Tires The last word on flipping tires.

[Mace Canute]

Wider front axle increases stability when you use your tractor on very steep side hills,

No it doesn't. The tractor's stability is totally dependent on the rear fixed axle. The front axle is at the same relative angle to the tractor as it is on level ground. The front axle oscillation stop doesn't come into play until the tractor has gone a considerable distance over. If you are on a smooth but steep side hill and the rear uphill tire lifts off the ground, you are going over...the rear track width is as wide as or wider than the front and since it wasn't enough to prevent the back from going over, the front definitely won't prevent the roll over, especially seeings as how the tractor has gone over a considerable extra distance.

and going over bumps at speed, but its not nearly as important as the rear. If you start to roll, the oscillation stop on the front axle will only catch you if you were barely going to roll. It won't stop a good bump induced roll or if the hill is just too steep for the rear tire spacing.

Exactly right! There may exist a certain set of circumstances where the oscillation stop on the front axle will prevent a roll over, but those circumstances would be very rare and if the stop prevented a roll over, you are definitely operating with a zero safety factor and well into the danger zone. Hitting a bump with the uphill rear tire or dropping the downhill rear tire into a hole introduces a set of unknown factors into the circumstances and the tractor may or may not go over...but whatever it does, I would bet my own money that the front track width would have nothing to do with it. Relying on an increase of a handful of inches in front wheel track width to save you from a roll over is just plain foolhardy and thinking that it increases the tractors stability is just wishful thinking.

Safety does NOT depend on wishful thinking!

 

[slowzuki]

Yes it does. The wider front axle causes the bumps on the uphill side to exert a smaller side thrust on the front end and can withstand a harder fetch up from a sideways slide before tucking under and rotating on the pivot.

This is wide highway row mowers have duals on front or very wide spacing. Just parking on a tilt table, no it doesn't matter much, but when moving it does.

No it doesn't. The tractor's stability is totally dependent on the rear fixed axle. The front axle is at the same relative angle to the tractor as it is on level ground. The front axle oscillation stop doesn't come into play until the tractor has gone a considerable distance over. If you are on a smooth but steep side hill and the rear uphill tire lifts off the ground, you are going over...the rear track width is as wide as or wider than the front and since it wasn't enough to prevent the back from going over, the front definitely won't prevent the roll over, especially seeings as how the tractor has gone over a considerable extra distance.

Exactly right! There may exist a certain set of circumstances where the oscillation stop on the front axle will prevent a roll over, but those circumstances would be very rare and if the stop prevented a roll over, you are definitely operating with a zero safety factor and well into the danger zone. Hitting a bump with the uphill rear tire or dropping the downhill rear tire into a hole introduces a set of unknown factors into the circumstances and the tractor may or may not go over...but whatever it does, I would bet my own money that the front track width would have nothing to do with it. Relying on an increase of a handful of inches in front wheel track width to save you from a roll over is just plain foolhardy and thinking that it increases the tractors stability is just wishful thinking.

Safety does NOT depend on wishful thinking!

 

[Reg]

Yeah, I think that "tuck under" might be where a wide front axle could save you.

ONE of the reflexes that I most fear on side/downhills is to try and turn up the slope if/when things get out of hand - the "tuck under" roll over.

Tricycle front ends went out for some other reasons too, but I don't think stability was one of their strong points.

 

[davygp38]

Yeah, I think that "tuck under" might be where a wide front axle could save you.

ONE of the reflexes that I most fear on side/downhills is to try and turn up the slope if/when things get out of hand - the "tuck under" roll over.

Tricycle front ends went out for some other reasons too, but I don't think stability was one of their strong points.

Since I don't have much in the way of a formal education, I tend to use other means to make some decisions, and one of the simplest is to take a look at different set ups, and how other people do things. I think you are dead on about the highway mowers. I figure, that whoever is in charge at the highway department, didn't just wake up one day, and decide to just go with a wider wheel track. I'm guessing that at some point, some egg head with a slide rule got a call about whether a wider track would be more stable. Obviously I can't throw out the old (x to the y squared= this that or the other,) but I feel that since most mower operations use a very wide track, there might be something to it. Now in this thread, almost everybody who has chimed in agrees that a wider rear tire set up is the best way to go. Now at the risk of sounding like a simpleton, why wouldn't a wider front end be just as big of a help? Remember the whole point of the thread, was to answer weather a wider front would help stability. My point is this. If my front wheels are a certain distance apart, and whether the Axel pivots or not, won't adding width make the machine more stable?

 

[Arky217]

OK, I am going to toss out a speculative theory that by flipping the tire on a dished rim that you dont put any extra stress on the axle. You simple transfer the stress in opposite directions. The rim centerline location is still bolted at the same spot. So when the dish is set to inside direction (narrowest)the stress on the axle is wanting to push the axle end down whereas when dished to the outside (widest) the stress would want to push the axle tip up. The same amount of force is on the axle and bearings, just pushing it in the opposite direction. The amount of steering load increases due to the longer leverage distance between the tires so you would get harder steering and likely a bit more wear on the steering knuckles. As for not worth it on the front due to pivot, folks claiming that have likely not noticed that the axle hits the frame way before the tractor would reach a roll over point, so widening the front stance helps to prevent tip over just as much as widening the back.
Please one of you engineering folks prove me wrong with some actual computations or CAD model not opinions.

I don't know how the front wheel bearings on a Kubota L4400 are set up, but on a vehicle that has a bearing setup typical of many past vehicles (a large inboard bearing and a smaller outboard bearing), changing the plane of the wheel thrust on the bearings from it's design point to further outboard can have undesirable consequences.

Real life case in point:

Years ago, I was traveling in a typical 2 ton truck (8.25x20 dual tires on the rear), when I had a blowout on one of the rear tires.
I didn't have a spare, but I decided to continue on my journey anyway after removing the wheel with the blown tire.

Before continuing, I considered whether to mount the remaining one wheel inboard or outboard. Well, I thought outboard would give me more stability (I didn't give a thought about the wheel bearings).

Turns out this was a BIG mistake. Within a couple of hundred miles, the smaller outboard bearing seized up to the point that it also ruined the axle.

Although the attachment plane of the wheel was in the same position, the thrust plane (from having only the outboard wheel mounted) moved further outboard and caused most of the weight to be transmitted to the smaller outboard bearing and comparatively very little to the larger inboard bearing, thus the outboard bearing quickly became overstressed and failed.

 

[dcyrilc]

Now at the risk of sounding like a simpleton, why wouldn't a wider front end be just as big of a help? Remember the whole point of the thread, was to answer weather a wider front would help stability. My point is this. If my front wheels are a certain distance apart, and whether the Axel pivots or not, won't adding width make the machine more stable?

The technical answer would be yes it adds stability. In a real world situation though, the answer in no. Here's the reason. The amount of stability is negligable, and on a side slope (or sometimes in a turn) where tipping is an issue, the amount of added stability is not enough to stop the tractor from rolling once it has started to tip and the momentum of the weight is already shifted past the edge of the rear tire (solid axle).

Picture the tractor sitting on a tilt table. Begin tilting the tractor to the side. Once the Center of Gravity of the tractor gets past the edge of the rear tire the tractor will begin to tip (roll). At this point, the COG is also already past the edge of the front tire as well. By the time the tractor has tipped far enough to hit the stop on the front axle, the COG will be so far past the edge of the tire that there is no way it is going to stop the tractor from tipping over. If the front axle was extended to a wide enough position, there is a point where it may have a chance of stopping the roll, but that point is way past where rotating a dished rim is going to have any effect.

Does this help at all?

 

[slowzuki]

No actually is does help in real life. Unlike the tilt table, in real life, tractors slide sideways and fetch up when operating on slopes. If the front tires aren't wide enough, they tuck under, lifting the front end, making the load (moment is the correct term) the rear tires have to resist much greater leading to roll over.

 

[dennis52]

No actually is does help in real life. Unlike the tilt table, in real life, tractors slide sideways and fetch up when operating on slopes. If the front tires aren't wide enough, they tuck under, lifting the front end, making the load (moment is the correct term) the rear tires have to resist much greater leading to roll over.

You guys both sound like you know your business!

With regard to impending side rollovers and fetch up, can you advise the effect of
1. Fully loading tyres (above and below centre of gravity)
2. Only loading tyres to axle height (below centre of gravity)
3. Not loading tyres but carrying equivalent weight very low with loader and bucket on front and 700lb brush hog on rear.

 

[slowzuki]

1. Loaded tires usually help, they are generally loaded to the top of the rim, and would slightly lower the COG.
2. Less loading of the tires could lead to more sloshing, and up here calcium is used so it is always over the rim. I don't have experience.
3. Always carry loads low when on a hill, in my experience, loads in the front loader are tough to get low enough to help, once the centre of a loaded bucket is level with the axle pivot, its isn't helping. Higher makes it worse.
Rear ballast helps, if is low and isn't swinging.

 

[RoyJackson]

So far, we're up to 40 or so "Last Words..." in this thread.

I flipped mine on my old 790. Can't say with certainty it helped much (only gained a couple inches in track) but it did feel better, even with that pivoting axle.
If you're already on a slope, the axle has (likely) already pivoted as far as it's going to go, once it's hit it's stops (taking that out of the equation). That wider stance may give you a bit more stability.
As far as the wheel bearings wearing faster...probably...and more so if your front wheel are deeply dished (meaning a much wider track when reversed), the wear would be quicker. Then one has to determine if that relatively slight increase in stability is worth the potentially early replacement of those bearings.

However, I've not reversed the fronts on my 4400 and I don't intend to. I've got more weight in the rears (much larger tires) and just don't see much need for it.