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§ 17

Tractor ballast with implement in rear lift

How much front weight should the tractor have with this implement on the back?

Answer: A heavy implement in the rear lift raises the front axle, and then the tractor steers and brakes poorly. Instruction books for lift-mounted implements require that the front axle always carries at least 20 % of the tractor's own weight, and they give a calculation of the minimum front ballast. The calculator works out the minimum front ballast and the front axle load you get with the ballast you have mounted. The figures for the tractor are in its instruction book, and you measure the distances c, d and a yourself.

Formula

GV min = (GH × (c + d) − TV × b + 0,2 × TL × b) ÷ (a + b)

Forakseltryk = (GV × (a + b) + TV × b − GH × (c + d)) ÷ b (momentligevægt om bagakslen)

Samlet vægt = TL + GV + GH, bagakseltryk = samlet vægt − forakseltryk

Requirement: front axle load must be at least 0.2 × TL

Symbols and units in the formula
SymbolMeaningUnit
tlTractor's own weight TLkg
tvFront axle load on empty tractor TVkg
bAxle distance bm
ghTool weight in the rear lift GHkg
cRear axle to lift balls cm
dLifting balls to tool centre of gravity dm
aFront ballast centre of gravity to front axle am
gvAssembled front ballast GVkg
=Minimum front ballast GV minkg
=Front axle load with mounted ballastkg
=Front axle load as per cent of own weight (requirement: minimum 20%)%
=Total weightkg
=Rear axle load with implement and ballastkg

Validity and source

Source
Ballast calculation in implement manufacturers' instruction books (VDMA method, e.g. Pöttinger): front axle must bear at least 20% of tractor's own weight

Does not apply when

  • Also compare total weight, axle load and tyre load rating with the tractor's permitted values in the registration certificate and instruction manual. Weigh the combination if you like. The calculator is not an approval.

Worked example

The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.

Substituted

  • Tractor's own weight TL6,500 kg
  • Front axle load on empty tractor TV2,700 kg
  • Axle distance b2.60 m
  • Tool weight in the rear lift GH2,000 kg
  • Rear axle to lift balls c1 m
  • Lifting balls to tool centre of gravity d1.40 m
  • Front ballast centre of gravity to front axle a1.10 m
  • Assembled front ballast GV600 kg

Giver

  • Minimum front ballast GV min314 kg
  • Front axle load with mounted ballast1,708 kg
  • Front axle load as per cent of own weight (requirement: minimum 20%)26.3 %
  • Total weight9,100 kg
  • Rear axle load with implement and ballast7,392 kg

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Sådan bruger du den

Når en kunde køber en tung plov, en sprøjte eller et andet redskab til bagliften, skal traktoren have nok frontvægt. Forakslen skal altid bære mindst 20 % af traktorens egenvægt, ellers styrer og bremser den dårligt. Beregneren regner den mindste frontballast og forakseltrykket med den frontvægt, kunden har.

Step by step

  1. Find traktorens egenvægt TL og forakseltryk TV i instruktionsbogen, eller vej den tomme traktor.
  2. Mål akselafstanden b og afstanden c fra bagakslen til liftkuglerne.
  3. Find redskabets vægt GH og afstanden d fra liftkuglerne til dets tyngdepunkt i redskabets instruktionsbog.
  4. Mål afstanden a fra forakslen til frontvægtens tyngdepunkt.
  5. Aflæs mindste frontballast, og tjek også samlet vægt, akseltryk og dæk mod de tilladte værdier.

Typical errors

  • At glemme afstanden d til redskabets tyngdepunkt.
  • At bruge totalvægten i stedet for egenvægten.
  • At glemme dækkenes bæreevne.

Examples from everyday life

Plov på 2 tons

En traktor på 6.500 kg med 2.700 kg på forakslen skal have en 4-furet vendeplov på 2.000 kg, hvis tyngdepunkt ligger 1,4 m bag liftkuglerne. Kunden har en frontvægt på 600 kg.

Tractor's own weight TL
6,500 kg
Front axle load on empty tractor TV
2,700 kg
Axle distance b
2.6 m
Tool weight in the rear lift GH
2,000 kg
Rear axle to lift balls c
1 m
Lifting balls to tool centre of gravity d
1.4 m
Front ballast centre of gravity to front axle a
1.1 m
Assembled front ballast GV
600 kg

It means: Mindste frontballast er 314 kg. Med 600 kg er forakseltrykket 1,708 kg, som er 26.3 % af egenvægten. Samlet vægt er 9,100 kg, og bagakslen har 7,392 kg.

Uden frontvægt

Kunden vil prøve at køre med ploven uden frontvægt for at spare brændstof.

Tractor's own weight TL
6,500 kg
Front axle load on empty tractor TV
2,700 kg
Axle distance b
2.6 m
Tool weight in the rear lift GH
2,000 kg
Rear axle to lift balls c
1 m
Lifting balls to tool centre of gravity d
1.4 m
Front ballast centre of gravity to front axle a
1.1 m
Assembled front ballast GV
0 kg

It means: Uden ballast er forakseltrykket 854 kg, kun 13.1 % af egenvægten. Det er under kravet på 20 %.

Rule of thumb

Jo længere redskabet hænger bag ved, jo mere ballast skal der til.

How to check the answer

Forakseltryk + bagakseltryk skal give samlet vægt.