Joe Weinstein

Hmmm. I think I have it, and I think the cross-weights can be equal,
no matter where the GC is. Here are the four equations and four
unknowns:

for my 35/65 f/r 60/40 l/r 3000lb car, we know that

1 - front: LF + RF = .35 * 3000 = 1050
2 - rear: LR + RR = .65 * 3000 = 1950
3 - left: LF + LR = .6 * 3000 = 1800
4 - right: RF + RR = .4 * 3000 = 1200
5 - whole: LF+RF+LR+RR=3000

Now if we posit:

6 - LF+RR = RF+LR

that means that each side of this is 1500.

7 - LF+RR = 1500
8 - RF+LR = 1500

So substituting in, we solve for the four
values and get:

LF = 675, RF = 375
LR = 1125, RR = 825

Everything is satisfied, and the cross-weights *equal*.
So it looks like that anyone doing a corner-weight
job had better have a specific track-based reason
why they are are not getting the cross-weights equal,
because they are in effect biasing the cornering capability
of the car to one side or other like NASCAR.
Joe

Matt Romanowski

Joe - Use a set of scales with an electronic read out. Select a diagonal. Look at the weight percentage. Change until it's 50%. Done.

Joe Weinstein

Yep, so it seems. It's good to know what each corner *should* read
so you know which wheel of a given diagonal is most out of whack.
Joe

Nordschleife

Sorry about that - i was grabbing figures at random as the files on this with actual data were deliberately kept closed.

But the principal applies, minimising the difference between the two diagonal weights is the way forward.

Points to consider include:

What is the weight difference between different drivers if enduro racing - when running multicar teams we try and match drivers for size and weigth as well as a mix of young eyes and old eyes.
Where in the race/stint do you want the best balance - start, mid race or finish (on worn tyres)

So you weight your car to suit what you desire - the right ballast for the driver, the right amount of fuel in the tank when you corner balance the car. If you have tall and short drivers and move the seat for them, take account od this. I believe this is particularly important in North America where there are a number of teams with large tall patrons and small compact rock star drivers.

R+C

Joe Weinstein

Thanks again Nordschleife.

I have a new option I'd like your opinion on. As I understand it,
as long as the car's spring rates are matched side-to-side, it
seems to be that the geometric, natural balance of LF+RR=RF+LR
once dialed in, should stay the same even if you add or change
weight because any added weight will just be applied to each
corner according to their natural proportions. The only thing
that a different driver weight might change is the anti-sway bar
attachments, so the bars aren't transferring any torque at rest
with the changed load.
The new idea I would like you to consider, is to *not* go for
a LF+RR=RF+LR, but instead try to get the ratio of LF/LR to equal
the RF/RR ratio. This would make the basic front-rear weight rel-
ationship the same on either side of the car. This (I think) has a
major benefit because most of the other things we do to make a
car neutral, we do as if it will affect both sides equally, like spring
rates, shocks, bars, alignment etc. If the front/rear weight relation-
ship is different on the left than on the right we may have a car
that is neutral turning one way and not the other. I do understand
that if we try this 'unnatural' balance, that then we must do this
with the car weighted as it will be run because changing GC location
will alter any such 'engineered' balance. I also understand that this
may have a negative effect on max braking or acceleration because
it may make the LF/RF and/or LR/RR ratios get farther away from
1.0, but this *may* be worth it. For example, with my 35/65 front/rear,
60/40 left/right 3000lb car, the 'natural' balance is:

LF=675, RF=375
LR=1125, RR=825

(LF+RR=RF+LR)

Note that the LF/LR ratio is 0.6, and the RF/RR ratio is 0.45!
That sounds like a car that would act differently in left turns
than right ones.

How about tweaking the preloads till we get:

LF=630, RF=420
LR=1170, RR=780

Here the cross weights do not match. The are off by 180lbs.

However, LF/LR = 0.54 and RF/RR = 0.54! That looks like a car
that will behave the same in left and right turns. In addition,
in this case it looks like the max braking will even be better
because the two fronts are closer. Max acceleration will be
hurt because the rear difference has gotten wider. Maybe
this is a good tradeoff? I am going to try this with my car.

Joe Weinstein

Adam@Autometrics

Looks pretty similar to your last example...
The fact is, there is no one way to corner balance. No matter how you break it down, you have 4 variables with only 3 independant equations. Any way you do it will have compromises. Like all racing, the fastest cars are the ones who made the best compromises.

Nordschleife

if I understand you, I would say that if you add weight at the car's balance point, the corner weighting will remain in the proportions that you set it in. However, if you were to add weight anywhere else, it would alter the proportions you set the car up with.

Well, try and set the car up this way, and see what happens........

Cars are not built symmetrically, neither left right nor front rear.


R+C

PS move as much weight as possible in towards the centre of the car and as low as possible, get your car several hundred pounds underweight and ballast up to allowed minimum weight. Don't let fat bastard drive the car.

Joe Weinstein

Hi, no, I'm predicting that:

For a car on the scales with it's anti-roll bars still detached,
if it has been corner-balanced to the natural balance (LF+RR=RF+LR),
then if you put some more weight in the car, or take some off, *anywhere*,
the LF+RR=RF+LR will still be substantially true. This is because the
balance reflects the geometry of the car so new weight will be distributed
according to the geometrics of where it is from each corner. I hope the
next time someone has a car on the scales, they can verify this. Add
200 bs somewhere odd like the trunk, and see if the corner-balance
really changes much.
You are right that we are dealing with the asymmetry of the car,
and that won't change except if we can actually alter the load with
ballast etc. And unfortunately *I'm* the fat bastard that it has to
work with... The LF/LR=RF/RR idea is not natural, so it will alter
with load. New load will be distributed geometrically, not according
to the LF/LR proportion...
Joe