Longer wheelbase = better stability?

[aggc]

I have systematically narrowed my choices for a new tractor down to the Kubota L3400, L3130, or New Holland TC33. I have unfortunately been cursed with an Illinois-influenced equilibrium that makes it difficult for me to mow on slopes. I always feel like I am tipping over if I'm not on level ground. Strange but true. At any rate, the L3130 has a wheelbase about 8-10" longer than the L3400 and TC33 and about 700 pounds heavier. My question is this: does the longer wheelbase and increased weight translate into a more stable tractor? Would it be of genuine benefit on uneven ground?

 

[texbaylea]

I have systematically narrowed my choices for a new tractor down to the Kubota L3400, L3130, or New Holland TC33. I have unfortunately been cursed with an Illinois-influenced equilibrium that makes it difficult for me to mow on slopes. I always feel like I am tipping over if I'm not on level ground. Strange but true. At any rate, the L3130 has a wheelbase about 8-10" longer than the L3400 and TC33 and about 700 pounds heavier. My question is this: does the longer wheelbase and increased weight translate into a more stable tractor? Would it be of genuine benefit on uneven ground?

I feel weight and width of wheelbase are the important factors. I don't have any significant grades except in the roadside ditch in front which means I mow along the slope or not at all. There are a couple of places where I estimate the slope approaches 20*. I am apprehensive when mowing these but with filled R4s my L3130 has never offered to tip. I have made sure that there are no holes along my route. Where there are I leave for the county to mow however infrequently. They use batwing mowers so the tractor stays in the bottom of the ditch.

Vernon

 

[Bob_Skurka]

It is difficult to tip over a Jeep Wranger. They have a short but wide wheelbase. I think width is going to be more important than length.

As for weight, that is a far more difficult question to answer. If the weight is high, then your center of gravity is high and you can tip. If your weight is low, then your center of gravity is low and tipping over would be much more difficult. I think simply looking at raw weight could be very misleading. Sailboats have one point on their sail that is called the center of effort. In theory if you push on that point you can roll the boat. The reality is that wind blows below that point and above that point so there is some balance. Tipping a tractor is going to be similar. Load the wheels with fluid and most of the weight will be at or below the axle, which is good for stability. Use wheel weights and 50% of the weight will be below the axle line while 50% will be above it. Add a cab to the tractor and you move the weight higher. Lift the loader bucket 18" off the ground and your also lifted the weight of the arms, buckets, etc and raised your center of gravity.

 

[WayneW]

Well, to use the Jeep comparison again.

The old CJ5 had a 84" wheelbase.
Was replaced by the CJ7 because of stability issues. Wheelbase - 93.5"

The Wranglers have a 93.4" wheelbase. About 9.5" longer than the CJ5. Is wider than the CJ7.

In fact, the 2007 Wranglers are even wider (3.5") and longer than previous Wrangers.

Why? Stability. The government is cracking down on all SUVs due to rollovers. A jeep is NOT a stable vehicle. I've ridden in many over the years. They have gone from just plain scary (CJ5), to making me feel a little queezy in tight situations (Wrangler)

My point is simply that (obviously) wider, and yes, even longer makes for a more stable ride. One. less suseptable to rollover. In Mass. there is a lift height law derived by a formula.

Amount of lift= (track) X (wheelbase) / 2200.

The 2200 is a "safety factor", but notice that the wheelbase is given the same amount of "weight" in the formula as width. (track) It is that important.


As Bob pointed out, tractors have an advantage over trucks/SUVs. By loading tires you can put a greater percentage of the tractors' weight down low, near the axle. You can't realistally do that with a truck.

Though I do beleive that the weight issue uses the basic tractor dimensions, as a reference point. You are far better off when starting with better odds.

sorry for the long rant. But it's one of the few things here, that I actually know about. Been there...done that type of thing.

-best of luck

 

[SPYDERLK]

Quote: My question is this: does the longer wheelbase and increased weight translate into a more stable tractor? Would it be of genuine benefit on uneven ground?

YES. Both width of the back wheel stance and longer wheelbase add up to a more stable tractor. The longer wheelbase will be a little less maneuverable, but will pay you back by a less extreme shift of weight to the front when going down hill. Your stability comes from weight on, and width of the rear stance. This remains more consistent on a long wheelbase. Many CUTS are entirely too short and must be counterweighted carefully to keep them from standing on their nose with even light loader work.
Larry

 

[ovrszd]

Well, to use the Jeep comparison again.

The old CJ5 had a 84" wheelbase.
Was replaced by the CJ7 because of stability issues. Wheelbase - 93.5"

The Wranglers have a 93.4" wheelbase. About 9.5" longer than the CJ5. Is wider than the CJ7.

In fact, the 2007 Wranglers are even wider (3.5") and longer than previous Wrangers.

Why? Stability. The government is cracking down on all SUVs due to rollovers. A jeep is NOT a stable vehicle. I've ridden in many over the years. They have gone from just plain scary (CJ5), to making me feel a little queezy in tight situations (Wrangler)

My point is simply that (obviously) wider, and yes, even longer makes for a more stable ride. One. less suseptable to rollover. In Mass. there is a lift height law derived by a formula.

Amount of lift= (track) X (wheelbase) / 2200.

The 2200 is a "safety factor", but notice that the wheelbase is given the same amount of "weight" in the formula as width. (track) It is that important.


As Bob pointed out, tractors have an advantage over trucks/SUVs. By loading tires you can put a greater percentage of the tractors' weight down low, near the axle. You can't realistally do that with a truck.

Though I do beleive that the weight issue uses the basic tractor dimensions, as a reference point. You are far better off when starting with better odds.

sorry for the long rant. But it's one of the few things here, that I actually know about. Been there...done that type of thing.

-best of luck

Some very good theories. I don't think the length theory is as important in a tractor as it is in a road vehicle. Length comes into play on the road when a Deer runs in front of you, or there's suddenly an accident in front of you or you blow a tire, etc. We don't have those problems with a tractor so it's not quite so important as width.

Sure glad I don't live in Mass. Sounds like they can only lift a Jeep 2.5".

 

[Turbys_1700]

Long...Low...Wide...Weight...
They all play a signigficant aspect in side hill stability...
Guys up here in the NC mountains typically put low-profile tires on their tractors while also putting extensions on the rear wheels...
Widens the rear track and lowers the center-of-gravity...
Get the tractor that serves your pruposes best...
Then try it out prior to making any modifications to tires and the such...
Adjust as necessary...

 

[rbargeron]

My question is this: does the longer wheelbase and increased weight translate into a more stable tractor? Would it be of genuine benefit on uneven ground?

Tractor front axles are pivoted in the middle so the front wheels don't directly affect the "feel" of stability on slopes - it's mostly from the rear wheels. The WIDER the REAR WHEELS are mounted, the more stable the tractor is (and feels). As pointed out above, wheelbase length plays a role in higer-speed vehicles - but the differences in length in the tractors you are considering is much less of a factor. The most stable tractor is the one with the most width adjustent available at the rear wheels. Also, R4 rubber makes the tractor lower (lower CG = more stable).

Tractor stability is a much different situation than road-speed vehicles. The most common root cause of a tractor rollover is a sudden slope change at the rear axle - dropping one wheel into a hole, or running over rock or other upthrust at a rear wheel. The answer is less speed, and more overall tire width at the back. Liquid filling of rear tires also helps a lot - with liquid level at the top of the rim, the CG of the liquid is below the axle centerline. Take care, DickB

 

[WayneW]

SpyderLK makes another excellent point with many CUTs being too short.

Ive moved many rocks with my B7610 (shorter wheelbase than either the B7800 or L series) with BOTH rear tires off the ground! I pivited on the front tires in 4WD low.

This was on flat ground of course and not for long distances.
And yes, I had a 5' box blade with cement blocks for counterweight.

 

[azhfl56]

ok, think of this way. Remember the old fulcrum lever theory right? We all have used it. Ok, think of your wheels as the fulcrum and your tractor frame, (wheelbase) as the lever. A shorter tractor has less weight and leverage on the axles than does a longer tractor wheelbase. So, if the tractor is less inclined to move up or down along the axle plane it should be more stable because there will be less movement due to weight transfer from front to rear or vice versa. This will add to stability both in a slow moving vehicle and a faster moving vehicle. Width is also part of the stability, I don't think anyone questions that. However, length is also part of it. I tried to explain the length vs. stability using something we have all done before. I hope it makes as much sense to you guys as it does to me, or at least as much sense as I
intended. The longer the lever the more force you can put at the fulcrum. The shorter the lever the less force. Clear as mud right?

Regards,

Bryan

 

[rbargeron]

Your fulcrum analysis is exactly right. The length definitely defines what loads you can balance and obviously affects forward-to-back stabilty. But AGGC's original post said he was concerned about stabilty when mowing on slopes - feeling like he was tipping over when it wasn't level. Side-to-side stability isn't made better by length. In fact, only when there is enough angular difference between the front and rear axles to reach the front axle's pivot stop, does the front contribute to the "righting moment". The front axle may actually help prevent a roll, but if the wheel base is too long even that effect is reduced, especially if the total CG is high. Anyone old enough to remember the tricycle tractors knows how little the front contributed there. They were strictly flatland machines - although many found their way into the hills where they were involved in a lot of injuries.

 

[azhfl56]

I like your added analysis. However wouldn't a longer wheelbase lessen the effects of hitting a hole/ dropping into a hole while traversing a hill?

In short, if I were looking at a tractor and all things being equal, width etc. and one had a longer wheel base than the other and space weren't an issue, I would probably choose the longer wheelbase.

If the hills are that sever, then they should only be traversed head on, or to be totally safe, backward, never sideways.

The best way to mow hills is with a good Zero turn mower, or maybe an M1 Abrams fitted with a batwing!

Regards,

Bryan

 

[rbargeron]

.....wouldn't a longer wheelbase lessen the effects of hitting a hole/ dropping into a hole while traversing a hill?

I've been thinking about that and it might be just the opposite. I think the limit of the front axle's pivot range can be less with shorter wheelbase, hence the contribution from the front can be bigger sooner if the wheelbase is short. I'm not real sure what the design constraints are on front axle motion, but it would seem logical to try to have all wheels in contact with the ground as much of the time as possible. On uneven ground, the longer the wheelbase the more pivot angle would be needed to accomplish that. Conversely, if the wheelbase is shorter, the pivot can be more limited for better righting moment contribution. None of these factors operates in a vacuum - they interact with width, CG height, overall weight, likely attachment loads, yikes, makes me glad I'm only a nuclear engineer

 

[SPYDERLK]

Your fulcrum analysis is exactly right. The length definitely defines what loads you can balance and obviously affects forward-to-back stabilty. But AGGC's original post said he was concerned about stabilty when mowing on slopes - feeling like he was tipping over when it wasn't level. Side-to-side stability isn't made better by length. In fact, only when there is enough angular difference between the front and rear axles to reach the front axle's pivot stop, does the front contribute to the "righting moment". The front axle may actually help prevent a roll, but if the wheel base is too long even that effect is reduced, especially if the total CG is high. Anyone old enough to remember the tricycle tractors knows how little the front contributed there. They were strictly flatland machines - although many found their way into the hills where they were involved in a lot of injuries.

The short wheelbase unloads the rears too readily. That is the sole reason that the long wheelbase is more stable on slopes, however it is an inescapable reason. The four wheel tractor is no more stable than the tricycle because they are both tricycles until the 4 wheel reaches the limit of articulation on the fronts. Then you might get a second chance, but one of your rears is already in the air - - tip has started - the CG has risen. If theres lots of weight on the fronts youll tip early but probably stop with the rear wheel in the air when the front axle reaches its limit. With the longer tractor the weight does not shift to the fronts so much on downslopes. You can go down a steeper slope in 2wd w/o sliding. You can go on a steeper down diagonal or a pure side slope w/o tipping because the rears stay loaded better, especially with weight on a loader. The ordinary CUT wont even work on the slope that the longer tractor will unless it is accurately counterbalanced for the situation at hand - - then you turn or the slope changes and the long tractor reacts less. Finally, after the short tractor has had to retire to watch, the long tractor tips. It may not stop tipping like the short tractor did on considerably less slope. At this limit, beyond that which the short tractor can operate, the long tractor will operate, but with less forgiveness of error than the short one exhibited on a lesser slope.

Front to back stability improves side to side stability, but the higher limits permitted come at a cost of added criticality at the steeper tip point.
Larry

 

[WayneW]

Yes, excellent analysis with the fulcrum explaination. I've thought about this some, and came to the conclusion that a tractor is NOT the ideal machine for lifting heavy weight with a loader.

...off topic a bit, but.....

I've always been impressed by Bobcats and what they can do with such a small machine. BUT, notice where the lift arms of the loader are attached. In the rear, behind the rear tires. Due to reasons already explained here, it is designed differently than a tractor, more for heavy lifting with a small machine. It's almost as if the pressure applied to the lift arms create their our counterweight to the rear when lifting heavy loads.

But then again, it's tough to mow with a Bobcat.

It's all about compromises. Personally I'm thrilled to be able to move large amounts of dirt and rock with my B7610, AND mow the lawn, pick up leaves, level and snowblow the driveway.