Garden/Lawn tractors grip, tire pressure and alignment

After reading many posts complaining about front tires skidding rather than turning, I found I should throw in my 2 cents.
When I rode my Sears garden tractor (those have lower-profile tires) for the first time, it felt like go-karting on an abandoned log road. It turns out that there was 17psi in all 4 tires, while the markings specified 10 and 12 psi. The tires were sitting on the pavement perfectly round, and the contact patch must have been about 3" by 3".
On relatively hard surfaces like mature lawn, the grip is directly related to the contact patch. After I dropped the pressure to 8 psi (I like a comfy ride but not a flat beer) the contact patch looked like it more than doubled. Although I did not have grip problems, that would certainly have helped.
In another post I described the excessive toe-in my front wheels showed when I got the tractor. We're talking 3.2 degrees. You need to hit an SUV with your car to get that kind of toe-in on it. Although there are opinions that toe-in helps steering response in turns, I doubt it is intentional because of the cost in straight line stability. If toe-in really helped, the technique would be used in car racing (although they do use skewed camber and caster adjustments).
The wheel spindles geometry already takes care of turning the inside wheel by a greater angle than the outside wheel, so each gets its own turning radius for maximum grip. These angles are carefully calculated based on parallel position at 0 degrees and are a function of the track and wheelbase. Any toe-in or out throws off the two turning circles for less optimal grip.
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On 9/27/2007 9:38 AM, snipped-for-privacy@hawk.igs.net wrote:

<snip>
Toe in will tend to keep a vehicle going in a straight line, helping high speed stability. Excessive toe in will make a vehicle (lawn tractor in this case) hard to turn, with the front wheels trying their best to stay centered with respect to the rear. I imagine that 0 degree toe in would help turning at the expense of a sight tendency to wander whilst going straight.
--
Ted
I wasn't born in Texas but
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wrote:

If it was critical on a lawn tractor they would have retained an adjustment feature.
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They did, but it's on the other tractor, the one you would have paid two or three times the price.
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$4,000 - $6,000 ? Are you talking Kubota compact ?
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snipped-for-privacy@hawk.igs.net wrote:

and I thought I was anal retentive about my lawn care machines. Damn it, now I have to go out to the barn and check the toe on the Craftsman and the Toro.
Clark...
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wrote:

Before he passed away, my uncle owned an automotive garage. My dad and my uncle had a conversation about front end alignment. Evidently, whether the driver is in the car can play into that. How much is this reflects on a riding mower's toe-in, I'm guessing much more. So, put a few of bags of sand on the driver's seat before checking toe. Put that in your pipe and smoke it. Rest of the clowns too. Dave
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You're absolutely right Dave! On a vehicle with independent suspension like most cars and trucks, the toe is affected by the vertical position of the wheel by virtue of the geometry of the suspension. I've always been sceptic about the method of aligning an empty car. When the heck is a car empty while it moves??? I'm having no more of that. My crown vic had its first alignment at 70k and showed a slight more wear toward the inside. After the "aligner" told me he did not need to touch my toe, I told him to please pardon me for asking him for removing 0.1 deg to the toe. He asked why, then told him that you can't tell people to get their car aligned so their tires last longer, and at the same time completely ignore wear on the tires when the car is aligned "right"! He reluctantly removed the .1 deg, and now my tires wear evenly. Your Uncle knew that.
A garden tractor is has no suspension Dave, hence toe is unaffected by load. This clown rests its case.
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