On Thu, 25 May 2000, Randy Chase wrote:
> *warning....possible detailed techno-geek stuff follows*
>
> Iain Mannix wrote:
>
> > Raising/lowering/front/rear.
> >
> > Byron Short once used a big hammer to convince me that raising one end
> > of a car would make that end heavier. It is true.
>
> In what way did his hammer convince you? 8-)
He would'nt shut up until I agreed;).
>
>
> You can do it with
> > two bathroom scales and a sawhorse(or anything that is relatively
> > heavy that will not allow the mass to shift). Put two legs of the
> > sawhorse on one scale, call it the front. Put two legs of the
> > sawhorse on the other scale, call it the rear. Sit two
> > bricks/dictionarys/heavy things on the sawhorses over the legs.
> > Observe "front and rear" weight.
> >
> > Take the brick off the top of the sawhorse on the "front" scale, put
> > the brick *under* the legs of the sawhorse, raising the "front" three
> > inches(or however tall the brick is).
> >
> > There are still the same things on the scales - one sawhorse, two
> > bricks - but the weight will change; not total weight, but
> > distribution. It really works.
>
> Ian, I respectfully suggest that this is an incorrect method of
> demonstration. In one case, the scale is measuring roughly have the
> weight of the sawhorse, and part of the weight of the bricks, because
> the bricks load is shared by the sawhorse, and therefor distributed to
> both scales. When you put the bricks under the sawhorse, the main change
> comes from the one scale weighing 100% of the bricks, instead of have
> the load shared.
>
OK. That's fine. Short answer: put your car on scales and manipulate
the ride height:).
Longer answer(and less problematic for you Stock types without "m030"
in your .sig file;); rig up some sort of device which is telescoping &
try the same experiment, or cut the legs of a swawhorse(a real one,
not some fancy black & decker thing), drill a bunch of holes, make
a Street Prepared sawhorse - use some sort of bolt or something to
be able to change the height of one end relative to the other(maybe
use bricks or heavy immobile weights to get bigger readings - bigger
is better, right?).
> I also disagree with the basic point, but I am willing to be shown in
> what way I am wrong. It has always been my grasp, that in order to do
> less work while appearing you are carrying the same load (hehe) when
> carrying sofas or other heavy furniture, you should raise your end. The
> higher end weighs less.
>
I always grapple with that one, too, as it is easy to visualize, but
it does not really work "correctly." It probably has a good bit to
do with the fact that the couch moves as the person on the stairs
goes up.
> This seems simple when viewed simply. If one takes a long heavy object
> and tilts it, eventually the higher end has almost no weight, and all
> the wieght is on the lower end. Now a car is a little more different, in
> that you didn't raise the entire car, you just changed it's location of
> mass and center of gravity. The tires still rest on the ground. There is
> also further complication because the higher end, though exhibiting
> slightly less force downward, will be affecting by suspension changes
> and the higher center of gravity.
>
I'm not a physicist by any stretch. I can't currently think of a better
way to describe it; the orignial means I used(cable in particular) are not
100% accurate/correct(I think I put some sort of disclaimer there), but
they're the best I can come up with right now.
Yeah, sorry, maybe tomorrow I'll be better able to put it into words.
Someone here might be able to put it into words.
I do know that when I raise the rear of my Rabbit, the back wheels
get heavier(I raise it through coilovers, not heavier springs). It
really does work; sorta like cornerweighting, when you raise the RF ride
height, the LR gets heavier, and the opposite corners get lighter - that
one is far easier to visualize, but it is really no different - as
you raise one end, it gets heavier. Think of the springs pushing down
harder on the ground? Not really what is happening, but it might
help; as the ride height at the rear goes up, those two springs have
to lift more than the front, as the car cannot slide down; the mass
cannot move down to the front wheels.
Dammit, I used to be able to explain this easily.
Shrug, dunno. I'll leave it to the masses to explain; either I'm
right or my Rabbit defies the laws of physics(or all the scales
my car has ever been on work backwards, showing a bigger number when
weight is reduced;).
> If I am missing something, please let me know what it is. I am not
> trying to debate the point, just understand why something I have thought
> for many years may be incorrect.
It took me a while to really understand it. I wish I could explain
better.
Iain
>
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