As pointed out by rigid in a response to my first article, vehicles rarely if ever evenly distribute their weight among their four wheels. Even sitting still it will have its weight distributed a bit to the front or rear, to one side or the other, and will even have something known as cross weighting upsetting the balance.
A perfect car would have each wheel with exactly the same weight on it at all times, unfortunately this is impossible, but every attempt to get closer to it usually results in a better handling vehicle.
I say usually, because sometimes weight transfer is good, i.e. when you accelerate in a rwd car, shifting weight to the back aids in traction to the driven wheels.
As a car sits still, there are a few factors that could and do effect its weight distribution. The first of which is COG (center of gravity) location. A vehicles COG is the point of the vehicle where if you lifted it, it would balance. This is the perfect balance point where if you slowly started turning the car, it would still be perfectly balanced.
A vehicles COG is a VERY important concept. By using it, you can determine a vehicles weight distribution, roll forces, pitch forces, yaw forces... etc etc.
But how do we find out where a vehicles COG is? The easiest method is by using weight scales (that are strong enough for your car) and a digital angle finder, if you have access to a tilt table you are in luck! Otherwise any flat sloped surface will work.
The first measurements you should take are the weights of all four wheels. Summing the two front weights and dividing by the total weight will give you the front weight distribution in a fractional form. To know exactly where it exists simply take the distance between your front and rear tires and multiply it by that number. The number you get is the distance from the rear wheels to the plane the COG exists in.
i.e.
((FL+FR)/Total Weight)x(Front to Rear Wheel Distance)=Distance from rear tires to COG
likewise
((FL+RL)/Total Weight)x(Left to Right Wheel Distance)=Distance from right tires to COG
Next, line up the vehicle either vertically or horizontally to the given slope. You only need one of these directions to calculate how high the vehicles COG is. Record the weights and measure the angle the car is at.
For calculations, repeat the previous calculation but with the new weights, this will give you the inclined distance.
Now for the magic.
(Flat Distance-Inclined Distance)/tan(angle of incline)=COG height!
If you end up with a negative COG it just means that the car was facing downhill or the left side of the car was downhill ;) just ignore the negative sign haha.
There are two more things that I know of that can possibly effect static weight distribution.
The first is cross weights, and the second is if your vehicle has a preloaded sway bar... which should only apply to oval track cars...
To understand cross weights the easiest, picture a table. If you lift the table by one of the legs, which leg will generally take up more weight? Chances are it is the one on the opposite corner ;) Cars are much like tables, being that they have four contact patches and if you lift one up the opposite corner will get loaded more.
This is all fine and dandy, but doesn't explain why your car has a cross weight (it could be either big or minuscule)! The thing you probably haven't thought about yet is what would happen if the car wasn't perfect? What if when it was built the springs were slightly different, if the chassis warped the tiniest bit from welding, or any of the other thousands of tolerances were a tad bit off, yet still within an acceptable range for manufacture. Truth is, all cars are like this. Yes even Porsche's hahaha.
It's like saying you can't cut a string ten centimeters long, you can get close, very close depending on the amount of time and effort you put into the cut, but you will never ever make the string exactly 10cm long. This applies to cars, every car will have some cross weighting due to construction, but generally the amount is negligible. If you have ever touched the car's suspension however and don't know about cross weights, chances are you disrupted its balance, and probably need to take a look at it.
So what do you do if you realize that the front left and rear right corners are taking more or less weight overall then the other two?? Well the easiest way is to adjust the preload in any of the springs, but the best way would be to adjust the suspension geometry. For example, the formula car in the picture below has adjustable push and pull rods which raise and lower the suspension at each corner.
Now as to preloaded sway bars, in stock cars they force the outside front right tire down, this puts additional weight on the rear left tire. In stock cars this is a good thing, it evens out the weight distribution in the back a bit and gives more grip to the rear wheels.
And there you have it, Static Weight Distribution!
Next Discussion will be on Dynamic Weight Distribution :)