* CORNER balanced - numbers from this...and the weight

[Zeke]

Originally posted by Randy Blaylock


By the way, there is some good racing on Speed right now.

In fraternity....

[Randy Blaylock]

I'm in total agreement with your two stated facts. Weight jacking doesn't change the fundamental weight distribution front to rear, or side to side.

I'm not sure what the derivation of apportioned weight is though. How do you know what it's supposed to be? Do you attach solid links in place of the shocks and struts that are exactly the same length, and then measure the corner weights on a perfectly level surface?

If you mean that you measure the total left side weight, and total front weight, for instance, and then use a mathematical formula to determine what the left front corner should be proportional to these percentages, then I have to respectfully disagree with that strategy.

Weight transfer will only accentuate these biases, making the inequities larger, which will promote uneven total grip potential in each corner of the chassis.

Using the method of big numbers to illustrate a point, and the apportioned weight model, let's say we have a 1000 lb chassis w/driver, and the driver and engine are mounted on the LR corner so that the left side weight total is 95% and the rear total is also 95%. Using the apportioned weight model, the LR would weigh 902.5 lbs, the LF is 47. lbs, the RR is 47.5 lbs, and the RF is 2.5 lbs. it's obvious on the face of it that this is not a well handling machine. Put the brakes on and the RF will lock up all day long.

Just something to think about.

[Wil Ferch]

Randy:

I followed you totally until you gave your last example...

Big numbers or not ...your example cannot co-exist in real life.

A car can't have BOTH 95% of it's TOTAL weight on the left side..and ALSO 95% of its TOTAL weight on the rear.

How do I go about "Apportioning" weight? If your remember as far back ( ! ) as one of my first postings on this thread....I said I worked up a long math means of calculating this...and Chuck Mooreland's method was a "short form" that ended up the same way.

Since you'd like to see a "derivation" of how this came about...let's start with the two facts that you say we're in agreement with:
1.) Total front ( or left side..or right side..or total rear) weight stays the same regardless of the corner balance achieved. Doesn't change for any TWO ADJACENT wheels.
2.) a heavy LF will result in an equally heavy RR (etc)

So....For a 1000 lb car with a 40/60 front/rear weight distribution.....and a 51% left/49% right weight distribution....the "ideal" weights would then be this:

LF = 0.4 x 0.51 x 1000 = 204 lbs
RF = 0.4 x 0.49 x 1000 = 196 lbs
LR = 0.6 x 0.51 x 1000 = 306 lbs
RR = 0.6 x 0.49 x 1000 = 294 lbs
_________
Total weight = 1000 lbs

This should be ( IMHO)..the "target" weights for a properly corner-weighted car.

If, for example....you put individual scales under each wheel and find a different number.....you may find ( for instance) that the LF is 25 lbs "heavy". If so....the diagonal opposite LF will also be 25 lbs heavy...the RR will be heavy. Because any two adjacent wheels stay the same..the other diagonal will be 25 lbs "light" ( from ideal) at each corner. Let's see if this is true:

Lets say Actual LF is 25 lbs "heavy" vs ideal, or = 204+25= 229
Since "total" front weight remains at 400 lbs...the RF has to be 400-229= 171

Since Total left side is .51 x 1000 = 510...then LR has to be 510-229=281

Since total right side stays the same at 0.49 x1000= 490...then RR is 490-171 = 319

So our "actual" numbers might be these:
LF= 229
RF= 171
LR= 281
RR= 319
__________
Total = 1000 lbs - checks
Total left weight is 229+ 281 = 510 lbs = 51% - checks
Total front weight is 229+171= 400 lbs = 40% -checks
Total rear weight is 281 +319= 600 lbs = 60%-checks
Total right wieght is 171 +319 = 490 lbs= 49%- checks

So...we can see that the "Actual" weights still show a 40/60 front /rear balance..and a 51/49 left-to-right balance, just as the first case....but the LF and RR are each 25 lbs heavy...and the RF and LR are each 25 lbs light.

The first set of numbers are the "target"..and the second set of numbers are what you might find going "in" for a corner balance...

ALL THIS ..... is identical to Chuck Mooreland's elegantly simple use of the short form... ( LF/LR should= RF/RR )

The question remains....doing this will likely set the two front wheels "not equal". I'm still undecided if this helps or hurts threshold braking, for the two opposite reasons given before.

- - Wil

[patkeefe]

I'm a bit puzzled by the assumption that any two adjacent wheels carry the same total. In reviewing real numbers on corner balances described in these posts, it is not apparent to me that this is the case. Perhaps I have misunderstood the meaning of the "any two adjacent wheels".

Also, if two wheels on the same axle are unequally loaded, how could they possibly dissipate the same amount of energy during braking?

Thanks!
Pat

[Randy Blaylock]

My example should have included the word bias with the 95%. In this case the example works. It illustrates the shortcomings of a proportional model relative to the objective of having a truly balanced chassis. Of course no one would ever design something so silly, and your numbers are close enough in real world examples that the distinctions are really quite small, and possibly not relevant.

I'll stand by my practical methods as they have been supported by measurable results and substantiated by data collection.

[Wil Ferch]

The real question, however, Randy....is even though your personal experience using these practical methods have worked for you in the past......is there still a better way that might work even better for you?

I guess one wouldn't know unless you have practical experience with these altered methods.

And to Pat Keefe...the idea that any two adjacant wheels never change their TOTAL weight is ( for clarity).....NOT an assumption. It is fact based on the car's inherent make up...where the large masses are located. As said....a 911 has a typical 40/60 front rear bias...and no amount of corner balancing will alter that. The only thing that would alter that is moving actual weight around...like relocating a battery or where the engine sits. I agree...it's hard to understand, but as you noodle the numbers you'll find that it is true...especially if you factor in the effects on the diagonals that I mention. Quite the contrary (to your point that you don't see this to be true via example)...if you look at my last post example...it absolutely shows that in both the "before" and "after" cases.....the front ( total), an side( total) bias remained unchanged.

Wil

[Wil Ferch]

I guess we can summarize this by saying....

Craig did not get a "corner balance" job....by pure and classical definition..his car is not corner balanced....

However, he got a purposeful and thoughtful ( meaning...not by accident or misunderstanding) "weight jacking" from an experienced pro...to get certain characteristics ( good threshold braking performance)...at the possible expense of equal L-R turning characteristics.

Randy makes a good argument that his purposeful "weight jacking" compromises the RR loading ( ending up light)....but that there is so much static weight there already that the RR won't lock up in any practical braking test. Yet the result of having both front wheels loaded equally when braking is a definite plus. Good call, Randy...and I'm seeing better what you did.

EDIT: In addition, getting the front weights equal for good braking doesn't ( in Randy's view) unduly compromise the handling since the sum's-of-diagonals are within 100 lbs of each other. Meaning?...although achieving equal front loading compromises "true corner balance", the amount of the compromise isn't bad..especially when you gain such braking goodness that you will *always* notice.

So....I'll give this a rest and maybe became a bit smarter as a result. Craig...maybe the title of the post threw me off at first and got me on the wrong track when you titled this "Corner balanced...etc". I started to challenge that this wasn't a proper "corner balance". Still true...but the trade-off you've achieved should serve you well...overall.

Craig...what you really got was a purposeful weight jacking to achieve certain vehicle dynamic benefits biased toward exceptional braking capability....so on this I stand corrected.

- Wil

[Craig 930 RS]

"Randy makes a good argument that his purposeful "weight jacking" compromises the RR loading ( ending up light)....but that there is so much static weight there already that the RR won't lock up in any practical braking test. Yet the result of having both front wheels loaded equally when braking is a definite plus. Good call, Randy...and I'm seeing better what you did."
[COLOR=darkblue]

The primary track I run at is extremely bumpy and in terrible shape; braking on an eneven surface was........terrifying.
I think the new found suspension suppleness and this front weight eveness will improve the situation -

[Wil Ferch]

Craig:

By all means..... report back any findings...good and bad....

- Wil

BTW---what *were* your corner weights before you changed to these numbers? Apples-to-apples....with you in the car.

[Craig 930 RS]

Not a clue - the car was set up so it looked and felt like a motorboat - high in front, low in back. I was pretty disappointed -

[Wil Ferch]

Craig:

I'm surprised....a lot of time and effort and $ on this work.....

...and you *don't have a baseline of where you started from?....

Do you think Randy or his crew ( ?) captured the first numbers on the scales ??...

- Wil

[larry47us]

OK, this is a subject that I know nothing about, but this past weekend, I loaded my car up on Souk's new bathroom scales to see what Kermit's balance looked like. Now, mind you, this is untouched from when I got it back from the restoration.

But, I was goofy enough to take some pix of it. Here's Kermit after we drove him up on the bathroom scales.



Here's the front of the setup.



And here's a shot of the display with the critical numbers.



Now I don't pretend to be an expert, but a stock 73 E with sport seats, heavy as they are, weighing in at 2437, with a nearly full tank isn't too bad!! Side to side balance at 49.6%/50.4% sounds to me to be pretty good. Front to back weight distribution at 39.4%/60.6%. That's before any work being done to corner balance.

I guess that I should smile now??

larry

[Craig 930 RS]

Wil......I could tell you stories of previous 'work' done on my car.....
But it'd just p-me off all over again

The old saying:
"If you want it done right do it yourself"?

Correct.

[Wil Ferch]

Larry:
Look at my my recent post where I give an illustration of two cases... before and after "corner balancing" a fictional 1000 lb car..

Did you notice something?

Like.....in ALL cases you can't alter the basic weight distribution? Either front/rear....or side/side?

What I'm getting at is that for the "properly" corner weighted car...( assuming apportioned weight is "proper")...and an "improperly" corner weighted car.....BOTH will show the same front/rear and side/side TOTALS.

Therefore...I don't know what you have as far as your read-outs are concerned...because I can't make out individual corner weights....just "one end" totals...which tell us nothing ! You might be good....you might be bad....dunno.

Can't make out "which" cross-weight you have either.

If ya got individual corner weights that you can show...let's see 'em and we can analyze....

- Wil

[larry47us]

Will:

I understand what you mean. Doesn't the "CROSS" percentage provide some of that? I will have to call and see if Souk wrote down those individual numbers. I think that he did, I just didn't copy them down. I'll update you.

larry

[Wil Ferch]

Okey dokey then...standing by...

BTW...Craig....wasn't bustin' on ya...just surprised, that's all. But I can *see* how you can end up that way...

- Wil

[Randy Blaylock]

Wil, there is no crew, it's just me.

There was no productive reason to record the original corner values because everything on the car has been changed, the spring plate and control arm bushings, the banana arm monoballs, the ride height and rake, the and the alignment settings. It would not be an apples to apples comparison.

I'd be willing to bet Larry's corner values will come in somewhere around;

LF = 503
RF = 456
RR = 776
LR = 702

FWIW, the individual corner values will be meaningless anyway unless that concrete garage floor is dead level.

[Wil Ferch]

Randy:
Thanks....I didn't know how to read "cross" @ 1159.
Apparently...this is the LR-to-RF "cross". How would you know which one?

If so.. I agree with your educated guesses as to corner loads.

If so... I would say there is considerable room for improvement ... whether you take Randy's model ( equal front weights) or my original "apportioned weight" model.... as a target.

- Wil

[Randy Blaylock]

Pat's question raised an issue that I remember being puzzled by for awhile, the two adjacent wheel sum question. It's not quite so black and white.

I did find that the weight sum between two adjacent wheels is not in fact always the same.

In real world situations, the axis line defining the centerline of the weight bias, either side to side, or front to rear, is almost never perpendicular or parallel to the lines making up the box connecting all the contact patches. There is no real way to know the exact orientation of the axis lines, the shift in bias beingthe only thing that suggests how much. Jacking one corner will transfer weight in varying degrees that do in fact make a very small percentage change in the fundamental weight distribution. It is subtle, but measurable.

[Wil Ferch]

Randy:

If so....it would have to be on a scale that would be over-shadowed by the other factors that we're trying to dial-in.

Recognizing that most folks will have a hard time with the "normal" ( let's say.."textbook") cases.....I would say we should not try to introduce this as typical, as it "bends the mind"....

If the sum of any side does not stay the same, then what is happening is that actual weight is being *moved within* the car..a completely different thing than trying to weight-jack or corner balance the weight that *already exists, un-movable* in a car..

Sure...it might happen but I would postulate that it's more of an anomaly...and it likely has numbers associated with it that are particularly small. Sure....not all cars are exactly "square" in two , 90 degree planes.

Man...others who are still having difficulty with the basic concept will get headaches after this !!!...

Wil