corner balance

[1974nine11]

I' m getting ready to have my '74 911 corner balanced, could someone please elaborate what that procedure exactly is ? and how much should one expect to pay ? any input would be appreciated

[Formerly Steve Wilkinson]

I have no idea what it costs, having only done it myself, but I find the easiest way to explain corner balancing is to imagine you're sitting on a big, four-legged chair. First time you climb into it, only two of the legs are actually touching the floor, so the thing sort of rocks back and forth because there's a quarter-inch gap between floor and leg on two of the legs. You need to adjust the length of all four of the chair-legs so they're touching the floor equally, and are doing so with you sitting over to the left side of the chair, which is where you like to watch TV, like you would be if you were in the driver's seat of a car.

Where this becomes tricky is that imagine the tippy-two-legs chair, and it becomes obvious that you could simply screw away on the adjustment of one of the two short legs and get the chair stable, all four legs touching the floor. But the chair probably wouldn't be level. What you need to accomplish is to adjust the chair legs so that ultimately the chair is perfectly level (with you sitting where you normally do to watch TV) and that each of the four legs is exerting the identical pressure on the floor.

Trickier yet: Maybe you don't want identical pressure on all four legs but some differential front-to-rear or even side-to-side that you have predetermined will make your, uh, chair handle better.

That's corner-balancing. Not easy.

[cashflyer]

I had my SC corner balanced earlier this week. $88

[TechnoViking]

Corner balancing just takes time. It's done by adjusting the height of each wheel until the weight is where you want it. I think most recomend a 60/40 split rear to front, equal weight left to right, ideally with you or someone who weighs what you do in the car.

You'll get charged an hourly rate, and you need to find a shop that has a set of scales. If you are not adjusting the height, and you shop knows what they are doing, they should be able to get it pretty close in an hour or two.

It does not need to be perfect for most driving. Frankly, if it is a street car, and you are not flat-spotting tires coming to a stop, I wouldn't even bother.

I do my own for my race car. It can me maddening until you figure out a few things. If you want to do your own, search for "tripod" and balancing. I do mine without scales and it's fine for racing.

I'd also recommend a pad and paper. Write down each adjustment you make so you aren't going around in circles.

[Wil Ferch]

Sorry to say...here's where Bkreigsr is all wrong....

A surprise to many...but the TOTAL of ANY TWO ADJACENT wheels will ALWAYS ( ! ) stay the same...whether you've got great or terrible corner balance. If you have 40/60 fr to rear weight distribution, that's what you'll ALWAYS have (unless you move stuff...like the battery from one place to another, within the car). If you have 51/49 left-to-right weight distribution...you will ALWAYS have that too ( BTW...it will bias a bit to the left because all the steering gear and steering wheel and battery, and such.... are more to the left on non-Brit cars). So, you won't hardly ever get perfect left-to-right equality for ALL FOUR corners. So...any two adjacent wheels will sum up to the same total. The drill is this, if you alter one corner of the car ( say, heavier), then the opposite diagonal will experience the same effect. RF corner went up 20 lbs?.....then so does the LR. Surprisingly....the front TWO wheels sum up the same value and the BACK TWO wheels will sum up to the same total they had before ( as would LF+LR...or LR+RR...or RR+RF..or RF+LF). Any two adjacent wheels sum up the same..always..unless you actually move mass around in the car.

Look at a lengthy exchange by a number of people including myself and Randy Blaylock ( where we first disagree on some fine points but then I've come to realize a new nuance later in the discussion)...look at the archives. It's not a simple subject, but some parts are simply fundamental and inviolate.

[richde]

Can a car only be balanced if, for example, it didn't have the 1/2 inch difference in fender height from front to rear? Or is it totally independent of ride height?

[wnsgc]

I just had my 85 Targa corner balanced and aligned for $250 - in central New Jersey.

This was done right after I had turbo tie rods installed as well as new torsion bars, poly-graphite bushings and the car lowered to a tad-below european road height.

End result: Simply amazing!

[Wil Ferch]

no offense intended, bkreigsr
...have a great Easter Holiday !

[cgarr]

What will the rake change?

[Gunter]

Originally Posted by 1974nine11

I' m getting ready to have my '74 911 corner balanced, could someone please elaborate what that procedure exactly is ? and how much should one expect to pay ? any input would be appreciated

Cost is relative to what needs to be done.
Read and study some more before you go, lots of info here.
Cornerbalance is done in conjunction with alignment and adjusting ride height.
Before anything, all components like shocks, struts, balljoints, tierods, bushings etc. need to be checked and replaced if necessary.
Most likely, the main bushings in the trailing arms (Springplates) need to be installed and you may want the bump-steer kit (Spacers under the rack)
You have to decide on ride height; what setting do you want?
Next is alignment:
Alignment shops have the factory settings in their computer, which most people don't want.
What Camber and Toe do you want on the 4 wheels?

Defective components will show up during alignment and a good shop will tell you what needs to be replaced. (Which adds to the cost)

Study some more; do a search here. It's been covered many times.

[Wil Ferch]

Since I may have inadvertantly offended bkreigsr or others....let me at least describe a Cliff's note version of this whole mess. ( although it ends up a bit long...can't help that).

Our cars have the major mass components located within certain areas of the car...and this means the "two-adjacent-wheel" total weight (rule) will always be the same. For example, our cars are typically 40/60 front to rear weight distribution, and no amount of weight jacking or corner balancing will alter that.

Let's use a test case....

original weights
LF 550 RF 530
LR 830 RR 860

total weight is 2770. fr/rr balance is 39%/61%

Lets "jack-in" some weight on the RF corner..and "add" (say) 20 lbs. Notice, we're not really adding mass like a brick of lead, we're simply ( for example) raising the RF corner height so it will "press" down more on that corner by 20 lbs.

What happens? This happens ---> the RF will add 20 lbs but so will the opposite diagonal. Let's do the math.....remembering that ANY TWO ADJACENT wheels must add up to the same amount.

New numbers
LF 530 RF 550
LR 850 RR 840

Notice that the RF went up 20 lbs ( original intent) and that its diagonal... the LR.... went up 20 lbs from before, too. The TOTAL front weight of the car must remain unchanged, so to get the same FRONT TOTAL of 1080 ( as before)...then the LF must compensate by coming down 20 lbs. However, remember that whatever happens on one corner also happens on * its * diagonal. So, if the LF compensated by going down 20 lbs...so did the RR. It also went down 20 lbs.

So...what do we have? Same total weight ( 2770 lbs). Same front weight ( 1080 lbs). Same rear weight ( 1690 lbs). Same fr/rr distribution ( 39/61). Also, same total left-to-right distribution. Etc. BUT..... each CORNER is now carrying a different weight.

So ...we can see what a diabolical tail-chasing game this all becomes !

If this result is undesired and too big of a change, then maybe what we wanted was only to add 10 lbs (to start) on the RF...instead of 20 lbs...and we do the whole thing over again. In this case, the new numbers are--->

LF 540 RF 540
LR 840 RR 850

These seem to be "better" corner balance numbers..as the four corners are each carrying a more equal weight compared to their sideways-neighbor than before. But...we're still not done...here's where I had the epiphany in my dialogue with Randy Blaylock in the other thread.

Bear with me on this --->

The "pure" idea of corner weighting is to apportion each corner of the car with the weight it SHOULD have...based on where the heavy masses are located. If the steering hardware and battery (in the LF fender) make the LF a bit heavier altogether...then the "ideal" corner balance would be if the LF actually...in fact...carried a bit more weight than thr RF. These are not symmetrical Formula 1 cars, the weights are in odd places...so the "ideal" is not to have each corner carry the equall weight of its sideways-neighbor.

OK...that was my argument in the Blaylock thread and it's still valid. HOWEVER....from a PRACTICAL point of view.....what happens under heavy braking is more important than if the car turns-right or turns-left the same way ( if perfectly corner balanced).

So.....although most 911's *should* have a slight LF weight bias...if you ( instead), purposely "weight-jack" the car to show IDENTICAL front left and right weights.....the car will NOT be perfectly corner-balanced...but it would NOT tend to lock up one wheel under heavy braking. Negatives?..Yes !....you've now introduced a "weight jacking" to the car ( the corners are NOT apportioned their appropriate weight; perfect corner balancing is now compromised)...and the car will behave slightly different in left-to-to-right turns ( the whole point of corner-balancing). BUT...the trade-off for better braking is usually a better deal than trying to achieve "perfect" corner balance...since one-wheel locking of brakes is more of a problem than how much steering angle you dial in for that perfect corner balance....


Makes sense ..????

Easy peesy stuff...eh ??

[kent olsen]

If you don't have the adjustable spring plates in the rear how can they corner balance the car?

Are they just adjusting the fronts with those height adjustors in the front suspension?

I thought to adjust the rear you had to pull and reindex the rear swing arm on the torsion bar, which has always sounded like a lot of work.

[Wil Ferch]

Kent:
That's right..major PITA
If you don't have the adjustable spring plates, you make-do with the front adjusters. If you're lucky, that's all you'll need. If not, you will either achieve your corner balance target ( but your ride height is all screwed up)...OR... you will need to re-index the rear spring plates...PITA.

[Wil Ferch]

rake will not change front/rear bias to any meaningful degree...... since you didn't move any weight ( mass) from one positon of the car from another. Sure, removing bumpers or changing exhausts will...since you're changing the weight.

[burgermeister]

Wil, regarding your "point 2" up above - I thought the idea of corner balancing was to split the weight of each axle as equally as possible for each tire. The lateral force capability of an axle (both sets of tires at either end of the car) is greatest when both tires are equally loaded. When one tire carries more load than the other, the combined lateral force capability of the axle goes down. This is because the vertical load - max lateral load curve for a tire is not linear.

Now, during cornering, weight transfer will occur - no way around it. If a car is unbalanced left-to-right on one axle (and therefore unbalanced the opposite way on the other axle) , the maximum lateral force capability of one axle will be better for a left turn (at the same time, the other axle will be worse), and vice-versa. In other words, if you were way off on the balance and everything else was just at the ragged edge, the car could push at the limit for a LH turn, and spin at the limit for a RH turn (or vice-versa). I think this behaviour is used to tune the push / spin balance with the sway bars (which will shift the lateral weight transfer, and therefore the first axle to loose traction during cornering, to the front or rear axle, depending on which has the greater roll stiffness).

Of course, given the unequal weight distribution of the car, a perfect corner balance may be impossible to achieve - in which case I'd let the rear axle be equal, and the front axle be different, given that I prefer the front end coming loose first ... so, to end a long diatribe, is this what you are referring to?

I'm in the process of reading the Milliken book, and I have no experience whatsoever, so I know just enough to possibly sound competent but be a danger to myself and others - feel free to comment and correct!

[Wil Ferch]

burgermeister:

This is a complicated topic and many do not want to expend the energy to fully understand what's going on. This is not a slam on anyone... but there are many nuances that are easily missed, and you have to get your mind fully around the issues.

To your questions ... yes .. if you read the latter half of my long text .. I am openly admitting that I would be willing to compromise "perfect" corner balance.....to instead try to achieve a purposeful front "weight jacking"... where the new target is to get equal front weights.

Why ?.....

Because for most of us... especially for track use....it is really spooky to have "perfect" corner balance ( with unequal LF and RF weights, because the car actual weights are not equal left-to-right)...and then find yourself with really bad thresh-hold braking. One of the front tires will then always lock up first because to get "perfect" corner balance...you "properly" loaded up the two front tires unequally to match where the front masses are located ( i.e...unequally)

Instead...IMHO.... a better "compromise" is to target equal front weights...to gain better threshold braking characteristics....at the expense of less-ideal "corner balance". What usually occurs when you gain equal fronts is that the rears are slightly out of whack ( from a "perfect" corner balance standpoint). This then... makes the car behave slightly differently in left-to right turns...as you so correctly point out....but not THAT much of a difference to make a real difference....if you get things close.

So...there are many therories or "targets" you may strive for...but I like this "equal-front" approach.... and this is the basis for my longish dialogue with Randy Blaylock...avid racer. I was converted to his view, which is this same equal-front theory.

EDIT---> if people like reading up on this stuff, here is a link with further embedded links...be prepared, sit down with a large cup of coffee and a note pad --> Critique Specs for the Alignment Shop

[hcoles]

Wil, I like this discussion.
I think I follow...with the equal front approach you get more even threshold braking.
With the equal per the center of mass approach you get theoretically same turn right or turn left behaviour.
Am I getting what you are saying?
Maybe the pratical target is to be somewhere in between... say 80% on that scale between equal fronts and mass approach... where the 80% is close to the equal fronts.
Also I think your correct... locking a wheel on braking on the track is very noticable...turn right and turn left understeer/oversteer doesn't seem to be too noticable.... but might add into the equation of a "perfect" for a given track weight balance.

[hcoles]

at the risk of throwing a wrench in the works......
let's look at threshold braking...and think e.g. that all the weight is now on the fronts.
if the mass of the car is not centered across the fronts you would want one front to be able to generate more force than the other to avoid the car from turning.. right?

[kent olsen]

To roll another stone down this hill.

Like the circle track junkies who always turn left, our tracks predominately trun right so when considering car setup right turning becomes important as well.

[Wil Ferch]

It comes down to this...and this is not gospel.... but simply one man's opinion if you consider the magnitude of the numbers that are involved, and where we're discussing them.

Grossly out of balance cars are dangerous to drive fast. Those that have 50-100 lbs (say) disproportionatley loaded from where they should be. A real corner balance "mess". We're not talking about these cars I hope. We're talking about a finer cut to the question.

A "perfect" corner balance for a tin-can car ( not a symmetircal formula car)...might get you to within 5-40 lbs of "correct" weight ( whatever that is)..at each corner.

So....My point is that for threshold braking....a difference of 40-50 lbs from "what it should be" at any one of the front corners can be felt immediately....it can make one brake lock up prematurely.

However, from a "cornering" standpoint.... when we're talking values of 550 lbs or 830 lbs on each corner...as a starting point..... then being "off" by 5-22 or 5-40 lbs might not be such a big deal, especially if the "non-ideal" weights occurs on the "rear-heavy" cars we love so much. It is the rears that get "slightly" out of whack if we target equal fronts...and the amount the rears end up being "off" might be tens-of-pounds only. Altogether...in my view...this is a good trade-off between cornering behaviour and braking behaviour on a car.

hcoles ...yes .... I think you summed it up nicely.