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Added weight to front of tractor

  1. Dec 17, 2014 #1
    Hey Everyone,

    This is a continuation to the 'increasing front tyre of tractor' project.
    This is a new approach I'm looking at, as I came to the conclusion that increasing the size of the front tyre would effect the drive chain negatively, and was not cost effective and essentially wouldn't resolve the issue.

    The issue still remains, getting stuck in mud, getting stuck attempting to climb mounts of rubble (coal) and I believe adding additional weight to the front of the tractor for a more even weight distribution thus ensuring better traction to the front wheels could help resolve this issue.

    But I'm struggling to find 'hard' evidence to back my theory and even more so, calculations the justify that it would work. Anyone have information/equations that could help me?

    Any help would be greatly appreciated.
     
  2. jcsd
  3. Dec 18, 2014 #2

    Bystander

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    What are typical and maximum depths of mudholes? How high (deep) are the loose rubble piles, and what's the fragment size distribution?
     
  4. Dec 18, 2014 #3
    Unless your front wheels are starting to spin I can't see that adding wieght will solve your problems.
     
  5. Dec 18, 2014 #4
    What model tractor are you using? Have you contacted the manufacturer or a sales engineer?
     
  6. Dec 18, 2014 #5

    Danger

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    From my experience with various terrains, I can pretty much say that adding weight will be counter-productive. What you need to add is width. Think "floatation" tires.
     
  7. Dec 18, 2014 #6

    Baluncore

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    Is it a 2WD or 4WD tractor?
     
  8. Dec 18, 2014 #7

    Danger

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    Now there's a good question. I have been assuming front 2 or 1 WD because of the way that the question was posed. If not, why such emphasis on the front?
     
  9. Dec 18, 2014 #8
    Well that is exactly what is happening, pulling 8 tons plus ungerground. So front rises, then when encountering deep mud, or tall coal piles the front tires start to spin.


    If I may ask, why do you say it is counter productive?

    It is 4WD, with differentials separately on the front and back ie. no central differential.
     
  10. Dec 18, 2014 #9

    Bystander

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    If you can spin the front wheels and there's no differential in the transfer case, you've got a "busted gear box."
     
  11. Dec 18, 2014 #10
    No, there is a differential. Between the front, and between the back. Just not a 'central' differential ie. no diff linking the front and the back.
     
  12. Dec 18, 2014 #11

    Danger

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    Partially because I didn't fully understand until your last post what the problem is. You never mentioned that the front was pulling a wheelie. That normally happens only in a rear-wheel drive system. In a proper setup, neither the front nor the rear rises more than the other upon acceleration.
    This might sound a little odd, but I'm dead serious about it. Go to the top of the Mechanical Engineering forum page, click on Automotive Engineering, and check in with Ranger Mike, particularly in regard to his "race car suspension" course. He knows more about this kind of stuff than anyone else on PF. What works in racing works in industry as well.
     
  13. Dec 18, 2014 #12

    Bystander

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    Front wheels spin and rear wheels don't?
     
  14. Dec 18, 2014 #13
    That is correct. The pull extremely heavy loads, increasing the traction in the rear. But then when facing obstacles, the front lift and spin.
     
  15. Dec 18, 2014 #14

    Bystander

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    No power to rear wheels means busted gear box, or something, somewhere in the drive train.
     
  16. Dec 18, 2014 #15
    No, think your misunderstanding.The rear wheels work (rotate), but the front wheels don't have traction, causing them to spin.
     
  17. Dec 18, 2014 #16

    Bystander

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    You have stated that there is no differential between the front and rear axles. If that is the case, and the drive train is not broken between the front and rear, the total rotations of shafts for front and rear axles must be the same.
     
  18. Dec 19, 2014 #17
    Okay, your correct. I misunderstood.
    But the major issue here is that the front is lifting of the ground, due to the loads they are towing.
     
  19. Dec 19, 2014 #18

    Baluncore

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    When a vehicle climbs a hill, a significant part of the weight of the vehicle is transferred from the front to the rear wheels. Maximum traction is required when climbing steep inclines, so moving ballast to the front of the tractor is a good move. If possible, use water ballast in all tyres. When climbing steep inclines, both front and rear wheels should start to slip at the same time. Where possible, the front tyres can be kept on the ground by lowering the hitch point.

    This is where it gets interesting. When an agricultural tractor is ploughing, the maximum draw bar force and best overall efficiency is obtained when wheel slip is present. If I remember correctly, optimum slip is about 10%. Your tractor may already be operating close to optimum. Are you sure the rear wheels are not also slipping at the same rate as you observe on the front wheels? they are connected by the drive train.
    http://www.nswfarmers.org.au/__data...ing-wheel-slip-to-achieve-fuel-efficiency.pdf
    http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/eng5240

    Wider floatation tyres do not help traction in muddy conditions. I had wide tyres on my 4WD, it would not climb muddy hills. I changed to narrower tyres and the problem is solved because it can displace the surface mud to find grip below. Tractor tyres have diagonal lugs so they will cut through the surface mud by displacing it sideways. Traction is better once the ground is confined by compression. Wide tyres are really only useful in deep soft sand.
     
  20. Dec 19, 2014 #19

    NascentOxygen

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    Is tyre wear going to take a hit when operating with constant slip?
     
  21. Dec 19, 2014 #20

    Baluncore

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    It would if the surface was dry, abrasive and solid, but to plough land to grow a crop requires the ground have small soil particles and water. The slip is a shear zone of rotating particles in the soil rather than a destructive dry rubber on rock slip. Water is a natural lubricant with rubber tyres. The optimum percentage slip computed for agricultural tractors includes the cost of fuel, the driver's time and tyre wear.

    The OP here is I think lifting the front wheels clear of the ground when climbing steep rises. The wheel slip is hard to estimate without wheel-ground contact, so the first move should be to ballast the tractor correctly and then use the lowest possible tow point on the tractor. Tractor directional control and safety is improved by having four wheels in contact with the ground rather than using brake or skid-steering on the rear drive wheels only.
     
  22. Dec 19, 2014 #21
    your problem lies with rear load distribution. the towed trailer is not balanced correctly. even a two wheel harvester trailer needs balance so it doesn't flip the tractor as soon as it tries to move. as long as the amount of weight from the trailer tries to sink the hitch instead of pull back on it your front wheels will want to rise too much to get any traction on loose terrain.
    in the case of a hay trailer with 4 wheels if the attachment bar to the trailer is lower than the hitch you'll get the same problem its better for it to be higher at the trailer and tilted slightly downward as it meets the hitch on the tractor this helps to reduce the lift of the front end of the tractor. (the bar being hinged at the trailer)

    @tire slip wear: the ware and tear on tractor tires is almost negligible because the tires are made for this kind of usage. there is a reason they have eight inch deep nobbies/treads.
     
    Last edited: Dec 19, 2014
  23. Dec 20, 2014 #22

    256bits

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    I was going to say the tongue weight on the drawbar should be nearly zero, and axle centric.
    We do not know the terrain, size of mounds, speed of transport, hitch type, etc.
    Perhaps the tug is just undersized for the load of 8 tons or more.
    Adding more ballast may just aggravate the problem even more - the tug has more weight to pull around.

    Problematic posts
     
  24. Dec 20, 2014 #23

    Baluncore

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    What do you mean by “axle centric”?

    Consider the situation where the projected line of the trailer draw-bar axis passes through the point on the ground mid-way between the tractor rear tyres. The tractor rear axle torque will then not tend to lift the front of the tractor.

    There will however then be a tendency for the trailer draw-bar to lift the rear wheels of the tractor which would transfer weight from the tractor rear axle to the front axle of the trailer. There will be a compromise situation somewhere between the two, but the hitching point should still be kept as low as possible.

    Every ton of ballast added to the tractor will reduce the payload of the combination by one tonne.
    What does it matter if the front wheels are doing no work, so long as the rear wheels are still providing traction.

    Remember that it is the rear axle torque that lifts the front of the tractor. It is hitching low that reduces the tendency for the front wheels to lift. Hitching high tends to kill the operator, it lead to the development of ROPS. A tractor can flip backwards faster than the operator can realise it is happening. Hitching at or above the rear axle height is really foolish and deserves the Darwin Award.
     
  25. Dec 20, 2014 #24
    only the oldest of tractors had hitches near the height of the axle and those are covered in weeds in fields because they have killed so many operators.
    what i said before where you want the trailer bar slightly on a downward slope towards the hitch (and yes a low hitch on the tractor) gives you the best results for four wheels staying on the ground.
     
  26. Dec 22, 2014 #25

    Averagesupernova

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    Couple of things. For those who say adding weight does nothing but reduce available payload, take a look at this. http://www.dreamstime.com/stock-images-tractor-weights-agriculture-image28802884
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    Just google "tractor weights". Adding weight to the front end of a tractor is a very very common practice.
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    If the tractor that the OP is describing is lifting it's front end off the ground it tells me that for the size of the tractor its back wheels have enough traction. If the front end is up and the wheels are still spinning out there are three things that can be done. 1) Add weight to the front in order to get the front wheels down so they can also pull. Of course this assumes 4WD. Doing this also puts more weight on the back wheels increasing traction there. Think about it, add 100 pounds to the front and the front still isn't touching the ground we know that weight had to end up on the back end. 2) Change the back tire scheme so it has enough traction to pull the load and live with the front end being up. I would recommend duals. Of course I would still find a way to get the front end down simply for steering. 3) Get a larger tractor.
     
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