I have been taking my corner weights for an RS America at the last few events but I'm not sure how to interpret them. Is their a "correct" ratio I should be looking for or is it all tied into the rest of my suspension setup?

 

F/R is dictated by the car, with the ability to shift a little with height. However, height can be used to tune handling and should not be used to try to hit a targer weight. L/R is a function of design and the fact that you sit on one side, so you can not really tweak this.

What you care about is cross weight. LF+RR vs RF+LR. You want this as close to 50/50 as possible unless you are intentionaly jacking weight. Most electronic scales will give you this % as a direct read out. Assuming nothing is way out of whack with the frame/suspension, a balanced cross weight will give you the best handling.

 

As a follow-up question, I recently had an alignment and corner-balance done. All appeared to be well. Then, several weeks later, I noticed that my front right was significantly (~1.5") lower than the front left. Hmmm. Then I went to the back of the car. Guess what? Just the opposite!!! The rear LEFT was significantly lower than the rear right!

What is going on here?

I'm going to take the car back to the alignment shop to be re-checked, but thought that someone might have an idea of what may have happened.

Thanks.
Erick

 

Erick,

If your chassis is straight, that is not really possible. I suspect you were not on a level spot. If you lower the RF, then the car has to tilt and the LR will be higher unless the chassis has so much flex that it can twist that much (I don't think any recent 911 should twist that much).

Find a spot that is level across all 4 corners of the car, then you need to bounce each cornet to settle the suspension. Then you can get a good measure but you really need to do that from the official measurment points.

 

One point to note about corner weights that Mark Eluded to.

You need to be on flat level ground. If you are taking corner weight at a set of scales at a track the portable it is likely that the ground is not perfectly level and your corner weights will not be right. You must have a level surface.

 

You're right... doesn't make sense. I'll be in the shop on Thursday and will report back with my findings.
Erick

 

I have seem many older 911's (mid-80's vintage) that when corner balanced correctly had different fender heights. This is why the factory specifies where you measure the ride height from. You measure from points on the chasiss not the body. Your car may be perfect.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by M758:
<strong>One point to note about corner weights that Mark Eluded to.

You need to be on flat level ground. If you are taking corner weight at a set of scales at a track the portable it is likely that the ground is not perfectly level and your corner weights will not be right. You must have a level surface.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">You can get away with quite a bit of error IF it is in the right direction. The four corners must be square so there is no twist on the frame (this is the most important). Then the side to side must be lever across the front and the rear.

If it is off front to rear, the impact is very, very small. If you do that math and back that up with measuring, you can see that will only induce and error of a few lbs. Many garage floors (like mine) are square and level side-to-side but slope for drainage. This is still a good set up space.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Radical Racer:
<strong>L/R is a function of design and the fact that you sit on one side, so you can not really tweak this.

What you care about is cross weight. LF+RR vs RF+LR.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Actually, Mark, balancing the diagonals will not be correct if L/R weight distribution is not 50/50 on the car (which usually only happens in center-seaters). It will be close, possibly even close enough for practical purposes, depending on how different the left side weight is compared to the right, but the perfect corner balance formula is to have LF/LR=RF/RR.

TT

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Tom Tweed:
<strong>Actually, Mark, balancing the diagonals will not be correct if L/R weight distribution is not 50/50 on the car (which usually only happens in center-seaters). It will be close, possibly even close enough for practical purposes, depending on how different the left side weight is compared to the right, but the perfect corner balance formula is to have LF/LR=RF/RR.

TT</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">What I meant, but did not say real clearly, is that you do not try to balance the car L/R as part of the corner balance. You balance it across the diagonal. From there, L/R will likely be close. In theory, L/R can still be way off, but it is not likely to happen in a decently designed and straight car. As an exteme example, consider a car that is LF/RF/LR/RR 100/500/100/500. The diagonal balance is perfect but the L/R is not. You would not get something that extreme in the real world, but the same car at 275/325/275/325 is perfect cross but not L/R balanced.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Radical Racer:
<strong>[QUOTE]

is that you do not try to balance the car L/R as part of the corner balance. You balance it across the diagonal. From there, L/R will likely be close. </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Mark,

That is the way we corner balance my 993. But on Larry Schumacher's LOLA SRPII car he ran in Grand AM a few years back, my mechanic said the car was much better when they got the left to right weight almost perfect and close on the cross weights. FWIW.

My mechanic doesn't want to see a 100lbs off side to side in the front either but anything within 30-40 lbs is probably acceptable.

 

Interesting Greg. I may have to try that and see if I can feel any difference. Thanks.

 

Mark,
To clarify. They made sure the left front and the right front where equal, not the whole left side and right side. Not sure if that was clear or not in my previous post.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Greg Fishman:
<strong>Mark,
To clarify. They made sure the left front and the right front where equal, not the whole left side and right side. Not sure if that was clear or not in my previous post.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Thanks - that was not clear but I understand. I will at least try that next time I corner balance and see how far off everything else is.

 

My mechanic (Mike Callas) does the corner balance as described by Mark. On the diagonals and as close to 50% distribution. My car is somewhere at 49.3% for reference. Something important that is not mentioned here is the need to have the driver in the driver seat and the car in "racing trim" with the average fuel on, tires etc when the corner balance takes place.
My mechanic is very adamant that a setup that works with me inside the car will not work for someone who is not a similar weight with me. I'm very heavy weight (250lbs) and the corners in ride height are posting different measurements without me in the car to as much as 3/4 of an inch difference.
With so much racing experience on his belt I have no doubts in my mind that this is the way to go.