pkurtz2

Don,
I hear what you are saying, but lets look at a couple of other things. You
say "Under "normal driving conditions"?" and in return I say "What do you
consider normal driving conditions?" When you look at the fuel ratings on
car stickers, you get the milage that the car would get under "Normal
Conditions", but there is NO SUCH THING. If you look in the owners manual on
every car manufactured and read what normal driving conditions are, you will
find they dont exist. There is no place on earth that one can find "normal"
driving conditions. Now when you talk about the amount of slip on the tire
from an overpressurized tire then you have to take into account several
factors. Some of these would be speed, wind direction, wind speed, drag,
weight of the vehicle, etc, etc.... If you look at the electric cars that
race, the reason they only have 3 wheels is becuase they are extremely
light, and are balanced according to their design, this also helps cut down
on drag. If you can point out ONE electric (completely Electric) car on the
road today that is IDENTICAL to one of the cars that has raced in one of
those races then I will bow down, but I dont think you will. You will also
notice that those cars are designed to have no drag on them. Cars require a
certain amount of tire on the road to prevent slip, to the amount allowed by
the car designer because of the factors I have listed above, Especially when
it comes to trucks. The other thing you have to look at when it comes to
trucks, is that the drive wheels are on the rear of the vehicle, not the
front. This reduces the amount of down force on the drive tires, and
increases the amount of slip exponentially. So if you overinflate your
tires, especially on the rear of a truck, then you have increased the amount
of slip exponentially. The major problem with this is that roads are not
perfectly flat, thats why we have shock absorbers and moveable suspension,
and when you hit a bump, the rear of the vehicle comes down at a slower rate
than the front. This increases the amount of time that the front
(non-driven) wheels are on the ground, and the rear of the vehicle is in the
air.. Now if you reduce the amount of air in the rear tires, to specified
pressure, then the tires do part of the shock absorbers job, and thus the
rear tires stay in contact with the ground more, and have less slip.

I hope this answers any questions you have.

p.s. there is also slip created from the mechanical drag caused by the front
wheel bearings, brakes, 4X4(if applicable), the rear wheels have to push all
this, and overinflating them will also shorten tire life as well as reduce
gas milage.

"Donut" <Donut@donut.net> wrote in message
news:6m8ps1pbgsglplrhg4nr0looesj5n1oegj@4ax.com...
> On Mon, 16 Jan 2006 22:53:30 -0600, "pkurtz2" <pkurtz2@cox.net> wrote:
>
>>Mark,
>>Keep in mind that OVERINFLATION of your tires will actually HURT your gas
>>milage.
>
> That seems counterintuitive.
>
>>The reason for this is because it changes the "footprint" of the
>>tire on the road, or the amount of tire you have in contact with the road.
>
> I'm with you here. Less "footprint" equals less friction. Less
> friction equals better milage.
>
>>Overinflating tires lessens how much tire is on the road and contributes
>>to
>>slip. The more slip you have, the worse milage you will get.
>
> This is where you lose me. Yes, if you have a lot of "slip" your
> milage will suffer. But are you really saying that you *are* going to
> have a lot of slip with (slightly to moderately) overinflated tires?
> Under "normal driving conditions"?
>
> Every time I've looked at milage competitions or solar car
> competitions, invariably the winners had hard skinny tires, they
> aren't going for comfort here. And a lot of times, just three wheels,
> an easy way to get rid of 25% of the milage robbing friction in the
> design :) I would be interested if you can prove them wrong.
>
>>Go with what it says on the door sticker for your tire pressure.
>
> Hard to argue with that, but there are "tweaks" we can try :)
>
> Don
>
> <snip>