Grubaugh, Elston K.

Valco, Thomas D.

English

Texas A&amp;M Repository

L-2050CONTROLLING TRACTOR WHEEL SLIPFOR EFFICIENT OPERATIONElston K. Grubaugh and Thomas D. Valco*We often say that anyone wasting time or notgetting hi work done is "spinning his wheels." Ifyour tractor wheels lip more than 15 percent, youare wa ting time, fuel and money.Wh el lip is th percentage difference betweendrive wheel speed and ground speed. A tractor tiremu t grip the soil to develop a pulling force. As thetire gets a grip on the soil, some of the rotationalspeed of the tire is 10 t and not changed into groundspeed. The proportion of speed lost is wheel slip,which i expressed as a percent. A wheel that is notlipping is not pulling; to develop pull, a drivewheel must lip. A it provides larger and largerpulling forces, wheel slip must increase.Under most conditions, tractor drive wheelslippage should range between 10 and 15 percent.This is a compromi e for various soil types becauseu ually it is impractical to add or remove muchweight when working different soil types. Mostpeople barely noti e wheel slip of 15 percent or less.I( you notice tire pinning, you could easily have anxtra 10 per ent lippage. That means you spend 11hours doing job you should have finished in 10.You will burn an extra gallon of fuel for every 10gallons the work hould have taken. Slippage alsocauses faster tread wear, and spinning tires are moreprone to cuts from tones and stumps.Drawbar hor epower is reduced by excessiveslippage (at high wheel spin more power iscon umed in the attempt to grip the soil, i.e., morepower i consumed in soil deformation). But,reducing slippage to les than 10 percent results inex e ive soil compaction and an increase in rollingre i tance. Slippage below 10 percent indicateseither too much tra tor weight or too small a load. Atlow wheel lip, exce ive tractor weight increases thetractor's rolling re istance on the soil surface - ittake more power to push the tractor around thefield."Extension agricultural engineers-mechanization, TheTexas A&M University System.21:5Check SlippageYou can check slippage by counting wheelrevolutions with the tractor loaded and unloaded.Choose a typical area in the field and make a markon one rear tractor tire. Bring the tractor up to speedwith the implement working before you pass apredetermined mark such as a scratch or stake in thesoil. Have someone mark the location on the groundwhere the tire completed 10 revolutions under load.Be sure to use the same gear and throttle setting usedfor normal operation.Raise the implement and circle back to thestarting point. This time, with the implementraised, drive the same distance in unworked soil nextto your previous pass. Again count wheel revolu-tions to the nearest quarter-turn between the twomarks on the soil. If you count 10 revolutions, youhave no slippage and need to reduce weight.Calculate wheel slip as follows:Percent slip =(Loaded revolutions - No load revolutions)100 xLoaded revolutionsFor example, if it took 8.5 revolutions to travel the distancecovered in 10 loaded revolutions:I, 10-8.5 1.5Percent s Ip = 100 x--= 100 x-= 15 percent.10 10'\,Factors Affecting SlippageWeight is a major factor in controlling slippage.Before weighting a trabor, a few things must betaken into consideration. The more important onesare: (I) allowable or optimum drive wheel slip, (2)travel speed, (3) tire load rating, (4) avoidance ofexcessive soil companion and (5) load rating ofrollover protective structure (ROPS). If a tractor isweighted too heavily, a rollover may crush the safetystructure.BallastWeight is added to tractors as ballast in three ways.Either dry powdered or liquid ballast can be pumpedinto tires, or cast iron weights can be attached towheels or to the front frame. Because of installationproblems and difficulties in checking pressure, someengineers discourage using dry ballast. Liquidballast should be a calcium chloride solution toresist freezing and provide more weight than plainwater. However, liquid and dry ballast tend tobecome permanent, where cast iron weights (exceptfor extremely large ones) can be removed for lighterwork. There is no difference in performance of equalamounts of the three types of weights.Major tractor manufacturers suggest 130 poundsof total tractor weight per drawbar horsepower as astarting point. Two-wheel-drive tractors need 25percent on the front wheels for pull-type imple-ments, 30 percent in front for semi-mountedequipment and 35 percent for full-mountedequipment. Adjust weight for specific fieldconditions. You don/t need much extra front weightwith pull-type equipment. Take it off. Unnecessaryfront weight makes the tractor harder to steer. Frontwheels roll uphill to climb out of their ruts and youwaste fuel pushing unneeded weight.Four-wheel-drive tractors usually should have 55to 60 percent of their weight on the front wheels.When loaded, some of the weight shifts, equalizingweight on all wheels. However, in very soft or sandysoils, it may be more efficient to have less weight onfront tires to cut rolling resistance, then the rearwheels pull in tracks firmed by front tires.SpeedAnother major factor in slippage is operatingspeed. The draft, or pull, on tillage equipmentincreases with speed, but you may be able to get morework done at a higher speed with less tractor weight.For instance, as a rule of thumb, acres covered in 10hours equals speed in mph times implement widthin feet. A 25-foot tandem disk pulled at 4 mph withexcessive slippage probably would get the sameamount of work done as an I8-foot disk running 5.5mph. Higher fuel consumption for the increaseddraft is offset by reducing rolling resistance, lessslippage and less soil compaction.Most current tractors are designed to develop theirmaximum horsepower at four to six mph. If youmust use a slower gear to get enough power and thenhave too much slippage, reduce implement size orworking depth. Slow speeds (less than fOUf mph)Table 1. Agricultural drive wheel tractor tires used as singles (maximum speed = 20 mph). Figures znparentheses denote ply rating for which loads and inflations are maximum.Tire Ply Tire Load Limits at Various Cold Inflation Pressures. lb. TorqueSize Rating 12 psi 14 psi 16 psi 18 psi 20 psi 22 psi 24 psi 26 psi Factor8.3-24 4 970 1060 1150 1230 1310 1380(4) 0.949.5-16 4 970 1000 1080 1150 1230(4) 0.869.5-24 4 1210 1330 1430 1540 1630(4) 0.9211.2-24 4 1470 1600 1740 1860(4) 0.9011.2-28 4 1560 1710 1850 1980(4) 0.9212.4-24 4, 6, 8 1760 1920 2080(4) 2230 2370 2510 2640(6) 2760 3120@32 0.8912.4-28 4 1880 2050 2220(4) (8) 0.9113.6-24 4 2270(4) 0.8713.6-28 4, 6 2420(4) 2620 2810 2980 3160(6) 0.8913.6-38 4, 6 2810(4) 3040 3250 3460 3660(6) 0.9413.9-36 6 2730 2960 3170 3370(6) 0.9414.9-24 6 2700 2920 3130 3330(6) 0.8614.9-26 6, 8 2790 3020 3230 3440(6) 3640 3830 4010(8) 0.8714.9-28 6 2880 3120 3340 3550(6) 0.8814.9-30 6 2980 3220 3450 3670(6) 0.8915.5-38 6, 8 3160 3410 3660 3890(6) 4110 4330 4540(8) 0.9416.9-24 6, 8 3540 3800(6) 4040 4270 4490(8) 0.8416.9-26 6, 8 3660 3920(6) 4170 4410 4640(8) 0.8616.9-28 6, 8 3780 4050(6) 4310 4560 4790(8) 0.8716.9-30 6 3900 4180(6) 0.8816.9-34 6 4140 4440(6) 0.9016.9-38 6, 8 4380 4700(6) 5000 5280 5560(8) 0.9118.4-16.16 2810(6) 0.7918.4-26 6,8,10 4390(6) 4700 5000(8) 5290 5560 5830(10) 0.8518.4-28 6 4530(6) 0.8618.4-30 6,8,10 4680(6) 5010 5330(8) 5630 5930 6210(10) 0.8718.4-34 6,8,10 4970(6) 5320 5660(8) 5980 6290 6600(10) 0.8918.4-38 6,8,10,12 5250(6) 5630 5990(8) 6330 6660 6980(10) 7880@32 0.9020.8-34 8 6010 6440(8) (12) 0.8720.8-38 8,10 6360 6820(8) 7250 7670(10) 0.8923.1-26 8,10 6280(8) 6730 7160(10) 0.8223.1-30 8 6700 0.8423.1-34 8 7110(8) 0.8624.5-32 10 8180 8700(10) 0.8417.5L-24 6 3390(6) 0.8628L-26 10 7800(10) 0.82and excessive weight cause too much force on thepower train, resulting in a shortened life andexpensive repairs.TiresTires are another major factor in determiningtractor performance. Always maintain recom-mended inflation in front and rear tires and increaseinflation when maximum ballast is used. Use an air-water gauge if you have liquid ballast and place thevalve at the bottom when checking pressure. Thenwash the gauge.When you add ballast, avoid exceeding the loadrating of each tire. The ratings are based on tire sizeand inflation pressure, and are for static tractorweight. Allowance is made for weight transfer fromimplements.Reducing tire pressure is not a good way to reduceslippage. At lower pressure, sidewall bucklingincreases and tires are more likely to slip on the rims.Table I lists tire load limits and inflation pressuresfor modern tractor tire sizes.DualsThe use of dual tires is another method of slippagecontrol. Dual tires provide more flotation, and theweight of extra tires and wheels increases traction.Dual tires have several advantages and limitations.Advantages of dual tires include:• Dual tires, with added ballast, give moreground contact. This reduces slippage, in-creases ground speed, improves work rates,and possibly reduces fuel consumption.• Tractor stability is improved by the greatercontact and tread width.• Operator fatigue is lessened because the rideis smoother.• The use of duals to replace single tires of thesame size increases flotation.• Tractors converted to duals have a higherpotential for all season use. Duals can be usedto meet the high horsepower requirementsfor land preparation, but the tractor can beused with single tires for row crop cultiva-tion.• Duals often permit the use of the tractor underadverse weather and soil conditions whenusing single rear wheels would make fieldwork impractical.Disadvantages of dual rear tires include:• Some tractor axles, bearings and powertrains may be overstressed by dual wheels withresulting serious damage to the tractor.• If the drawbar load is relatively light, thereis no real advantage in dual tires over singletires of the same size, other than reducing soilcompaction.• Dual tires may make the tractor more difficultto turn. If short turns are made, the extremestress on the tread lugs may cause the lugs totear.• In situations requiring duals only a small partof the year, the added cost may not be recoveredin benefits.Remember, there are no universal guidelines forusing or not using dual tires. Each situation must beexamined separately. Your tractor dealer should beconsulted prior to installing duals to make sure thatpower train components can withstand theadditional stress of dual tires.TOO MUCHWEIGHTPROPER WEIGHTFip;urr 1. TVhrn too much wright is llsrd, tirr trackswill br sharp and distincl in thr soil and thnr will beno r7 1idrnce of slippagr. ll'hrn thr tirrs hm/r toolittle weight, trrad marks arr complrtely wiprd outand fonuard progrrss is slowed. A small amount ofslippage occurs whrn thr tirrs haur proper weight.Soil brtwan thr c!rats in the tirr pattrrl1 is shiftrd,but the trrad pattnn is still 7l isiblr.ENG 6-3Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socio-economic level, race, color, sex, religion, handicap or national origin.Cooperative Extension Work in Agriculture and Home Economics, The Texas A&M University System and the United StatesDepartment of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8,1914, as amended, and June30, 1914.5M-8-82, New

Controlling Tractor Wheel Slip for Efficient Operation.

Texas A&M University

L-2050
CONTROLLING TRACTOR WHEEL SLIP
FOR EFFICIENT OPERATION
Elston K. Grubaugh and Thomas D. Valco*
We often say that anyone wasting time or not
getting hi work done is "spinning his wheels." If
your tractor wheels lip more than 15 percent, you
are wa ting time, fuel and money.
Wh el lip is th percentage difference between
drive wheel speed and ground speed. A tractor tire
mu t grip the soil to develop a pulling force. As the
tire gets a grip on the soil, some of the rotational
speed of the tire is 10 t and not changed into ground
speed. The proportion of speed lost is wheel slip,
which i expressed as a percent. A wheel that is not
lipping is not pulling; to develop pull, a drive
wheel must lip. A it provides larger and larger
pulling forces, wheel slip must increase.
Under most conditions, tractor drive wheel
slippage should range between 10 and 15 percent.
This is a compromi e for various soil types because
u ually it is impractical to add or remove much
weight when working different soil types. Most
people barely noti e wheel slip of 15 percent or less.
I( you notice tire pinning, you could easily have an
xtra 10 per ent lippage. That means you spend 11
hours doing job you should have finished in 10.
You will burn an extra gallon of fuel for every 10
gallons the work hould have taken. Slippage also
causes faster tread wear, and spinning tires are more
prone to cuts from tones and stumps.
Drawbar hor epower is reduced by excessive
slippage (at high wheel spin more power is
con umed in the attempt to grip the soil, i.e., more
power i consumed in soil deformation). But,
reducing slippage to les than 10 percent results in
ex e ive soil compaction and an increase in rolling
re i tance. Slippage below 10 percent indicates
either too much tra tor weight or too small a load. At
low wheel lip, exce ive tractor weight increases the
tractor's rolling re istance on the soil surface - it
take more power to push the tractor around the
field.
"Extension agricultural engineers-mechanization, The
Texas A&M University System.
21:5
Check Slippage
You can check slippage by counting wheel
revolutions with the tractor loaded and unloaded.
Choose a typical area in the field and make a mark
on one rear tractor tire. Bring the tractor up to speed
with the implement working before you pass a
predetermined mark such as a scratch or stake in the
soil. Have someone mark the location on the ground
where the tire completed 10 revolutions under load.
Be sure to use the same gear and throttle setting used
for normal operation.
Raise the implement and circle back to the
starting point. This time, with the implement
raised, drive the same distance in unworked soil next
to your previous pass. Again count wheel revolu-
tions to the nearest quarter-turn between the two
marks on the soil. If you count 10 revolutions, you
have no slippage and need to reduce weight.
Calculate wheel slip as follows:
Percent slip =
(Loaded revolutions - No load revolutions)
100 x
Loaded revolutions
For example, if it took 8.5 revolutions to travel the distance
covered in 10 loaded revolutions:
I, 10-8.5 1.5Percent s Ip = 100 x--= 100 x-= 15 percent.
10 10
'\
,
Factors Affecting Slippage
Weight is a major factor in controlling slippage.
Before weighting a trabor, a few things must be
taken into consideration. The more important ones
are: (I) allowable or optimum drive wheel slip, (2)
travel speed, (3) tire load rating, (4) avoidance of
excessive soil companion and (5) load rating of
rollover protective structure (ROPS). If a tractor is
weighted too heavily, a rollover may crush the safety
structure.
Ballast
Weight is added to tractors as ballast in three ways.
Either dry powdered or liquid ballast can be pumped
into tires, or cast iron weights can be attached to
wheels or to the front frame. Because of installation
problems and difficulties in checking pressure, some
engineers discourage using dry ballast. Liquid
ballast should be a calcium chloride solution to
resist freezing and provide more weight than plain
water. However, liquid and dry ballast tend to
become permanent, where cast iron weights (except
for extremely large ones) can be removed for lighter
work. There is no difference in performance of equal
amounts of the three types of weights.
Major tractor manufacturers suggest 130 pounds
of total tractor weight per drawbar horsepower as a
starting point. Two-wheel-drive tractors need 25
percent on the front wheels for pull-type imple-
ments, 30 percent in front for semi-mounted
equipment and 35 percent for full-mounted
equipment. Adjust weight for specific field
conditions. You don/t need much extra front weight
with pull-type equipment. Take it off. Unnecessary
front weight makes the tractor harder to steer. Front
wheels roll uphill to climb out of their ruts and you
waste fuel pushing unneeded weight.
Four-wheel-drive tractors usually should have 55
to 60 percent of their weight on the front wheels.
When loaded, some of the weight shifts, equalizing
weight on all wheels. However, in very soft or sandy
soils, it may be more efficient to have less weight on
front tires to cut rolling resistance, then the rear
wheels pull in tracks firmed by front tires.
Speed
Another major factor in slippage is operating
speed. The draft, or pull, on tillage equipment
increases with speed, but you may be able to get more
work done at a higher speed with less tractor weight.
For instance, as a rule of thumb, acres covered in 10
hours equals speed in mph times implement width
in feet. A 25-foot tandem disk pulled at 4 mph with
excessive slippage probably would get the same
amount of work done as an I8-foot disk running 5.5
mph. Higher fuel consumption for the increased
draft is offset by reducing rolling resistance, less
slippage and less soil compaction.
Most current tractors are designed to develop their
maximum horsepower at four to six mph. If you
must use a slower gear to get enough power and then
have too much slippage, reduce implement size or
working depth. Slow speeds (less than fOUf mph)
Table 1. Agricultural drive wheel tractor tires used as singles (maximum speed = 20 mph). Figures zn
parentheses denote ply rating for which loads and inflations are maximum.
Tire Ply Tire Load Limits at Various Cold Inflation Pressures. lb. Torque
Size Rating 12 psi 14 psi 16 psi 18 psi 20 psi 22 psi 24 psi 26 psi Factor
8.3-24 4 970 1060 1150 1230 1310 1380(4) 0.94
9.5-16 4 970 1000 1080 1150 1230(4) 0.86
9.5-24 4 1210 1330 1430 1540 1630(4) 0.92
11.2-24 4 1470 1600 1740 1860(4) 0.90
11.2-28 4 1560 1710 1850 1980(4) 0.92
12.4-24 4, 6, 8 1760 1920 2080(4) 2230 2370 2510 2640(6) 2760 3120@32 0.89
12.4-28 4 1880 2050 2220(4) (8) 0.91
13.6-24 4 2270(4) 0.87
13.6-28 4, 6 2420(4) 2620 2810 2980 3160(6) 0.89
13.6-38 4, 6 2810(4) 3040 3250 3460 3660(6) 0.94
13.9-36 6 2730 2960 3170 3370(6) 0.94
14.9-24 6 2700 2920 3130 3330(6) 0.86
14.9-26 6, 8 2790 3020 3230 3440(6) 3640 3830 4010(8) 0.87
14.9-28 6 2880 3120 3340 3550(6) 0.88
14.9-30 6 2980 3220 3450 3670(6) 0.89
15.5-38 6, 8 3160 3410 3660 3890(6) 4110 4330 4540(8) 0.94
16.9-24 6, 8 3540 3800(6) 4040 4270 4490(8) 0.84
16.9-26 6, 8 3660 3920(6) 4170 4410 4640(8) 0.86
16.9-28 6, 8 3780 4050(6) 4310 4560 4790(8) 0.87
16.9-30 6 3900 4180(6) 0.88
16.9-34 6 4140 4440(6) 0.90
16.9-38 6, 8 4380 4700(6) 5000 5280 5560(8) 0.91
18.4-16.16 2810(6) 0.79
18.4-26 6,8,10 4390(6) 4700 5000(8) 5290 5560 5830(10) 0.85
18.4-28 6 4530(6) 0.86
18.4-30 6,8,10 4680(6) 5010 5330(8) 5630 5930 6210(10) 0.87
18.4-34 6,8,10 4970(6) 5320 5660(8) 5980 6290 6600(10) 0.89
18.4-38 6,8,10,12 5250(6) 5630 5990(8) 6330 6660 6980(10) 7880@32 0.90
20.8-34 8 6010 6440(8) (12) 0.87
20.8-38 8,10 6360 6820(8) 7250 7670(10) 0.89
23.1-26 8,10 6280(8) 6730 7160(10) 0.82
23.1-30 8 6700 0.84
23.1-34 8 7110(8) 0.86
24.5-32 10 8180 8700(10) 0.84
17.5L-24 6 3390(6) 0.86
28L-26 10 7800(10) 0.82
and excessive weight cause too much force on the
power train, resulting in a shortened life and
expensive repairs.
Tires
Tires are another major factor in determining
tractor performance. Always maintain recom-
mended inflation in front and rear tires and increase
inflation when maximum ballast is used. Use an air-
water gauge if you have liquid ballast and place the
valve at the bottom when checking pressure. Then
wash the gauge.
When you add ballast, avoid exceeding the load
rating of each tire. The ratings are based on tire size
and inflation pressure, and are for static tractor
weight. Allowance is made for weight transfer from
implements.
Reducing tire pressure is not a good way to reduce
slippage. At lower pressure, sidewall buckling
increases and tires are more likely to slip on the rims.
Table I lists tire load limits and inflation pressures
for modern tractor tire sizes.
Duals
The use of dual tires is another method of slippage
control. Dual tires provide more flotation, and the
weight of extra tires and wheels increases traction.
Dual tires have several advantages and limitations.
Advantages of dual tires include:
• Dual tires, with added ballast, give more
ground contact. This reduces slippage, in-
creases ground speed, improves work rates,
and possibly reduces fuel consumption.
• Tractor stability is improved by the greater
contact and tread width.
• Operator fatigue is lessened because the ride
is smoother.
• The use of duals to replace single tires of the
same size increases flotation.
• Tractors converted to duals have a higher
potential for all season use. Duals can be used
to meet the high horsepower requirements
for land preparation, but the tractor can be
used with single tires for row crop cultiva-
tion.
• Duals often permit the use of the tractor under
adverse weather and soil conditions when
using single rear wheels would make field
work impractical.
Disadvantages of dual rear tires include:
• Some tractor axles, bearings and power
trains may be overstressed by dual wheels with
resulting serious damage to the tractor.
• If the drawbar load is relatively light, there
is no real advantage in dual tires over single
tires of the same size, other than reducing soil
compaction.
• Dual tires may make the tractor more difficult
to turn. If short turns are made, the extreme
stress on the tread lugs may cause the lugs to
tear.
• In situations requiring duals only a small part
of the year, the added cost may not be recovered
in benefits.
Remember, there are no universal guidelines for
using or not using dual tires. Each situation must be
examined separately. Your tractor dealer should be
consulted prior to installing duals to make sure that
power train components can withstand the
additional stress of dual tires.
TOO MUCH
WEIGHT
PROPER WEIGHT
Fip;urr 1. TVhrn too much wright is llsrd, tirr tracks
will br sharp and distincl in thr soil and thnr will be
no r7 1idrnce of slippagr. ll'hrn thr tirrs hm/r too
little weight, trrad marks arr complrtely wiprd out
and fonuard progrrss is slowed. A small amount of
slippage occurs whrn thr tirrs haur proper weight.
Soil brtwan thr c!rats in the tirr pattrrl1 is shiftrd,
but the trrad pattnn is still 7l isiblr.
ENG 6-3
Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socio-
economic level, race, color, sex, religion, handicap or national origin.
Cooperative Extension Work in Agriculture and Home Economics, The Texas A&M University System and the United States
Department of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8,1914, as amended, and June
30, 1914.
5M-8-82, New


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Controlling Tractor Wheel Slip for Efficient Operation.

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Controlling Tractor Wheel Slip for Efficient Operation.

Abstract

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Full text

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