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  #51  
Old 06-07-2006, 05:49 PM
mowtech mowtech is offline
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Quote:
Originally Posted by HK45Mark23
There is no pivoting axle on a Lastec, it is simply a tripod.

The stability comes from the fact that there are only 3 weight bearing wheels.

Again if you take a tripod and a 4 legged table or stool and put them on the same uneven surface you will immediately know which one is stable.

Again, if you have an uneven surface and one wheel is up in the air (even if only an inch) you have several hundred pounds suspended and that cantilevers to the diagonally opposed wheel and reduces the weight on that wheel.

Since the front wheels are casters and the drive and steering is being managed buy the rear wheels this becomes most important.

When two functions are being performed by on set of wheels they need to be in contact with full operational pressure at all times to perform the tasks of providing both drive force and steering force.

Once a caster pops off the ground and all of the weight it bares is now teetering on the wheel directly behind it and the one to its side then the drive wheel diagonally apposed to it will loose its ability to perform and a loose of traction will occur.

if this happens (and it does) on a hill then because you only have one wheel that is a drive wheel and one that is a caster that is in good contact with the ground then it is inevitable that it will spin out of control and go down the hill.

This is physics absolute. It has nothing to do with a pivoting axle because Lastec does not have a pivoting axle. It has to do with physics of weight shift and contact the patch friction coefficient.

The loss of contact and hence friction due to reduction of pressure when one wheel is in the air and all of its weight is pulling the diagonal wheel off the ground and it happens to be a drive wheel leaving only two wheels one drive and one caster in contact and the fact that a caster rotates and therefore allows the mower to spin out of control.

Once you have a mower that does not ever have weight shift like a tripod designed mower such as the Lastec then you have hill handling stability unparallel by any 4 wheeled mower.

I agree with what "Envy" has posted. A three legged table or three wheeled machine is absolutely not more stable than a three legged table or machine. Yes a four legged table will wobble on an uneven floor, but it still remains more resistant to being knocked over sideways. This is the true definition of stability. This is absolute physics. Please do not try to misinform people. I can and have taken three wheeled machines and compared them to four wheeled machines on a tilt table and the stability of the four wheeled machine is always better than a three wheeled machine. The three wheeled machine will tip over first every time. With a Z mower, as you go sideways on slopes, the steeper the slope, the less weight is carried on the up hill wheel/wheels. At some point this will get to the point where the up hill wheel looses traction and control is lost. The three wheeled machine will loose this up hill traction first because it is less stable. Now I admit and have stated the advantage of the three wheel design in other posts. You are correct that on an uneven surface that all three wheels will remain in contact with ground as long as the machine has not reached its point of instability due to its center of gravity moving out past a line connecting the two down hill wheels. This effect does not make the machine more stable, it just allows for better traction of both drive wheels in the case of uneven ground. Now all ground is uneven, so the three wheel design can and does improve control on side hills. But your example is not quite correct ("Daner" is correct), when a front castor is off the ground, the two drive tires still remain in contact and you still have traction and control. When a rear tire becomes unweighted, then you have an issue with possible loss of traction and control. Sure the Lastec "wings" may help prevent roll over, but as said before the issue is NOT stability. All Z are very stable on side-hills. Most, if not all need a slope in excess of 45 degrees, which is extremely steep to tip over. The issue is loss of traction and control. The Lastec may be better up to a point because of the three wheel design, but it is not immune to the issue of loss of traction and control.
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  #52  
Old 06-07-2006, 11:12 PM
Envy Lawn Service's Avatar
Envy Lawn Service Envy Lawn Service is offline
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Well, I hit in the middle, in some agreement with everyone.
But here is the bottom line...

In all cases, except traveling UPhill forward...

ALL 'stock' zero turns will LOOSE TRACTION long before reaching the rollover stability marker.

I think that this in a nutshell is what us end users are getting at. Stability is NOT the true issue. LACK of TRACTION 'IS'. This causes loss of control and makes the operator more vulnerable to injury by several means.

I would go out on a limb here and say most ZTR related personal injury situations BEGIN with loss of control due to LACK of TRACTION.

Yeah, I'm sure that frequintly somebody gets too close to the edge somewhere and has a rollover accident due to soil collapse, and I'm sure occasionally somebody gets too brave, drives up too steep a slope and panics when the front wheels lift, resulting in backwards rollover.

But in most cases, I'm sure loss of traction causes loss of control and the machine goes where it should not, resulting in a crash, a swim, or a rollover from bouncing, abrupt terrain or drop-off.
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  #53  
Old 06-08-2006, 10:33 AM
mowtech mowtech is offline
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Join Date: May 2005
Location: Midwest, USA
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Quote:
Originally Posted by Envy Lawn Service
Well, I hit in the middle, in some agreement with everyone.
But here is the bottom line...

In all cases, except traveling UPhill forward...

ALL 'stock' zero turns will LOOSE TRACTION long before reaching the rollover stability marker.

I think that this in a nutshell is what us end users are getting at. Stability is NOT the true issue. LACK of TRACTION 'IS'. This causes loss of control and makes the operator more vulnerable to injury by several means.

I would go out on a limb here and say most ZTR related personal injury situations BEGIN with loss of control due to LACK of TRACTION.

Yeah, I'm sure that frequintly somebody gets too close to the edge somewhere and has a rollover accident due to soil collapse, and I'm sure occasionally somebody gets too brave, drives up too steep a slope and panics when the front wheels lift, resulting in backwards rollover.

But in most cases, I'm sure loss of traction causes loss of control and the machine goes where it should not, resulting in a crash, a swim, or a rollover from bouncing, abrupt terrain or drop-off.
From the accidents I've personally investigated and am otherwise aware of I agree 100 per cent with "Envy".
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  #54  
Old 06-08-2006, 12:25 PM
JS Landscaping's Avatar
JS Landscaping JS Landscaping is offline
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Location: Orange County NY
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Another sad incident which happend just around the corner from me this past monday. Be careful out there guys. The mower in this incident was a Scag Turf Tigger, no Rops.

http://www.recordonline.com/search?N...S-doc-number=1




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JS LANDSCAPING
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  #55  
Old 06-08-2006, 11:18 PM
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Gatewayuser Gatewayuser is offline
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Location: Cincinnati, Ohio
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I went to the funeral today for the man and some of the homeowners there said they are going to get rid of their Z's.
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