tractor test information and 

notations described. 

Coefficients (a, b, c, and d) were computed for specific 

tractors tested from 1986 through 2008. More than 770 

tractors with complete drawbar tests (both 50 percent 

and 75 percent pull tests) were considered. Calculating 

the coefficients for each individual tractor showed significant improvement in accuracy. These coefficients 

may be computed for a specific tractor (of your choice) 

as shown in appendix A or by downloading and using 

an Excel spreadsheet that is available at: http://filebox.

vt.edu/users/rgrisso/Tractor.htm. For tractors already 

available, the coefficients have been calculated and can 

be downloaded at the same URL.

Fuel Consumption Comparison

Estimated fuel consumption for the John Deere 7610 

(JD7610) is compared against measured fuel consumption during the Nebraska tractor test in table 2. 

The agreement between estimated fuel consumption – 

using equation (4) – and measured fuel consumption 

was good. On the other hand, estimates using the general model were found to be slightly higher. Estimates 

from the traditional method were consistently lower 

than the actual fuel consumption for full-load tests. The 

best estimates were from the specific tractor model; the 

second-best estimates were from the general method. 

Both showed the impact of GUTD practices.

Specific Model Application

The NTTL report can be a very useful resource when 

deriving the coefficients for equation (4). As shown 

in the example in appendix A, the coefficients can be 

derived directly from the NTTL reports. To use the specific model to predict fuel consumption for a given field 

operation, ensure that the current engine and the engine 

reported in the NTTL report are adjusted in the same 

manner. The high-idle (full-throttle, no-load) engine 

speed shown in the “Varying Power and Fuel Consumption” section of the NTTL report must be compared with 

the current engine setting. For example, the high-idle 

engine speed shown in the NTTL report example (figure 1) is 2,267 rpm. The user’s high-idle engine speed 

(RPMHI) can be determined by observing the engine 

speed at full throttle and no load. If the high-idle engine 

speed is significantly different from the NTTL reported 

speed, errors using this approach can be significant.

To determine the engine speed during field operation 

(RPMFES), the operator must record the engine speed 

Table 2. Measured and predicted fuel consumption.*

Fuel consumption (gal/h)

Traditional 

estimate

(eq (1))

General 

prediction

(eq (2)-(3))

Specific 

prediction

(eq (4))

Actual test 

data

PTO power test, rated 5.102 7.236 6.882 6.821

Drawbar test, maximum pull, rated 5.102 7.236 6.882 6.714

Drawbar test, 75% pull, full throttle 5.102 6.162 5.916 5.916

Drawbar test, 75% pull, reduced throttle 5.102 5.397 5.183 5.185

Drawbar test, 50% pull, full throttle 5.102 4.895 4.776 4.776

Drawbar test, 50% pull, reduced throttle 5.102 4.149 4.027 4.031

*Fuel consumption measured and predicted by the “traditional,” “general,” and “specific” models for Nebraska OECD Tractor Test 1725 

– Summary 225 (shown in figure 1).
7

with the throttle fully open and under typical field load. 

This engine speed is used to estimate the ratio of rated 

power being used. The rated engine speed (RPMRATED) 

is typically found on the tractor’s tachometer, operator’s manual, or NTTL report.

Using the relationship below, the estimated ratio of 

rated power that is being used during field operation is 

computed:

X = (RPMHI − RPMFES)/(RPMHI − RPMRATED) (5)

where

RPMHI = high-idle engine speed (rpm),

RPMRATED = rated engine speed for the tractor being 

considered (rpm),

RPMFES = field engine speed during field operations at 

full throttle (rpm).

This relationship assumes that the governor response 

(engine droop on the right side of figure 3) is linear. 

If this is not the case, use speed ranges found in the 

“Varying Power and Fuel Consumption” section of the 

NTTL report to estimate the ratio of rated power.

For example, suppose that a JD7610 model tractor 

is being used for primary tillage and the field engine 

speed is 2,150 rpm. From the test report (figure 1) and 

field testing, the high-idle speed is 2,267 rpm and the 

rated engine speed is 2,100 rpm. The equivalent power, 

calculated from equation (5), being used for this operation is 0.7, and using the specific coefficients from the 

example in appendix A, the fuel-use equation becomes

Q = (0.039X + 0.0203) ∙ [1 − (N − 1) ∙ (0.5247X − 

0.9345)] ∙ 115.96 hp

At full throttle (N = 1), the estimated fuel consumption 

for primary tillage with the JD7610 is

Q = (0.039 ∙ 0.7 + 0.0203) ∙ 115.96 = 5.52 gal/h

To estimate the savings from employing the gear-up 

and throttle-down practice (Grisso and Pitman), the 

operator can look at several engine reduction possibilities and match with the most appropriate. If the tractor 

engine speed is reduced by 10 percent and 20 percent 

(N = 0.9 and 0.8, respectively), the decrease of fuel 

consumption is estimated as:

D10 = 1 − {(0.9 − 1) ∙ [(0.5247 ∙ 0.7) − 0.9345]}

D10 = 0.943, or a 5.7 percent fuel savings for reducing 

the throttle by 10 percent.

Likewise,

D20 = 0.887, or an 11 percent fuel savings for reducing 

the throttle by 20 percent. 

In terms of fuel consumption rate,

Q10 = 5.52 ∙ 0.943 = 5.21 gal/h, or a savings of 0.31 gal/h,

Q20 = 5.52 ∙ 0.887 = 4.90 gal/h, or a savings of 0.60 gal/h.

The easiest way to reduce the engine speed is from the 

no-load condition (at high idle). A 10 percent and 20 

percent engine-speed reduction would require moving 

the throttle from high idle (2,267 rpm) to 2,040 rpm and 

1,813 rpm, respectively.

Estimating Fuel Consumption 

From Field Operations

The impact of individual operations of cropping systems for a 350-acre grain/pasture cropping system is 

examined and compared. The farm is separated into 

125 acres for haying operations and 225 acres for traditional corn production using a 100 hp tractor. Table 3 

provides the operations that the tractor performs for the 

grain/pasture operations. Note that the tractor is used 

for slightly more than 240 hours annually. The estimated fuel consumption using the “traditional” method 

would be 4.4 gal/h, irrespective of the type of operation; the total fuel use on the 350 acres would be 1,064 

gallons. 

When the “general” model (equations (2) and (3)) is 

applied for each operation and the load factor is taken 

into consideration for different field operations that do 

not require full power, the fuel consumption is estimated at a total of 904 gallons. It is interesting to note 

that the gallons per acre estimates can be compared 

with table 1, and the planting operation appears to consume more fuel than other uses (0.64 versus 0.51 gal/

ac). This approach gives producers potential areas to 

adjust and manage their systems, as well as to optimize 

their machinery systems based on operating averages.

When the GUTD practice is used in these operations, 

with only a 20 percent reduction in speed (some operations can probably be dropped further based on the load 

level), it is estimated that a fuel savings of 87 gallons is 

possible. This translates into a fuel savings of 10 percent for this tractor annually.
8

Conclusion

Three methods for estimating tractor fuel consumption are presented. Comparing estimated and measured 

fuel consumption shows that the fuel consumption estimated using the “specific” model agrees best with the 

measured fuel consumption. This model has the capability to predict fuel consumption when the tractor is 

fully or partially loaded and when the engine speeds are 

reduced from full throttle.

References

ASABE. 2006. ASABE Standards: Agricultural Machinery Management Data. ASAE EP496.3 FEB2006. St. 

Joseph, Mich.: ASABE. http://asae.frymulti.com/standards.asp (accessed Dec. 29, 2009).

ASABE. 2009. ASABE Standards: Agricultural Machinery Management Data. ASAE D497.6 JUN2009. St. 

Joseph, Mich.: ASABE. http://asae.frymulti.com/standards.asp (accessed Dec. 29, 2009).

Siemens, J. C., and W. W. Bowers. 1999. Machinery 

Management: How to Select Machinery to Fit the Real 

Needs of Farm Managers. Farm Business Management 

Series. Davenport, Iowa: John Deere Publishing.

Original Sources of Fuel Predictions

Grisso, R. D., M. F. Kocher, and D. H. Vaughan. 2004. 

Predicting tractor fuel consumption. Applied Engineering in Agriculture 20(5): 553-61. http://bsesrv214.

bse.vt.edu/Grisso/Papers/Fuel_Prediction_DS.pdf

(accessed July 19, 2010).

Grisso, R. D., D. Vaughan, and G. Roberson. 2008. Fuel 

prediction for specific tractor models. Applied Engineering in Agriculture 24(4): 423-28. http://bsesrv214.

bse.vt.edu/Grisso/Papers/pm3122.pdf (accessed July 

19, 2010).

Additional Reading Materials

Grisso, R., and R. Pitman. Five Strategies for Extending Machinery Life. VCE publication 442-451. http://

pubs.ext.vt.edu/442-451 (accessed July 10, 2009).

Grisso, R., and R. Pitman. Gear Up and Throttle Down: 

Saving Fuel. VCE publication 442-450. http://pubs.ext.

vt.edu/442/442-450/442-450.pdf (accessed June 17, 

2010).

Grisso, R., D. Vaughan, J. V. Perumpral, G. T. Roberson, R. Pitman, and R. M. Hoy. Using Tractor Test 

Data for Selecting Farm Tractors. VCE publication 

442-072. http://pubs.ext.vt.edu/442-072 (accessed July 

10, 2009).

Table 3. Fuel consumption estimates for field operations using a 100-hp tractor.

Acres 

per 

hour X† Acres

Full 

(gal/h)

Reduced 

(gal/h)

Gallons 

per acre

Total 

gal Save

Labor 

hours

225-acre, minimum tillage corn for grain

15-ft no-till drill (cover crop) 7.6 0.75 225 5.2 4.6 0.68 154 17.8 29.6

30-ft sprayer (2-X) 15.0 0.35 550 3.4 2.9 0.23 125 18.3 36.7

15-ft, 6-row planter 7.0 0.60 225 4.5 4.0 0.64 145 16.1 32.1

125-acre pasture (haying: two cuttings)

12-ft mower/conditioner* 6.0 0.50 250 4.1 4.1 0.68 171 0.0 41.7

12-ft tedder 7.1 0.20 250 2.8 2.3 0.39 99 17.6 35.2

12-ft side-delivery rake 7.1 0.20 250 2.8 2.3 0.39 99 17.6 35.2

Round baler* 8.0 0.40 250 3.6 3.6 0.45 113 0.0 31.3

 Total 904 87.4 241.8

*Denotes that because PTO driven, the engine cannot be reduced in speed.

†

Fraction of equivalent PTO power available.
9

For tractor test information, contact:

University of Nebraska Tractor Test Laboratory

35 & East Campus Loop

P.O. Box 830832

Lincoln, NE 68583-0832

(402) 472-2442

Fax: (402) 472-8367

http://tractortestlab.unl.edu/ 

E-mail: tractortestlab@unl.edu

Acknowledgments

The authors would like to express their appreciation 

for the review and comments made by Bobby Clark, 

Extension agent, agriculture and natural resources, 

Shenandoah County; Matthew Lewis, Extension agent, 

agriculture and natural resources, Northumberland 

County; Christian Mariger, instructor, biological systems engineering, Virginia Tech; and Mike Kocher, 

associate professor, University of Nebraska-Lincoln.

Appendix A. Coefficient determination for equation (4) for specific tractor.

a = (Q75F − Q50F )/[PPTO (X75F − X50F)] (6)

b = (Q75F/PPTO) − aX75F (7)

c = (f/h − e/g)/(X75F − X50F) (8)

d = cX50F + f/h (9)

e = 1 − [(X75F ∙ Q75R)/(X75R ∙ Q75F)] (10)

f = 1 − [(X50F ∙ Q50R)/(X50R ∙ Q50F)] (11)

g = (RPM75F − RPM75R)/RPM75F (12)

h = (RPM50F − RPM50R )/RPM50F (13)

where

Q = diesel fuel consumption (gal/h),

X = ratio of equivalent PTO power to rated PTO power 

(decimal),

N = ratio of reduced- and full-throttle engine speeds at 

operating load (decimal), 

RPM = engine speed for partial loads from full and 

reduced throttle (rpm),

PPTO = rated PTO power (hp).

The specific subscript refers to the condition of the test, 

where the tractor tests were conducted at full throttle 

(F) and reduced throttle (R) during the 50 percent and 

75 percent drawbar load tests. For example, Q75F is the 

fuel consumption at 75 percent drawbar load and full 

throttle. The method used the fuel consumption data, 

power levels, and engine speed from four partial-load 

drawbar load tests and the PTO and drawbar power at 

rated engine speed. The equivalent power ratios (at the 

four test points) were computed from maximum drawbar power at rated engine speed and the current power 

level. 

As an example, below are the coefficients developed 

using equations (6) through (13) for the tractor test 

Summary 225 (shown in figure 1):

PPTO = 115.96 hp

PMaxDB = 96.26 hp

RPM50F = 2,221 rpm

Q50F = 51.48 hp/(10.78 hp-h/gal) = 4.78 gal/h

X50F = 51.48 hp/96.26 hp = 0.535

RPM75F = 2,190 rpm

Q75F = 75.72 hp/(12.8 hp-h/gal) = 5.92 gal/h

X75F = 75.72 hp/96.26 hp = 0.787

RPM50R = 1,685 rpm

Q50R = 51.60 hp/(12.80 hp-h/gal) = 4.03 gal/h

X50R = 51.60 hp/96.26 hp = 0.536

RPM75R = 1,665 rpm

Q75R = 75.86 hp/(14.63 hp-h/gal) = 5.19 gal/h

X75R = 75.86 hp/96.26 hp = 0.788

a = 5.92 gal/h − 4.78 gal/h = 0.039 gal/hp-h 115.96 hp (0.787 − 0.535)

b = 5.92 gal/h − (0.039 ∙ 0.787) = 0.0203 gal/hp-h 115.96 hp

e = 1 − 0.787 ∙ 5.19 gal/h = 0.1251

 0.788 − 0.92 gal/h
10

f = 1 − 0.535 ∙ 4.03 gal/h = 0.1578

 0.536 ∙ 4.78 gal/h

g = (2,190 − 1,665 rpm)/2,190 rpm = 0.2397

h = (2,221 − 1,685 rpm)/2,221 rpm = 0.2413

c = (0.1578/0.2413) − (0.1251/0.2397) = 0.5247

 (0.787 − 0.535)

d = (0.5247 ∙ 0.5350) + (0.1578/0.2413) = 0.9345

Substituting the coefficients a, b, c, and d in equation 

(4), the final prediction equation for JD7610 becomes: 

Q = (0.0390X + 0.0203) ∙ [1 − (N − 1) ∙ (0.5247X − 

0.9345)] ∙ 115.96 hp

This equation can be used to predict the fuel consumption when a JD7610 is used for different field operations with varying loads and engine speeds. For ease 

of calculations, an Excel spreadsheet (figure A-1) with 

this example has been posted at: http://filebox.vt.edu/

users/rgrisso/Tractor.htm; users can insert their own 

data from the Nebraska Tractor Test Laboratory report. 

Figure A-1. Spreadsheet for calculating the coefficients a, b, c, and d for equation (4).