Tractor Rollover Myths and Facts

[slowzuki]

RE 1

Eliminates the jerk type rear rollover, significantly reduces the tractive type. During a non jerk type manouve, lift-off is regulated by the moment about the rotation point. We have the mass of the tractor times the distance from rotation point to the centre of mass, we have the drawbar load and we have the tires. The moment of the tires vs the drawbar (couple) are interesting. THe max drawbar pull is at liftoff (on a perfectly ballasted tractor), that is the most the tractor can pull and most drawbar geometrys cause the couple distance to decrease so the tires will slip as the front end comes down.

Now throw in some uneven ground and things get really complicated. A dip the same radius as the tire can radically improve traction for example.


Re the loader,
as you get into bigger and bigger ag tractors the loader lift vs tractor mass falls way off. My 6500 lb tractor can move 2500 lbs to full height. A 20,000 lb tractor generally has a 5000 lb loader on it despite being 3 x heavier. So my tractor is roughly balanced on the front axle at full capacity while the larger tractor still has 5000 lbs to spare on the rear axle at full capacity.

Now in the utility tractor class around 10,000 lbs, they still have those 5000 lb loaders on them. The loaders don't get bigger because normal farm loads are smaller than that. So they need loaded tires, and often ballast when pushing them. Luckily usually they only have a 1200 lb round bale on the loader.

 

[RoyJackson]

Good links! I havnt read them all, but I see an error in Fig5 of Tractor Overturn Hazards:
"Drawbar leverage is another principle of stability/instability related to rear overturns. When a two-wheel drive tractor is pulling a load, its rear tires push against the ground. Simultaneously, the load attached to the tractor is pulling back and down against the forward movement of the tractor. The load is said to be pulling down because the load is resting on the earth's surface. This backward and downward pull results in the rear tires becoming a pivot point, with the load acting as force trying to tip the tractor rearward. An angle of pull is created between the grounds surface and the point of attachment on the tractor. Figure 5 illustrates these points."

I'll be interested in reading your correction. It would be nice if you send your comments to the folks who wrote that article as well.

 

[Soundguy]

The flex links on my hogs offer an amazing 3" maybee 4" of flex. Eventually they do lock up metal to metal. Now.. if you have a chain for a toplink.. or a mower that uses a 'colapsable' aframe with a non rigid link tot he back.. then I agree with yor statement about a flopsy implement. However.. as that applies to the original statement.. I think it should be prefaced that the original statement is presuming a 'rigid' and stout 3pt implement onthe rear. still.. the 'never' thing is a fly in the ointment... as has been mentioned..

Soundguy

The problem with a bush hog is that most of them are attached via flexible toplink connections on the mower. Not sure what the technical term is for that swinging toplink connector but there is little resistance to having the rear of the mower lift (as would happen in a relative sense if the tractor started to rotate on the rear axle) as the linkage is flexible. With a box blade or rake etc that is not the case as the toplink geometry is fixed.

 

[RoyJackson]

Even if an implement didn't inhibit rear rollovers, the ROPS should prevent a complete rollover (although it didn't on the Kubota shown on one of Marshall's links). That doesn't mean the tractor can't rear up 90° then roll to the side and it sure doesn't mean the operator won't get injured or killed.
I would think an implement (especially a long one such as a rotary cutter) would reduce the possiblity of a rear rollover.

Of course, I would think most rear rollovers occur when there is no implement rigged to the 3PH.

In one of the links, "Tractor Overturn Hazards", the author makes the following statement:
It is also possible to flip a tractor rearward when the load is properly hitched to the drawbar. This may happen when several factors occur. If the tractor is headed up an incline at too fast a speed and the load, such as a large log, suddenly digs into the ground, the rearward pull may be so quick and strong that the momentum generated by the rearward lift may result in a rear overturn."

He just gives one example. Anytime one is towing a load hooked to the drawbar and that load abruptly stops (log digging in), there would be a potential for a rollover if the momentum of the tractor is excessive (our TBN Engineers can do the math).

Another, more serious (IMHO) concern is those of us with Foldable ROPS who do not rig the ROPS in the proper position when using their tractors. I've seen a number of pictures on TBN of this very thing. Although the tractors were parked (the operator taking the "action" picture), it was pretty obivious the ROPS weren't being used. I expect to see deaths and injuries trending upward due to this misuse of the ROPS. I also expect we'll ultimately see foldable ROPS being eliminated or have some kind of safety switch installed to prevent use of the tractor when it is not properly set up.

 

[IslandTractor]

The flex links on my hogs offer an amazing 3" maybee 4" of flex. Eventually they do lock up metal to metal. Soundguy

You are correct and therefore a bush hog type cutter will act as a brake on rear roll over. There might be a bit more excitement than with a box blade but ultimately it would inhibit the rollover just as effectively. Which, by the way, is a good thing as that is the implement I carry around on the back of my tractor.

 

[RoyJackson]

I am throwing this into the discussion. A tractor with its rear wheels frozen to the ground could in theory backflip when starting out in forward in low gear. I heard about this years ago and I always start my tractor in reverse in the Winter "just in case". Jay

I was probably the first one to post this on TBN a few years back. I got it from one of the linked safety sites way back when...
The incident occurred in Nebraska. The operator had left the tractor in a field. This was a full sized utility machine, not a CUT. The rear wheels were frozen to the ground and when the machine was placed in gear, the tractor pivoted around the rear axle.
I'm guessing (years later) the clutch was released too quickly.

BTW, Jay, I also reverse my tractor initially if it's left out overnight in freezing weather.

 

[mars1952]

You are correct and therefore a bush hog type cutter will act as a brake on rear roll over. There might be a bit more excitement than with a box blade but ultimately it would inhibit the rollover just as effectively. Which, by the way, is a good thing as that is the implement I carry around on the back of my tractor.

Hi: Go back and read my first post. In my near rollover the linkage on the JD MX5 Rotary Cutter folded up like noodles. My ROPS would have stopped a complete rollover but the if the tractor hadn't had a ROPS the tractor could have rolled back on the cutter and I could have been sandwiched between the cutter and the tractor.

This point has been made several times in the thread. The linkage of the 3PH implement has to be strong enough to support the tractor after it passes the point of no return. If the linkage on the implement is not strong enough to hold up the tractor it just becomes something hard for you to land on or jab you through your ROPS.

There may be rotary cutters out there that are strong enough to prevent a rear rollover but most are not strong enough. Also I can picture a weak box blade folding up beneath a heavy tractor. (I have seen box blades that folded up during normal use).

Everyone that is following this thread, please follow the links and read them. Keep in mine that there is contradictory evidence presented and just because it is posted on the internet it doesn't mean that it is the absolute truth. As far as I can tell there doesn't seem to be a definitive way to prevent rear or side rollover just ways to lessen the possibility.

Marshall

 

[texasjohn]

Yep... lots of real facts and images and links to demonmstrations in this thread... we all need to read ALL the posts, consider ALL the worse-case situations and be as safe as we can be ALL the time. I'm really liking the fact-based tone of this thread...let's keep it that way

 

[Soundguy]

Hmm..I'd like to see a pic of the mx5.. does it not have rigid connections to support the a-frame? Also.. with a long implement on back. the tractor should not be able to reach a very high angle ( fronts off the ground ).. thus the implement doesn't have to suppor the weight of the tractor yet.. just resist traction forces... IE a 5' long mower ou the back should bottom out with the tractor at less than breakover point..

You bring up lots of 'ifs' if this.. if that. well sure.. IF you cahinn your tractor to an imovable object, and IF you have a wimpy implement on back, and IF you have no rops, then you will PROBABLY be mashed between that nice falt implement and your tractor IF you roll her over backwards. That's not a failure of anything but the operator... IMHO.. common sense has to come into play at some time.. there is no 100% effective operator protection system that is going to save a careless user from himself... However.. if peopl ekeep harping on how unsafe all these tractors are instead of taking a small amount of personal responsibility.... then eventually there will be so many product liability lawsuits that the gov't will step in and pass more ridiculess consumer protection laws that eventually you will have to have the equivalent of a combat trained jet fighter pilot's license, and 5000 hour of simulator time in order to buy a tractor.. and of course.. the tractor will be sportingan op platform that has this 3' thick hardened alloy steel ball with doors that look like belong on a bank vault.. inside there will be a 20 pt harness and 100% of the interior will be covered with air bags. there will have to be an emergency life support system and backup.. and a gps tracker with 100% full time security monitoring in case the loose transponder signal with you.. there may have to be an escape ejection system with HD parachute in case the operator drives it off a cliff... or a fire supression system.. so that of course means a wagon or tanker of foam or water that will have to be pulled along behind the tractor at all times or the starter interlock won't function. Still... there will need to be a computer controlled collision avoidance and skid system. / stability system. so incase a tire does spin.. the computer takes over and drive you out of the 'hazard' you might have been trying to plow.

All said and done.. the tractor will probably have to be built individualy on contract.. AFTER payment of the US 5.6$ million dollar deposit. which means.. no tractors..

Lets use some common sense and take some personal responsibility guys.

I do feel bad for the guy that gets crushed while skiding a huge 990# 10' long oak tree log with his 8n that has the chain attached to the 3pt rocker
and is moving it thru soft rocky soil and the tractor flips over and crushes him. I fell bad for him.. I also feel it was 100% his fault... still bad though..

Soundguy
Soundguy

Hi: Go back and read my first post. In my near rollover the linkage on the JD MX5 Rotary Cutter folded up like noodles. My ROPS would have stopped a complete rollover but the if the tractor hadn't had a ROPS the tractor could have rolled back on the cutter and I could have been sandwiched between the cutter and the tractor.

This point has been made several times in the thread. The linkage of the 3PH implement has to be strong enough to support the tractor after it passes the point of no return. If the linkage on the implement is not strong enough to hold up the tractor it just becomes something hard for you to land on or jab you through your ROPS.

There may be rotary cutters out there that are strong enough to prevent a rear rollover but most are not strong enough. Also I can picture a weak box blade folding up beneath a heavy tractor. (I have seen box blades that folded up during normal use).

Everyone that is following this thread, please follow the links and read them. Keep in mine that there is contradictory evidence presented and just because it is posted on the internet it doesn't mean that it is the absolute truth. As far as I can tell there doesn't seem to be a definitive way to prevent rear or side rollover just ways to lessen the possibility.

Marshall

 

[SPYDERLK]

- - Ever had a situation where you dont know exactly what is wrong, but you know its not right. Figure 5 in the Tractor Overturn Hazards link in post 18 presents just such a situation for me. The "angle of pull" is a puzzler. I can discern neither its intended meaning nor its true meaning. One would expect to be able to extrapolate and predict something from the geometry and the change in this angle with difference in chain length. So; 1) if the chain is // to the surface and long, the depicted angle of pull would be small, and 2) if the chain is very short the angle would be large - approaching 90. Is one to conclude something? Would it be that having a high angle is bad? Well, not in terms of safety. This imaginary line is not pulling down on the drawbar. Also, as soon as the tractor squats the short chain will be angled upward going to the load and subtract from weight on the wheels. This would detract from the capability to pull and eliminate rear rollback potential. - Would it be that a low angle is good? Well, yes in terms of actually being able to apply good sustained force while the tractor squats and rolls back and the drawbar moderates the roll as designed, but NO in terms of safety compared to the high angle. You cant actually do any real pulling at the high angle, so youre totally safe while being totally frustrated. What it comes down to for me is that the author has drawn an imaginary line between 2 points that he just couldnt resist connecting, but which have no meaning in the safety realm and certainly do not establish a pull angle. Other than this, and all reference to it, the authors description tells the physics to the same good effect as we in this thread, converged from 3 perspectives to the same conclusion. Maybe one of you can figure out what value hes conveying with that line. I sure cant.

As to the bushog value against rollover - Even tho they have the top flex link, or sometimes a chain that would thwart application of compressive forces entirely, you still get earlyearly warning on inclines and a good rollback pause from that way back tailwheel touching. Gently lets you know its time to start correcting a mistake. Trouble with using any implement as an actual wheelie bar on an incline is that the reference frame is already tipped critically wrt gravity, and the added free upward travel of the 3PH is likely to be too much to allow a stop of the rollback by the implement once the operator has missed his chance.
larry