Why 4 Wheel Drive

[LBrown59]

required:

equired but handy.

Locks on
handy, but not required.

I could build houses with hammer and nails and leave the nailguns at home, but they sure are handy. Even to the point that if I want to be competitive, they are required.

A person could farm wheel drive.

My neighbors farm about 1400 acres. They've been farming that land since the 1800's. They started with mules. They have 6 or 7 big 2WD IH's. The last several years they have been buying newer tractors, each 4WD. I think they're on to something.

Could be.

 

[Grrrr]

In the UK, it is actually very difficult to buy a 2WD tractor, so much so that you won't find a new one on any dealers yard across the country - you would have to have one ordered specially from the factory and from what I have heard, the wait time can be six to nine months.

There are still plenty of two wheel drive tractors around of an older generation, which did all the same work that we do today, albeit at a slower pace.

Indeed, the 37HP MF 135 in my avatar once did all the ploughing on 100 acres Today it is done with 265HP 4 wheel drive monstrosity, burning a small container ship worth's of diesel each day.

I used to mow a field with the same 135 with a little bush hog on it. It was a very steep field and my technique was to drive round the side and then go down the slope. When I started to slip I hit the clutch, and freewheeled to the bottom. Not very clever

However, the reason that 96% of UK tractor sales are 4WD is that most people have realised that 4WD is just more efficient for almost every job.

This applies because modern 4WD have a very good turning radius (most of the time you can turn tighter than the drawbar or PTO can withstand) and even if they are going to spend all summer baling hay, in the winter they can then be used to spread dung with a muck spreader.

Also (as I think may have been mentioned before ) all modern tractor will shift into 4WD as soon as you touch the breaks, so when you're driving down the road (which happens a lot more in the UK than the US) and you meet a car, you stamp on the brakes and you stop pretty much immediately.

With 2WD, all the weight suddenly lurches to the front wheels, and you engage in a very long power slide with little way to stop. With an 18 ton trailer behind you, I certainly wouldn't tow it with a 2WD tractor.

Now with a loader, don't even get me started . 4WD is completely necessary (I feel that needs to be emboldened to highlight it's importance!).

Yes, 30 years ago they put loaders on 2WD's, but they were all bloody useless to be honest, especially in the field.

Most of the time they were just used to feed in the yards, or lift bags of fertiliser. Now, we want to use them to load bales in fields or feed cattle or load muck.

If you don't believe me try driving a 2WD tractor with a loader carrying a round bale down a sloping field. I guarantee you will get to the bottom a **** of a lot quicker than you thought you would, and all dropping the loader will do is make a nice skid mark across your field

Anyway, my point being that unless you have very good reason to buy 2WD (like a feed wagon tractor that will never go in a field, or on the road), whatever size tractor you are buying, 4WD is the only sensible choice.

It is interesting that the UK fully embraced 4WD tractor 10-15 years ago, but the USA only seems to have cottoned on in the last 5 or so years.

But then again, considering that the whole point of the three point hitch was to put the most force on the rear wheels, perhaps their was logic behind the madness?

Also, whenever I see a new 2WD tractor today, I just can't help but think it looks pretty silly. Like these two:
I think they just look totally silly.

 

[JasG]

You hit it. You would have to set up a pull point below ground level!!! - Forward of the rears would be a help too. No sweat.
larry

The reason a drawbar is pulling down on the front, is it is attached on any good tractor ahead of the rear axle. The drawbar is only supported at the rear, but the pin on most tractors is ahead of the axle. Most things you would pull, there attachment point is at the same height or very close to it, so it's pulling straight back not pulling from the ground like a pull sled. Balers, forage harvesters, mowers etc most have adjustable hitches to help with this effect. If you are pulling from the ground like skidding logs, or the 3 point hitch then that will pull down on the rear and lighten the front.

 

[SPYDERLK]

The reason a drawbar is pulling down on the front, is it is attached on any good tractor ahead of the rear axle. The drawbar is only supported at the rear, but the pin on most tractors is ahead of the axle.

The wheels apply force at the ground. If the load applies resistance above the ground you cant be pulling the front of the tractor down.
larry

 

[wolc123]

I like that post from the UK. You are right on that it has taken much longer for us "colonials" to fully embrace the 4wd, me especially. This crazy, high-priced oil we got now has pretty much delivered the knockout blow to the big, heavy, 2wd's that many of us had clung to for so long, and you better believe that fuel economy alone is plenty to justify 4wd for anyone who does any significant ammount of tillage. Those big 2wd's are selling at auctions today for very close to scrap value in many cases, while 4wd's still command a premium. Two jobs that I would have never believed could be so much easier since getting 4wd, 4 years ago are loader work and disking. I seriously think my fuel consumption while disking is half what it was with 2wd. I thank my lucky stars every day that I got rid of my big, old, 2wd before this crazy oil thing started.

 

[Duffster]

. Those big 2wd's are selling at auctions today for very close to scrap value in many cases,

Really

At scrap price I will take as many as you can get me.

Please show the numbers on your fuel savings also.

 

[Turbys_1700]

Lots of folk around here are still utilizing 2WD's very efficiently on the farm. I owned the first 4 wheel assist tractor on our farm. The 4 wheel assist is of most beneficial to smaller compacts while larger farm tractors can be efficient with 2 WD for haying and the such. I guess the evolution of the tractor now has 4WD as a must but for larger farm tractors 2WD units can do fine. I can tell you that I was amazed at what my little 1720 can do pulling a box blade with the 4 wheel assist on.

 

[Grrrr]

Really

At scrap price I will take as many as you can get me.

Please show the numbers on your fuel savings also.

I don't actually have any numbers, and I don't want to get into an argument, but when I am pulling a plough, I can tell you in 4WD maybe you get 10 - 20 % wheel slip.

With 2WD, I would get more like 30 - 40 %.

To me, that would suggest that running at the same engine speed, the 4WD tractor is going to get to the other headland quicker, and hence spend less time burning diesel. Over the course of a day, that could be 60 litres.

And secondly, when the ground conditions are less than ideal, 2WD tractors I find tend to plow around a bit when trying to turn at the headland, whereas 4WD just pulls straight around no problem.


Strangely in the UK, decent 2WD tractors of 10 years old or less actually make quite good money, because there are so few of them (apparently only 23 2WDs were sold last year). They are popular with some farmers for running of feeder wagons.

However, there are hundreds and thousands of relatively big 2WDs from the 70s and 80s that do command basically scrap prices, they are heavy, slow, burn diesel and are basically useful to UK farming today. But there prices stay up slightly because they are popular with collectors and the export market.

But a 80's 100HP 4WD tractor will still command excellent money as it has farm more use on the farm, or can be fitted with a loader and then becomes very useful to have around.

Wrongly or rightly, 2WDs have basically been relegated to run a bout duties in the UK.....

 

[JasG]

This my opinion, but I think 4wd didn't catch on here till I would say 10-12 years ago in farming due to the 1st ones were so poorly designed. It was usually an after though add on unit and were a larger hassle than benefit. Some examples would be the John Deere front wheel assist on the 20 - 40 series. All it did was assist you at getting more stuck and over heat your hydraulic system. It turned good, but the front tires were either going too slow or too fast. I spent a lot of time on a 4440 with the system, if you only used it in bursts when you were already having traction issues and turned it off after, it worked OK. For tillage you wouldn't want to leave it on all the time due to heating and tire wear. The 1st IH with MFWD were just as bad but for other reasons. They didn't have planetary hubs like the tractors of today. If you were on hard ground, or the road and didnn't switch it off it would snap the axle or drive shaft. Other than Deere until the early 90's it took a huge area to turn them around. Case and Ford came out with later 4wd drives that weren't much better. IH 86 models with 4wd had a rough ride.
The 50 series Deere's and the 2nd generation CaseIH Magnum were the 1st I think that made it worth getting. Some others may have gotten it right to, my experince is mostly with Deere, CaseIH throught that time. Now I think most make a good well made 4wd that can turn and be a real aid.

 

[EE_Bota]

First: 4wd.. I have seen times where if the front wheels could dig even a little bit, I would not be stuck. Since I didn't have front wheel drive, I literally took a shovel and dug out in front of the front tires and came out.

Second: It MAY be not be true for all tractors, and for all geometries, but some tractors can pull down on the front end. If you look at the details of the "Ferguson system," when it was introduced, they made that claim.
Many older tractors had a tremendous coil spring behind the bracket that the top hitch attached to. That spring had to be compressed to get draught control (up) action. If you look at the geometry of the situation, it would appear that tractor can apply down pressure on the front end in some cases.

I will dare say that any tractor pulling a three point hitch load where the pulling force is more than the weight of the implement, it will create a down force on the front end. The attachment points of the lift arm are below the axle level, therefore that creates down force (under the circumstances I described.) Also, the top link is well above the axle, therefore that will also create down force on the front end. Bear in mind, that even if the front end comes up off the ground, this is STILL true because the front end would have come up earlier and further than if it had not had the system.
In the words of my logic professor "Now, go home and convince yourself this is true."

Yesterday's Tractors - Ferguson System Principal and Theory of Operation

 

[SPYDERLK]

Second: It MAY be not be true for all tractors, and for all geometries, but some tractors can pull down on the front end. If you look at the details of the "Ferguson system," when it was introduced, they made that claim.
Many older tractors had a tremendous coil spring behind the bracket that the top hitch attached to. That spring had to be compressed to get draught control (up) action. If you look at the geometry of the situation, it would appear that tractor can apply down pressure on the front end in some cases.

I will dare say that any tractor pulling a three point hitch load where the pulling force is more than the weight of the implement, it will create a down force on the front end. The attachment points of the lift arm are below the axle level, therefore that creates down force (under the circumstances I described.) Also, the top link is well above the axle, therefore that will also create down force on the front end. Bear in mind, that even if the front end comes up off the ground, this is STILL true because the front end would have come up earlier and further than if it had not had the system.
In the words of my logic professor "Now, go home and convince yourself this is true."

Yesterday's Tractors - Ferguson System Principal and Theory of Operation

Note that the description is regarding ground engaging implements. All of their resistance to motion is at or below ground level. So yes in that instance the front end is pushed down. The distance below ground the force is applied times the force applied by the tires at ground level is the net torque trying to rotate the tractor forward [front tip]. If the resisting force is at ground level there is no net torque. If above ground there is net torque trying to back tip the tractor. In each case these torques are proportional to the vertical distance from the level at which the tractor exerts horizontal force to the level at which the load exerts horizontal force.
larry

 

[JasG]

Spyderlk

I think you are mistaking the source of the force vs the point it is applied. The source of the force and pivot point on a tractor is the rear axle. It is exerted at the ground but the torque trying to lift the front is from the center of the axle. So pulling below that point will try and counter the force trying to tip the tractor over. If this were not the case tractors would not be able to pull the loads they do without massive counter weights on the front of the machines. Think about a tractor starting off pulling a load up an incline. If what you are explaining is true, it would almost not be possible.

 

[/pine]

When you get a 4 wheel drive stuck...it's really stuck...!

 

[SPYDERLK]

Spyderlk

I think you are mistaking the source of the force vs the point it is applied. The source of the force and pivot point on a tractor is the rear axle. It is exerted at the ground but the torque trying to lift the front is from the center of the axle. So pulling below that point will try and counter the force trying to tip the tractor over. If this were not the case tractors would not be able to pull the loads they do without massive counter weights on the front of the machines. [[Think about a tractor starting off pulling a load up an incline. If what you are explaining is true, it would almost not be possible.]]

[[How do you figure that?]].

Nothing I said prevents a tractor pulling a load up a hill. The hill just lightens the front a bit more.

The tires apply force rearward and the axles apply the same force forward into the tractor body. Force resisting motion of the tractor [for acceleration or pulling a load] has effect based on where relative to the ground that force is applied. That resisting force is applied at the tractor Center of Mass [pretty high]for acceleration or when climbing hills. It is applied at the level of the hitch point when pulling a load at steady speed. Accel and/or a hill will still increase the tendency to tip back regardless of the hitch level because of the high COM.
larry

 

[jagyzf]

[[How do you figure that?]].



The tires apply force rearward and the axles apply the same force forward into the tractor body. .
larry

Your thinking is incorrect. Axles only apply rotational force, it is neither forward or backward force. In the case of going forward the axle is trying to rotate the tires in one direction, the frame in the opposite. The force of gravity pulls down on the front end forcing the tires to rotate and move forward. The drawbar being below the axle is trying to counter this force of lift. I have had this covered in several farm safety courses I have taken over the years. It is why it is recommened to always when pulling, other than a 3 point impliment, connect to the drawbar. Also when possible not to pull from the ground because the load wants to line up with the point of attachment to the tractor to create a straight line of pull.

The link below explains drawbar leverage and how as the front end of the tractor raises the drawbar counter acts it when pulling straight. If the load is below the the point of pull it helps lift the front until a straight line is formed.

NASD: Tractor Overturn Hazards

 

[JasG]

EE_Bota and Jagyzf your links seems to explain it as it was explained to me many years ago on 3 point and drawbars. One farmer I worked for would put weights on the front of the tractor for plowing due to it was a semi mounted unit and then take them off for disking. He always said that it wasn't needed for anything but plowing due to disks and drags are connected to the drawbar and it was a straight pull. The plows were using only 2 points of the 3 point hitch with an upward pull so it could come up under heavy load. He didn't want to be fighting the none driven front wheels any more than needed over plowed ground for seconday tillage so we would alway pull them off when done and leave them off until time to plow again. I also remember some old timers when I was a teenager discussing how tractors built in and after the 1950's were so much safer than the years before. One of the things they discussed was the drawbar being moved from just attached to the rear axle anyway possible to under and ahead of the axle. Back in the day, by the way they talked it was not uncommon for a tractor to flip over backwards due to different methods of attachment of impliments.

The other items I remember them discussing was the switch away from the narrow front end and a "standard" PTO.

I didn't think about until I read the link on the drawbars, 4wd due to the torque is divided between 2 axles this also makes the tractor less likely to lift the front end. That seems to make some sense. I only throught about the added weight. So that would be another plus for 4wd.

 

[jagyzf]

I think in the future more front mount attachments for tractors of all sizes from Compact all the way up through large farm machines will be made. I don't see many attachments made for 2wd other than loaders. I think the added level of control will make this and even more important option. The newer tractors with the ride controls that can only be purchased on the 4wd.

As Grrr said it's getting to a point that 2wd just doesn't look right anymore. The newer tractors are built to be 4wd 1st 2wd 2nd. Notice in his pictures the contours of the hoods, that looks like to me its for extra clearance for a 4wd to turn sharp.

 

[SPYDERLK]

Your thinking is incorrect. Axles only apply rotational force, it is neither forward or backward force. In the case of going forward the axle is trying to rotate the tires in one direction, the frame in the opposite. The force of gravity pulls down on the front end forcing the tires to rotate and move forward. The drawbar being below the axle is trying to counter this force of lift. I have had this covered in several farm safety courses I have taken over the years. It is why it is recommened to always when pulling, other than a 3 point impliment, connect to the drawbar. Also when possible not to pull from the ground because the load wants to line up with the point of attachment to the tractor to create a straight line of pull.

The link below explains drawbar leverage and how as the front end of the tractor raises the drawbar counter acts it when pulling straight. If the load is below the the point of pull it helps lift the front until a straight line is formed.

NASD: Tractor Overturn Hazards

Obviously no, since the axles are the only connection of the tractor to the wheel, whose traction applies the push. Yes, the tractor tries to rotate backward about the axle. A pull point below the axle resists this and a pull point that is below the axle an amt = to the wheel radius will resist it completely. The drawbar not being this low does not counter it completely until the tractor rears up enuf to bring the pull point [bar end] down to ground level - long bars are pretty safe.
While the link has good info, the pull angle diagram on the stump is totally bogus and discussed in a previous thread.

There is a lot of misinfo out there. The most effective weapon is an inquiring nature and an understanding of physics.
larry

 

[EE_Bota]

JasG, jagyzf, and SPYDERLK: I appreciate the discussion you guys have been having. It is as good a discussion as I have seen yet on TractorbyNet.

I think JasG and jagyzf did such a good job explaining it, that I am free to play with the problem mentally like a little kid instead of trying to explain. (I can't explain worth a darn anyway.)

SPYDERLK said:
"The tires apply force rearward and the axles apply the same force forward into the tractor body. Force resisting motion of the tractor [for acceleration or pulling a load] has effect based on where relative to the ground that force is applied. That resisting force is applied at the tractor Center of Mass [pretty high]for acceleration or when climbing hills. It is applied at the level of the hitch point when pulling a load at steady speed. Accel and/or a hill will still increase the tendency to tip back regardless of the hitch level because of the high COM."


Let's make the tractor simpler. A David Bradley tractor is actually a good model for the hitch attachment question.
This simplifies the COM issue considerably, and I hope it helps clarify the issue a bit. The center of mass issue is mostly gone, but the implement attachment issue still remains.

 

[JasG]

Obviously
There is a lot of misinfo out there. The most effective weapon is an inquiring nature an an understanding of physics.
larry

OK so you have a better understanding of physics that Penn State's Ag Department which is putting out safety misinformation? You also seem to know more than probably every farmer I've ever known.

You know it's not about being right or wrong, I come here to learn and share knowledge if I can. If you want to say others are wrong and don't understand, why don't you show us something other than "your understanding of physics". Others here have been good enough to put links to information that supports there point. All you have done is put up at times gobbldygook, and now you say something that does not agree with you is misinformation. No one with a real understanding of physics would say a rotating shaft of any kind, axle or not puts out a forward force, shaft are for torque. Not only did I take some physics, but I have a job that I actually apply physics in on a regular basis.

You have an inquiring nature, why don't you connect a tractor to something and see for yourself. Or at the very least show us where you are getting your information from.

Look up the Nebraska test data on some tractors. How could a tractor have a drawbar pull almost equal to it's weight if the drawbar didn't keep it from going over? That's pounds of pulling force, not pulling a load on wheels that once moving only takes a few HP to keep the load moving. Going by what you claim the only force counter acting the rotation is the weight over the front axle which on most tractors is 40% or less, any weight on the rear axle would be trying to lift the front end.


EE_Bota - Thank you for the compliment.