Traction Traction 4x4 vs. 2 wheel drive

   #1  

Anonymous Poster

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Sep 27, 2005
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Any thoughts on the difference in traction on a 20 hp 4x4
tractor and a 30hp 2 wheel drive. Since the 30hp tractor has
larger tires and more weight do you think they may equal out
somewhat? I have some rolling hills on my lot and wondered
if the traction for mowing would be sufficient on the 30hp 2
wheel drive. You seam to be able to buy a used larger two
wheel drive tractor as cheep or cheaper than a smaller 4x4.

Dennis
 
   #2  

MDSteve

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I think the 2wd would be cheaper but it won't work as well with the hills. I have helped get a few larger 2wd tractors out of muddy pastures. I keep my tractor in 4wd because I don't have any pavement and the hills around here are bad when they get wet. Even morning dew can make them unpassable without 4wd.

Steve
 
   #3  

hazmat

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Lots of thoughts /forums/images/graemlins/grin.gif

Below find the physics of the application, draw your own conclusion.

For disccussion sake, assume same coefficient of friction between tire & ground (grass in your case). Also, lets ignore the effects of the differential (2 wd really is 1 wd unless you lock the axle).

The force that can be appied (known as "drawbar pull" in tractorland), is directly proportional to the normal force on the drive wheels.

A reasonable guess is that a 2wd tractor has a 75 rear/ 25 front weight balance, so on flat ground you get 75% of the weight available to help move the tractor. If you lift a heavy implement on the three point or drive forward up a hill this number goes up. If you have a front end loader & lift something heavy or drive backwards up a hill this number goes down.

The math of how much traction you lose / gain on a slope requires a good picture, which I don't have time to do right now.

A 4wd tractor might have a 60 / 40 split. As you load / unload the front & rear tires, it doesn't matter as much traction wise because the other end gains.

The 4wd really shine under varying conditions.

Have you measured the angle of your "rolling hills"?
 
   #4  

WVBill

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</font><font color="blueclass=small">( Since the 30hp tractor has
larger tires and more weight do you think they may equal out
somewhat? )</font>

I'm thinking that the diameter of the tires may not make that much difference. Traction only comes from the amount of the tire tread in contact with the ground. I suppose if someone worked out the formula for horsepower - per - square inch of contact surface you might get the "scientific" answer.

But based on what I've seen my little 14hp 4wd Kubota do v.s. my neighbor's big 'ole David Brown 2wd, I'd go with the 20 HP 4x4 over the 30hp 2wd.
 
   #5  

BB_TX

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I have 27 PTO hp (33 engine if I remember correctly) with 4wd. I (almost) never engage the 4wd when mowing. The only time I do is when I am mowing the fairly steep ditches along my highway frontage and even then usually only if the grass is wet. My pasture rolls somewhat but not enough to need 4wd. It does come in handy when doing dirt work though.
 
   #6  

CTyler

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With dry conditions 2wd would be fine for most things. When you have snow and/or mud it almost necessity. For me 4wd was a no brainer due to snow and mud. I'd be stuck without it until it dries up some. Also if your pulling something that drags quite a bit 4wd is handy to cut down or eliminate wheel slippage.

With the bigger tractor you have bigger tires that will create more contact area. You also have more weight to help traction. The 4wd on the smaller tractor would still have more traction though. Assuming there isn't a huge difference between the two in tires.
 
  
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#7  
OP
A

Anonymous Poster

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Steve
Yes I can understand that. I do believe 4x4 is better. I was
just trying to figure out how much better with different weights.

Hazmat
No I have not measured them. The first is not much maybe
10 - 15 degrees. The second is approximately 25 - 30 degrees.
It does not really need mowing it’s a pass way (road) to the
back of the lot. It’s mostly trees.

Vwbill
I was thinking of the tire width. I was looking at a TC30 with
turf tires which seemed to have wider tires than a B7500 I was
looking at. Maybe not much wider but somewhat.

We have owned the lot for four years and are in the process of
building a house. I’m really starting to look at tractors. My neighbor
was mowing the lot for me. We traded His son being able to ride
his dirt bike on it for mowing. He has a B7500 with MMM. The
lot was used for crops and pasture. I guess I need to ask him if he
needs four wheel drive. Of course he can get around the steep hill
by going through his lot.

THANKS all for the help.
Dennis
 
   #8  

herbenus

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I have no scientific backup for the following statement. But I've heard this more than once from dealers or farmers or someone. I was told that a 4wd tractor will seem like it's as powerful as a 2wd with twice the horsepower. I know this does not add up by any laws of physics. Just repeating what I was told. What I do know is that when I tool around in 2wd on my place, it slips more than in 4wd, and I usually wind up going into 4wd eventually.
 
   #9  

Bird

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One farmer friend with three tractors in the 100hp range (all 2WD) told me he'd never buy another 2WD tractor new; that 4WD in the same size tractor is the equivalent of 25% more power for pulling, plowing, etc. in addition to be less likely to get stuck in muddy spots. I don't know where he got his numbers from, but from a purely unscientific viewpoint, sounds good to me. /forums/images/graemlins/tongue.gif
 

JohnMiller3

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</font><font color="blue" class="small">( 4WD in the same size tractor is the equivalent of 25% more power for pulling, plowing, etc )</font>

Yes, from different Ag tests conducted, and from a number of Nebraska Tractor Tests... the 20-25% is a good Rule-of-thumb figure to use... /forums/images/graemlins/wink.gif

...or stated another way... a MFWD tractor with 20% less horsepower is equivalent to a 2-wheel drive unit with 25% more horsepower... (ex. @ 80 hp MFWD ~~= 100 hp 2-wheel drive unit)
 
 
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