GardenBanter.co.uk - View Single Post - Garden/Lawn tractors grip, tire pressure and alignment

Dave · 28-09-2007, 05:31 AM posted to alt.home.lawn.garden

"Clark" wrote in message
...
wrote:
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.

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...

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