Tractor "bouncing" ?

[timbrr]

Howdy folks. I'm trying to research and understand an issue I'm having with my Kubota MX5100 HST, but don't seem to be using the right search terms.

This is the first tractor I've owned, and I've only clocked up ~220 hours so far. Most of that has been spent in 4WD mode digging and moving dirt -- mainly (what was formerly beach) sand. As I have become more proficient I have been transporting larger and larger amounts in the (4-in-1) bucket. I have a 500kg counterweight on the 3-point hitch. All tyres are industrial R4s. Fronts are inflated to 32psi (with max rated at 45), whilst rears are inflated to 15psi (with max rated at 20).

When I transit from A-B over lightly-vegetated -- but otherwise well-compacted -- sandy soil, the initial few runs will be as expected. The tractor will react to roughness in the underlying terrain in a predictable fashion. Sometimes, however, I end up going over the same A-B track several times, dozens of times, even hundreds of times. In short order my tractor experiences what I can only really describe as "bouncing".

It feels like the whole tractor just starts bouncing up and down. The "severity" of the bouncing increases over time/distance as I traverse the A-B track. In mild cases this is merely annoying. In severe cases the bouncing is so extreme that the springs on my seat are unable to compensate, and I experience a spine-jarring jolt as the seat grounds out. Not fun.

Going forward results in more bouncing than going backward. Full buckets result in more bouncing than partially-full buckets. That said, I have experienced bouncing even going backward with an empty bucket (neither as frequently or severely, but it still happens). Bouncing is usually worse the faster I go, but neither consistently so, nor within a fixed speed range. Sometimes going 'fast' actually prevents bouncing. Going really slowly (~5km/h or less) reliably prevents bouncing, but given the distances I need to travel, such low speeds are undesirable. The gears are in 'M' during transits.

Natural ground deteriorates pretty quickly when subjected to loader operations. It gets dusty/powdery quite quickly. Back-dragging the track with the loader bucket will visibly smooth out the track, but bouncing resumes almost immediately (within 1-3 transits). Dumping and spreading sand over the path helps for a while longer.

Searching the forums for "bounce" or "bouncing" returns zero results.

Can anyone suggest keywords that describe the phenomenon that I am experience which will help me research the matter further?

Cheers!

 

[dodge man]

Is the bouncing front to back, or just straight up and down. When I don’t have any or enough weight on the back the tractor will rock front to back pretty bad. I’d try playing with tire pressure. My initial reaction is your front tire pressure is to high but I’m not sure. It might just be normal also, tractors don’t have a suspension so about all you can do is slow down.

 

[k0ua]

You may or may not have noticed that tractors have no suspension components. NONE. When traversing rough terrain, you may have noticed this "bouncing " phenomenon. The solution to this is to slow the he77 down. Especially in the rough parts and especially when heavily loaded. Low and slow for safety, and in your case comfort too.

 

[Ford850]

I've noticed when hauling heavy bucket loads over the same path, the bouncing gets worse. I've figured it out, at least for me. First, the 'path' I choose gradually gets smoothed out, flattening the many small bumps and rough ground. That leaves a smooth path but accentuates the slightly larger humps and whoopty-doos. Second, once I get that smooth path I gradually travel at a higher speed compared to the first few trips over it, since the many small bumps are gone and I feel safe. If I can drive the path in mid range, 3rd gear, then I should be able to bump up to mid 4th and save some time, right? Third, I find myself loading larger and larger buckets full after the first couple trips. If 'full' worked, then 'fuller' must be better since it will save me trips, right?
Add those three things and by trip 10 I'm nearly ejected off my seat in some spots before my brain kicks in and I slow down and reduce my loads. My suggestion... Slow down and enjoy the ride.

 

[k0ua]

If you insist on operating at the ground speed that causes you discomfort, you can check on increasing the stiffness of your suspension seat's adjustment, or you can lose some weight. Not on the tractor or the load but your weight. I don't know if you are skinny or fat, but a fat man is going to bottom out a seat's suspension travel a lot faster than a skinny man. I know this firsthand, being in the "fatboy" category. An alternative is to replace the OEM seat with an air ride suspension seat. They are sold by several aftermarket vendors, and can be more comfortable than the OEM seat in these conditions. Or you can save the money and reduce your ground speed.

 

[timbrr]

Is the bouncing front to back, or just straight up and down. When I don’t have any or enough weight on the back the tractor will rock front to back pretty bad. I’d try playing with tire pressure.

I'm not sure what front-to-back bouncing would even feel like. Rocking? If that's the case, then no, the tractor doesn't rock froward and backward. Just up and down.

I've entertained the thought that I might not have a big enough counterweight on the 3PH, but given that I even bounce with an empty bucket, I'm not sure that line of reasoning is getting to the heart of the "problem".

 

[k0ua]

Slow down and enjoy the ride.

Best advice of the day..

 

[finn1]

Any object has what, in engineering terms, is called a mass-elastic system and a resultany natural frequency that it “vibrates” at. The mass elastic system can be mathematically modeled given the stiffness, mass and spring rates of the components and assemblies, and enough computational powers. Wheelbase is one of the factors too.

What’s happening is that your machine is compacting the earth, causing “ripples” that excite the natural frequency of your tires, and vehicle mass.

You can change the response by speeding up, slowing down, or changing the air pressure or stiffness of your tires so you aren’t exciting the tractor at the natural frequency of its Nass elastic system.

Cars sometimes, in the past, had what was referred to in technical circles as “California freeway hop”. The story goes that the expansion joints in California freeway pavement were spaced slightly different than most other typical highways. That longer spacing set up many cars structures and suspensions to go into resonance when crossing the expansion joints at the speed limit, resulting in an uncomfortable ride.

Designing cars to a higher mass-elastic stiffness keeps the resonance to a minimum.

This phenomenon was part of the Mechanical Engineering curriculum fifty years ago when I was a student.

 

[Jchonline]

I expect this is due to small indentations created in the dirt/sand as you repeatedly travel over the same path. Sand is very impressionable as you know. The bouncing is accentuated because you have an unbalanced load (not unsafely unbalanced) but from a physics perspective you have more weight out front than out back.

I have also operated a Mini-EX and until I got used to the controls it would rock really bad when I tried to go forward with by actuating both tracks. Same idea. Some imbalance of weight coupled with a very small uneven motion that starts it all.

Oh try it in another vehicle on the same path to see if you notice. Like a car or truck.

Other than slowing down, no way I can think of to fix. Balance the load and slow down to minimize it. Find better dirt that doesnt keep reforming ;(

 

[k0ua]

Now we could get all "technical" on you, and talk about unsprung weight and torque arms, and you could perform your own experiment by taking off the loader and removing the ballast on the 3 point hitch and traversing the same exact ground at the same exact ground speed and you will notice that the bare tractor has much less "bouncing" with those items removed. But none of this offers you the practical solution of traversing the same exact ground at a lower ground speed does. Yeah you can try to adjust the OEM seat or even buy that air ride seat, neither of which will reduce the bouncing, but might prevent the spine jarring bottoming out experience, but the root problem remains. You are simply going too fast for the terrain.

 

[timbrr]

When traversing rough terrain, you may have noticed this "bouncing" phenomenon.

I'd fully expect to be bouncing on "rough" terrain. But that's not the case I'm describing, The bouncing occurs on regular terrain. On essentially flat ground (albeit with small amounts of some different types of grasses growing on it). No slopes, no rocks, no ruts.

I can even add sand and build up the track by 10cm or so, smooth it out with the bucket, and the bouncing will return.

A track that can be comfortably traversed at a given speed with a given load with no bouncing whatsoever, eventually can no longer be traversed at the same speed with the same load without bouncing.

 

[jeff9366]

Just wondered what everyone thinks of this new product by W. R. Long. The name is a bit deceptive as it's not something intended to directly improve the "ride" of your tractor, but it dampens the movements of the FEL as you traverse over (uneven) ground. The end result I suppose is that it could reduce the jerky movements of the tractor as you drive it over rough terrain, and help it ride a bit smoother. Their main selling point though seems to be that it reduces the wear and tear on the loader's mechanical joints, and maybe reduces the metal fatigue as well.

I think the theory behind it is good, but it would be nice if they could show a side by side comparison of two identical tractors, one with the system and one without the system, driving over the same terrain. I'm not thinking of buying one, mind you, but the hydraulic dampening technique just peaks my interest a bit. The suggested retail price of the CR10 is $425 and the suggested retail price of the CR20 is $475, if you're interested. :thumbsup:

W.R. Long, Inc. | Tarboro, NC

Kubota dealer installed the Long CR10 on my L3560 with LA805 FEL. Works as advertised. With moderate loads of brush on Debris Forks damping actions eliminate material falling off during transit. Productivity is enhanced.

One hydraulic line had to cross the right loader arm in my ((early)) installation.

With CR10 working, bucket does not pound, burdened or unburdened.

Oak section guesstimate 1,200 to 1,400 pounds. FEL (LA805) lift capacity 1,700+ pounds. I cut large diameter Oak loads to fit in the bucket, near to the tractor, rather than on the forks, where leverage works against stability. Three Point Hitch counterbalance 900 pounds. Much less transient load stress on the tractor with Long's "Comfort Ride" cushion-accumulator installed.

Kubota factory "Shockless Ride" option is available on the Kubota M5660 with LA1154 loader.

Kubota should offer Shockless Ride option on the Grand L series. The proverbial cherry atop whipped cream.

 

[Hay Dude]

When I Road my hay tractors, they will ride perfectly up to about 22MPH, but increase throttle and try to go the full 24.5MPH and they will porpoise wildly front to back. I did find increasing tire pressure helps, but then ride quality sucks in the fields. These 2 tractors have soft ride option on the loaders, and one has a front axle suspension. However, the front axle suspension doesn’t help with the porpoising. It does help in bumpy fields.

My larger tractor, which has a 34MPH road speed, has a front axle and cab suspension, which helps tremendously. It does not bounce front to back.

I think tire brand/quality might also be a factor.

 

[timbrr]

If you insist on operating at the ground speed that causes you discomfort...

My personal comfort is not really what I'm worried about. The MX5100 has Mechanical Front Wheel Drive, so when I'm in 4WD mode the front and back are mechanically coupled. Since the bouncing accentuates the HST/drive-train noise I am mainly concerned about wear and tear on some sort of (obscure) HST/drive-train-related component.

 

[timbrr]

I've noticed when hauling heavy bucket loads over the same path, the bouncing gets worse. I've figured it out, at least for me. First, the 'path' I choose gradually gets smoothed out, flattening the many small bumps and rough ground. That leaves a smooth path but accentuates the slightly larger humps and whoopty-doos. Second, once I get that smooth path I gradually travel at a higher speed compared to the first few trips over it, since the many small bumps are gone and I feel safe.

A pretty accurate description of what happens with me up until this point...

If I can drive the path in mid range, 3rd gear, then I should be able to bump up to mid 4th and save some time, right? Third, I find myself loading larger and larger buckets full after the first couple trips. If 'full' worked, then 'fuller' must be better since it will save me trips, right?

...but I don't go up a gear, or increase the size of loads. They remain constant.

My suggestion... Slow down and enjoy the ride.

Yes, that does stop the bouncing, but it may not be the only solution to the problem.

 

[LouNY]

As others have said the best thing is to slow down.
The various "soft ride" loader additions are designed to dampen the loader oscillations and will do so.
At the speeds you are traveling I'm surprised that you are in 4wd,
one item to be aware of is with the tractor bouncing and loading and unloading the tires is that every cycle will change the
loaded radius of your tires which in turn will affect your front - rear tire balance.
Any tractor with a loader will bounce or porpoise more then the same tractor without a loader, just removing the loader bucket when not needed also reduces the bouncing and stress on the front axle.
The only way to reduce the stress on the tractor is to slow down.
The paved road that we use the most with the tractors has gotten so rough in the tractors that we can't use the highest gears for road hauling, we have to drop down one or two gears and throttle down on the paved road.
The town graded a dirt road the other day and I could actually run faster on that then the paved road for a few days.

 

[timbrr]

Any object has what, in engineering terms, is called a mass-elastic system and a resultany natural frequency that it ç*ºibrates at. The mass elastic system can be mathematically modeled given the stiffness, mass and spring rates of the components and assemblies, and enough computational powers. Wheelbase is one of the factors too.

What痴 happening is that your machine is compacting the earth, causing 途ipples that excite the natural frequency of your tires, and vehicle mass.

Kind of like resonant frequencies in music? Constructive interference then increases the amplitude of motion?

You can change the response by speeding up, slowing down, or changing the air pressure or stiffness of your tires so you aren't exciting the tractor at the natural frequency of its Nass elastic system.

Modifying components of the system (e.g. tyre pressure) would likely alter, rather than eliminate the existence of, such frequency -- correct? If so, then the symptoms would disappear whist the tractor and the track were out of sync. Over time, the track would be remoulded by the new frequency and the symptoms would return, I assume.

If that's the case, and given that most of the tracks are temporary in nature, changing air pressure probably wouldn't be practical as it wouldn't (permanently) solve the problem. Changing transit speed from trip to trip likely would help though. I have noticed that often just changing speed (up or down) subdues the severity of (i.e. 'dampens') the bouncing.

Cars sometimes, in the past, had what was referred to in technical circles as California freeway hop? The story goes that the expansion joints in California freeway pavement were spaced slightly different than most other typical highways. That longer spacing set up many cars structures and suspensions to go into resonance when crossing the expansion joints at the speed limit, resulting in an uncomfortable ride.

Designing cars to a higher mass-elastic stiffness keeps the resonance to a minimum.

So, apart from increasing tyre pressure, is there any way to increase the "stiffness" of a tractor?

 

[ruffdog]

timbrr....I have neighbors that have big end-loaders and also road crews use them, and they will get bouncing on a SMOOTH road surface. I have a feeling that off-road tires are not as round and consistent thickness as on-road tires. If they all start acting in unison, then you get bouncing. Just like them, you just have to slow up, get through it, and try to change the conditions like you have been. The bouncing you describe does seem to happen more on smooth surfaces more.

 

[orezok]

This may not be relevant, but with my B7800, it has a tendency to porpoise when carrying loads in 4 wheel drive. If I switch to 2 wheel, the motion greatly decreases. I guess that the front and rear drives are at a little different road speed causing the rocking as the drive train loads up and then suddenly releases as one axle loses traction.

 

[Gary Fowler]

This may not be relevant, but with my B7800, it has a tendency to porpoise when carrying loads in 4 wheel drive. If I switch to 2 wheel, the motion greatly decreases. I guess that the front and rear drives are at a little different road speed causing the rocking as the drive train loads up and then suddenly releases as one axle loses traction.

I suspect this is exactly what is happening to the sand, the front wheels turn just a little faster so they tend to mound up the loose sand a bit with each pass and eventually this starts the harmonic "loping " so you end up bouncing up and down in the seat. Each time the tires run over the humps they react more and more so you end up with a big up and down, front to back hop. Back dragging to remove the humps results in a smooth ride for a couple trips till the front wheels throw up the humps again.

Try travelling in 2WD if it is safe to do so, ie, not hills to traverse where you might loose rear wheel traction.