Rollover angle of a JD 3720

[Scotty370]

" ...always pays to plan ahead, cause it's hard to work out physics problems under pucker.........." Wise words! And what do you do when the incline-meter 'lies' ? Take it back! ~Scotty

 

[powerstroke444e]

I agree you can't be to safe on hills. I have had to use a winch more than once to save a tractor when it slide on a hill and the pucker factor got a little more than I could handle.

If you notice the state runs with the wheels as wide as possible and most farmers leave the duals on when mowing ditches.

 

[Ken45101]

I have to wonder if the tractor with the batwing didn't sink the lower wheel in soft muck in the ditch. OTOH, the cab adds some topheavy weight.

 

[Johndeere3720]

You know, this really got to me last night so I did some math to figure it out. I collect little diecast tractors so my testing was sucsessful. Since this tread is about your 3720, i'll start with that. It takes 56.25* to tip over a 5' wide tractor. Now I also found out that it goes down 10* with the FEL up. Now you can give or take a few degrees depending on the center of gravity of a tractor. This test was with a diecast 4310 deere and a Diecast BX22 Kubota. A 4' tractor should roll over at 45* and a 6' tractor should roll over at 67.5*. Now i know some may think you are more stable when you widen out the rear tires but it makes it more prone to tipping. With the rear tires spred outwards, a 4' tractor will tip at 33.312* rather than 45*. A 5' tractor will tip at 41.64* rather than 56.25*. A 6' tractor will tip at 49.968* rather than 67.5*.

X" x .694= tip degrees with widend out rear tires (my diecast 4310)
X" x .9375= tip degrees with alighned front and rear end (my diecast BX22)
-10* with FEL all the way up

What I did to get every thing to inches is i measured the width of the diecast tractor, then multiplied that by the scale which gave me inches and feet. Then I had a protractor taped to the back of my desk and used a ruler to hold the tractor's rear tire up. Then since I couldnt see well under the little tractors, I used my camera and found out the exact angle of the tractor's rear wheel right before tipping. To get the exact degrees above I took the angle and divided it by the width of the tractor which gave me the degrees per inch. The reason that the wider rear end will tip easier is that the front end doesnt cover as much, leaving it harder to balance since the wheels aren't aligned properly. That and the top weight of the engine wants to pull the tractor down the hill. Since it is unstable on the front end, it will tip easier. Since I was curious and there are yanmar owners on these forums I found out my Yanmar 169D, which is 40" wide, tips at 37.5* since the tires are all aligned. I also found out that a bobcat 5600 toolcat (5'6" wide) tips at 45* with the FEL down and 35* with the FEL up. And lets not forget the lawn tractors, a JohnDeere X485 tips at 40* with its 44.8" wide stance. This is something that really interested me and since it is a question that is quite common, I thought it was time for an answer. This is what a 14 year old does for fun after homework. It also confused my math teacher.

 

[radman1]

Now i know some may think you are more stable when you widen out the rear tires but it makes it more prone to tipping. With the rear tires spred outwards, a 4' tractor will tip at 33.312* rather than 45*. A 5' tractor will tip at 41.64* rather than 56.25*. A 6' tractor will tip at 49.968* rather than 67.5*.

I love the enthusiasm, but I believe you should recalculate some of your figures. Widening the rear tires, will make it less prone to rollover. That is fact, not fiction. Also you calculations may be correct for diecast tractors. In the real world, the diecast is metal throughout, not so with tractors. The proprotions of the diecast are correct buthe weight distribution maybe different and affects the center of gravity. Also need to figure weight of operator which is above the center of gravity.

 

[newbury]

How much fuel in the diecast tractors?

Were the tires filled?

When they did tip over did the drivers get hurt?

/edit - when I was 14 I was driving tractors on a farm and trying to not quite lift the uphill tire.

 

[Ken45101]

Ahh! The difference between toys and reality, the difference between theory and reality.

On real tractors, the front end is floating (side to side) and doesn't provide resistance to tipping.

As radman said, the center of gravity is the critical issue and that is not duplicated to scale with toys.

Although I have never tipped anything nor come close to it (thankfully), I can say for certain that my Kubota M9540 with rear tires set to maximum width feels a lot more stable on hillsides than my M5040 with rear wheels set to default width.

It's also well recognized that JD and NH skid steers are more stable going uphill than other makes (they have a different weight distribution, which wouldn't show up in toy models).

Your experiments are good and show great interest. But true engineering research requires a lot more attention to ALL details.

Many people have been killed by tractor rollovers. Of course some of them did dumb things, but I really have my doubts that anyone with an ounce of sanity would be on a 65 degree slope! Even if the tractor didn't roll over, it would be sliding sideways.

Ken

 

[ovrszd]

I had a Tiltmeter on my B2910 that R&B gave me. Since my wife was the primary operator at the time and her pucker factor began when she turned the key I thought she would benefit from the meter and she did. I told her to not exceed 15 degrees. She left a lot of roadbank unmowed.

When I got home I took over the mowing. I hadn't ever ran the 2910 so was cautious at first. After a couple mowings I realized that little tractor would run at 25 degrees with minimal caution observed with loaded R4 rears and 60" MMM. I later used the tractor in the timber and several times saw the tiltmeter pegged, way past 25 degrees.

A lot of operators on here talk about not exceeding 15 degrees. If that's your comfort zone so be it. At that angle you are very, very safe on almost any tractor. Some of the older Yanmars, etc., running on narrow tires set in for narrow width look more than a little tippy to me. As was said earlier, after you get a tire in the air a couple times you'll figure out where your tractor's comfort zone is.

One last point, pay more attention to where the rear tires are going than where the front tires are going. Sitting on a smooth sloped grade your rear tires are what's keeping you on your wheels, not the front tires. Until the front axle reaches the limit of it's oscillation the tractor pays little attention to a hole a front tire falls in.

 

[ovrszd]

but I really have my doubts that anyone with an ounce of sanity would be on a 65 degree slope! Even if the tractor didn't roll over, it would be sliding sideways.

Ken

I'm pretty sure my $40K rockcrawler Jeep won't stay on a 65 degree sideslope. It's iffy at 45 degrees and you don't want to stay there very long.

 

[Baby Grand]

The diecast study is interesting and a novel approach. Congratulations to someone trying an empirical approach to a hypothetical problem. My own conclusion, based on the results and personal experience, is that tractors don't scale well from miniatures. This is often the case in nature. Otherwise, we would be overrun by giant ants.

Also, you have to be careful in your enthusiasm how you present your unscaled results, lest somebody think they are going to apply your results directly. When they get hurt based on your data and decide to lawyer up you will know why I suggest caution on that one. Just read any instructions that came with your tractor if you have any doubts. Worse, if you're an ethical person, there's the awful feeling that you have to live with that maybe you are by some stretch even partially responsible for that fools' suffering.

One last point, pay more attention to where the rear tires are going than where the front tires are going. Sitting on a smooth sloped grade your rear tires are what's keeping you on your wheels, not the front tires. Until the front axle reaches the limit of it's oscillation the tractor pays little attention to a hole a front tire falls in.

ovrszd makes an important point regarding stability & tractor design. And when the front axle eventually does bottom on it's stops, things can happen very quickly. This is a good example of what engineers call a "step function". Try to never let things get to that point.

-Jim