Added weight to front of tractor

[DMFisher]

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.

 

[Bystander]

stuck in mud, getting stuck attempting to climb mounts of rubble

What are typical and maximum depths of mudholes? How high (deep) are the loose rubble piles, and what's the fragment size distribution?

 

[Jobrag]

Unless your front wheels are starting to spin I can't see that adding wieght will solve your problems.

 

[Travis_King]

What model tractor are you using? Have you contacted the manufacturer or a sales engineer?

 

[Danger]

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.

 

[Baluncore]

Is it a 2WD or 4WD tractor?

 

[Danger]

Is it a 2WD or 4WD tractor?

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?

 

[DMFisher]

Unless your front wheels are starting to spin I can't see that adding wieght will solve your problems.

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.

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.

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

Is it a 2WD or 4WD tractor?

It is 4WD, with differentials separately on the front and back ie. no central differential.

 

[Bystander]

the front tires start to spin.

no central differential.

If you can spin the front wheels and there's no differential in the transfer case, you've got a "busted gear box."

 

[DMFisher]

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.

 

[Danger]

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

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.

 

[Bystander]

Just not a 'central' differential ie. no diff linking the front and the back.

Front wheels spin and rear wheels don't?

 

[DMFisher]

Front wheels spin and rear wheels don't?

That is correct. The pull extremely heavy loads, increasing the traction in the rear. But then when facing obstacles, the front lift and spin.

 

[Bystander]

No power to rear wheels means busted gear box, or something, somewhere in the drive train.

 

[DMFisher]

No, think your misunderstanding.The rear wheels work (rotate), but the front wheels don't have traction, causing them to spin.

 

[Bystander]

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.

 

[DMFisher]

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.

 

[Baluncore]

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.

 

[NascentOxygen]

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%.

Is tyre wear going to take a hit when operating with constant slip?

 

[Baluncore]

Is tyre wear going to take a hit when operating with constant slip?

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.

 

[dragoneyes001]

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.

 

[256bits]

your problem lies with rear load distribution...

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

The issue still remains, getting stuck in mud, getting stuck attempting to climb mounts of rubble (coal)

That is correct. The pull extremely heavy loads, increasing the traction in the rear. But then when facing obstacles, the front lift and spin.

 

[Baluncore]

I was going to say the tongue weight on the drawbar should be nearly zero, and axle centric.

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 realize it is happening. Hitching at or above the rear axle height is really foolish and deserves the Darwin Award.

 

[dragoneyes001]

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.

 

[Averagesupernova]

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.

 

[Averagesupernova]

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.

I would disagree with this. When the tractor starts to pull the back end will have a tendency to lift. Asking for lots and lots of wheel hop. Best scenario is always weight on the drawbar.

 

[Baluncore]

I would disagree with this. When the tractor starts to pull the back end will have a tendency to lift. Asking for lots and lots of wheel hop. Best scenario is always weight on the drawbar.

You must be new to the sport of tractor pulling. Do not add weight, first optimise tow-point and drawbar length to counter the axle torque.

You can calculate maximum rear axle torque from the tractor power train specifications. You can calculate the maximum forward ballasting needed to counter that maximum torque. There is no reason to exceed that maximum specified ballasting. By changing tow-point and drawbar specifications you can reduce the maximum forward ballasting and so increase payload, or reduce fuel costs.

The lifting of front wheels due to rear axle torque suggests the back wheels have sufficient grip. The problem then should firstly be resolved by optimising drawbar attachment point in a way that counters the axle torque. If the trailer drawbar slopes down towards the rear of the tractor then the lifting effect on the tractor rear can be significantly reduced by simply lengthening the drawbar or by lowering the drawbar attachment point on the trailer to match the tractor.

Adding ballast to the front of a tractor will reduce the weight on the rear wheels once the tractor is back on all four wheels. That is because the added ballast is forward of the front wheels and so the front wheels become a fulcrum for the added forward weight. That is why I always first consider water ballasting front tyres before adding forward mass.

 

[Averagesupernova]

Before I discuss this any more I want to clarify what a drawbar is. A drawbar is the part on the tractor. It is NOT part of a trailer. Usually that is referred to as the tongue.

 

[dragoneyes001]

I would disagree with this. When the tractor starts to pull the back end will have a tendency to lift. Asking for lots and lots of wheel hop. Best scenario is always weight on the drawbar.

a 2-3 degree slope towards the hitch will not create an upward pull on the back wheels yet it will help to keep the trailer weight pulling back on the hitch instead of downwards which makes the tractor wheely its front end. it also helps keep the trailer from popping off the hitch when the tractor heads downhill.