<top posting only because the auto student is>
pkurtz,
You are taking my examples *way* to literally. The reason I put
"normal driving conditions" in quotes is because I know there is no
such thing. How about average driving conditions? You know, that
state it which the vehicle is most often driven, that work for you?
And when I referred to the three wheeler's, that was just another
example. So no, I wont be able to provide an identical car on the road
that you ask for. That was never my intention.
Your argument still falls flat (no pun intended) to me.
Harder tires (more inflation) equals better milage. Softer tires (less
inflation) equals worse milage. On average.
To take it to some extremes. If you are driving on ice, then an under
inflated tire may increase your milage, as it provides a bigger
footprint, thus more traction, and without traction, you'd be
slipping. Of course your milage would be way worse than normal, but
you might be able get somewhere.
On the other hand, if you are driving around in a place with little
precipitation, let alone the frozen kind, then a smaller footprint
would be good for your milage, and you *can* achieve this by
overinflating your tires.
Not saying you should, mind you, you do have to factor in the altered
wear. Higher risk of puncture, and most likely shortened life of the
tires. And of course, less foot print equals less effective braking.
I really just don't buy your argument that there would be significant
"slip". If your driving so fast that your vehicles tires are leaving
the road surface, then you aren't too worried about milage I'd guess
:) And even at moderate speeds, wouldn't inertia negate most of the
alleged "slip"?
You used the word "exponentially" twice. As that is a mathematical
term, and you are an auto student, I suppose you could produce the
study or research that provides those numbers. You probably have
easier access than I would, so I'd appreciate seeing them, or links
to them.
And if you're curious about the comment I put at the top of this post
in <>'s...
http://en.wikipedia.org/wiki/Top-posting
Don
On Tue, 17 Jan 2006 12:03:44 -0600, "pkurtz2" <pkurtz2@cox.net> wrote:
>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.
>
<snip>
