beanbag

Recently I've run across a couple of posts where some people make corner balancing the car out to some big complicated mess, where you have to adjust something a tiny bit, put it back on the scales to check, check the heights, re-adjust again, etc. That sounds like a big PITA to me. I called some shop to ask how much it costs, and the guy was like "$175 and 2 hrs". WTFLOLBBQ. This is supposed to be science and not art, and you should be able to get it right in one shot, and maybe a second shot for some final tweaks. Anyway, the procedure is pretty simple if you approach it from the right mindset. Here goes...

The main paradigm to get is the concept of "eigen" operations, which means that there are certain sets of adjustments that you can make that will only affect one aspect of the car, but will leave all others alone. When you figure these out, you can combine all of them in one fell swoop, and their effects add as you would expect. You have 4 height adjusters, and thus 4 sets of eigen operations. They are:

E1: raise the entire car evenly 1" all around
E2: raise the front 1" and lower the rear 1"
E3: raise the right side and lower the left side
E4: shift diagonal weight without changing any of the heights

These operations are completely independent of each other. For example, E1,E2,E3 don't change any of the corner weights. It's easy enough to figure these out, and thus you can easily level the car without changing any of the corner weights.

First off, you may as well measure the car, and measure the corner weights w1-w4, the corner heights c1-c4, and the spring perch adjuster positions h1-h4, all relative to some point (it doesn't matter which).
For now, I have the car labeled as such

front

1 2


3 4
rear


For each corner of the car, the corner height c is the sum of (the spring length s and the adjuster height h) divided by motion ratio mr (where motion ratio is values less than 1). However, the absolute value doesn't matter, and only changes in the quantities matter, which I will denote with a d in front (means delta). Thus:

dc=(ds+dh)/mr.

The operators E1-E3 don't change any of the corner weights, so the spring lengths don't change.

Under these conditions, dc=dh/mr

Hold on, this doesn't mean that you can just raise a corner 1" by raising that adjuster 1"*mr. The above equality only applies if you use the E1-E3 operators. To figure out the effects of these operations, we need to find out the effect each one has on the corner heights, and then reverse calculate the system of equations to figure out how much of each operation we need to apply to get the corner heights we want.

The coefficients of the operators are A (for E1), B (E2), and C (E3), where the value means "how much of the operation we apply".
For example, look at corner 1. The equation is:

c1+A+B-C=c1+dc1

In words, this means that the final height c1+dc1 is equal to the initial height c1 + A (raising the overall height raises this corner) + B (raising the front raises this corner) - C (this corner is tilted downwards). Cancel out c1, since only the height change matters. For the other three corners:

A+B+C=dc2
A-B-C=dc3
A-B+C=dc4

Right now, there are 4 equations and 7 variables. However, you get to pick three of them, that is, three of the corner heights when leveling the car. The 4th corner you can't independently choose because you assume the chassis is stiff and you can't bend it (more on this later). So now there are only 4 unknowns. This set of equations is not very hard to solve, and eventually leads to:

A=(dc2+dc3)/2
B=(dc1-dc3)/2
C=(dc2-dc1)/2
dc4=dc2+dc3-dc1

multiply all the c's by their respective mr to get h's

As an example, pretend that you want the raise corner #1 by 1", #2 by 1/2" & keep #3 the same, and 4 will turn out to be whatever. I'll save you the trouble and point out that yes, you really do raise the corner #1 adjuster by 1"*mr, corner #2 by 1/2"*mr, and leave #3 alone. However, YOU MUST ALSO FOLLOW THE 4TH EQUATION, which means you HAVE to drop corner #4 by 1/2"*mr in order to keep the corner weights (also avoids flexing the chassis).

--------------------------------------------------------

OK, now you are done with operations E1-E3, and have levelled the car. (Obviously, this is all still on paper.) Now to go on to E4 and shift the diagonal weights. It seems kind of complicated to figure to how to do this operation, but it's really not. First, you have the equation that says that the corner heights stay the same, but the adjuster position and weights (therefore spring length) can change:

(dh + ds) / mr = dc = 0

Another equation says that the change in corner weights is related to the change in spring lengths (since that's what holds up the weight)

dw = -ds * sr (spring rate) * mr (no ^2 on the mr, I think)

Combining the two gives:

dw = dh * sr * mr (for each corner)

Finally, the only equations you need to know are mass conservations:

dw1 + dw2 + dw3 + dw4 =0 (total mass conserved)
dw1 = -dw2 (front end mass conservation)
dw1 = -dw3 (side mass conservation)

3 equations and 4 variables makes sense because when shifting corner weight given these other constraints, you only have one degree of freedom, i.e. the diagonal weight transfer. So just pick one corner to add or remove weight from, and let the equations do the rest. For example, choose dw1. Then dw2, dw3, and dw4 immediately pop out. Note that if dw1 is positive, so is dw4, while dw2,3 are negative. Go up to the previous equation, and all the adjuster heights come out. Add these values to the ones you came up with in the previous section.

Done

Or, if not done, at least it should be pretty close. One possible source of error is when you lift the car and the springs unsettle, they might resettle in a different location. Oh well.

Disclaimer:
0) I might have made minor or major mistakes along the way. The general principle is still correct, though.
1) I made a few assumptions along the way. If you can pick them out, you are certainly capable of correcting for them.
2) I have never corner balanced a car in my life, nor watched anybody do it. You are free to decide for yourself if you believe what I wrote above.
3) Maybe this info shows up in some race car engineering book somewhere... I dunno since I don't read them.

Some other issues:
A) What about the forces that work to bend or twist the chassis?
-short answer: The chassis seems to be pretty stiff. It feels like at least 2000 lbs/in or more to bend out a corner on an Integra frame. With some more math, you can add it's effects to the E4 operator.

B) So should I disconnect the swaybar while doing this?
-short answer: it depends

C) What about adding ballast?
-whatever

Egezzy

iTrader: (2)

damn this was the first thing i did today. read this as soon as i woke up. but anywho. i like how you stated to adjust 3 sides and let one stay static(obviously you would have to have it at a height you like first). i know many people who adjust and adjust by running around all four corners(this is for normal alignment stuff not corner balancing) and one small adjustment f.s their previous adjustment. i liked the whole writeup. the only thing i am confused on is how you stated that once you had the heights figured out that you could adjust the springs at that point without affecting ride height. am i still asleep or did i read it wrong?? lol.

beanbag

If you assume that the chassis is very rigid, then yes, you can adjust the springs to transfer diagonal weight without changing the chassis height at any corner. For example, if you want to add weight to the 1-4 diagonal, you raise the adjusters at 1 and 4, and lower 2 and 3. When you go back to corner 1, the chassis will be back at the same height.

Things are only slightly more complicated if you assume the chassis is floppy. You will "taco" the chassis by bending corners 1 4 upwards, and 2 3 downwards. The amount of bending is D, a.k.a. the "chassis taco factor", where

D = dw1 / k (k=chassis taco stiffness, maybe 2000 lbs/in or higher?)

Go back to the equations with A B C, and now add in D, for example

A+B+C-D=dc2 (this corner is bent downwards)

p.s. Apparently, this is for the American style of taco's, which are curved. All the Mexican ones I have seen are flat.

slammed_93_hatch

Have you ever actually corner balanced a car?

Like had a car with a scale pad leveled out, and actually corner balanced it?

solo-x

Nope. He actually admitted that in the disclaimer. It was the only part of the post I read when I realized how much he had written. Everything is SO much easier in theory!

beanbag

slammed_93_hatch

I didn't really even read it.


Just saw tons of equations, and things that i know are wrong and stopped reading.

Johnny Mac

The simple theory behind corner balancing is that to find four vertical wheel loads, you have to use three equations of equilibrium, which states that the sum of the vertical loads equals the weight of the vehicle. In addition, two equations are required that sum the moments (which also equal zero): one lateral and one longitudinal). Now, since you have three equations and four unknowns, you must use a deformation analysis to determine the last equation. In engineering, the car's suspension is an indeterminant system or a redundant system of order one. The deformation analysis is done on the each of the suspension springs if we assume that the chassis is rigid.

This is why a trike or three wheel vehicle is statically stable and is determinant (i.e. no deformation analysis required) if the the center of mass lies within the triangle defined by lines connecting the three wheel contact patchs.

slammed_93_hatch

Interesting,

I am much more of a "do it" type of person.

Stinkycheezmonky

I always thought the "difficult" part of corner balancing was finding scales to use...?

california dude

WOW




b.

beanbag

Ohhh, the irony. It burnsssss.

essex

I agree

slammed_93_hatch

I went back and read yours too and that is what i was interesting too. The whole "idea" and "theory" is interesting.

Still doesn't mean that knowing any of this information is needed to know in order to corner balance a car.

Johnny Mac

Well as I think you know Jimmy, I also corner balance my own cars and align them with strings as well. It's just nice to know there is a theory behind the whys and whatfors of some of the things we do to our cars to make them perform as close to optimum as we can. And you really are correct in that you don't need to know the theory of corner balancing to do a great job of setting up a car.

EdoMoto

I was given this little Excel program that takes out the whole guesswork out of corner balancing a car.


Edo

NTCustoms

edo, if you could host it somewhere, that'd be great!

essex

http://www.google.com/search?hl=en&q...meta=&aq=f&oq=

NTCustoms

cool!

solo-x

Now, for the real questions.

1. Is there any point to corner balancing your car if you use floppy OEM control arms, rubber bushings that bind and have a spring rate of there own, and a host of other suspension compromises.

2. In a car that is inherently left biased and front biased AND front wheel drive, is a 50% cross really ideal? What if you're forced to use an open diff, does that change anything?

slammed_93_hatch

I agree

Andrie Hartanto

Is this what it takes to make you come out and post? Only 3 words to boot!

Johnny Mac

He's the short answer man. The question really is, what comment garnered the WOW factor? What it the OP's opening statements? Or something Jimmy had to say? I'm sure it wasn't me since he's been around me long enough to ignore most of what I say anyway.

Stinkycheezmonky

Only thing to add, and just a point of information: On a K20-powered Integra we set up recently (essentially an H1 car), we got 50/50 Left/Right weights with driver in the car without moving anything around as ballast. Kind of interesting, and not what we expected. Regardless, I'm interested in the actual answer to your question.

beanbag

Given the mis-match between theory and practice, the correct thing to do is work with what you got and not throw up your hands and just give up coz it's too hard. ("Giving up" refers to the trial-and-error adjust-one-corner-at-a-time method of corner balancing.) If one is willing to expend some token mental effort, then the easiest solution is the one that converges to the final configuration the fastest, even in the presence of unknowns like bushing flex and floppy control arms.

If you know of some other method or technique that can achieve the correct corner weights and heights quickly and with minimal labor, then I'd like to hear about it.