Technical Lowering Question
#1
07-12-2005 | 05:59 PM
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Technical Lowering Question
Just had tt lowered with PSS9. I am very detailed and noticed the front left was almost 1/4 inch lower than right front. I called the guy at shop and he claimed this was because to corner balance the car properly for track. Then I said I thought porsche designs car to be even on both sides, but he then said with driver in the car weight is uneven. I still do not get it; and the guy sounded like he knew his stuff. Does this make sense or did they mess up?
Dan
Dan
#2
07-12-2005 | 06:11 PM
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did u tell him to corner balance the car if u're not going to track it all all? IMO u just need a perfect alignment rather than the corner balance. btw, if ur weight is going to change the height of the car why is the driver side is lower than the passanger side since ur weight is on the left all the time?
#3
07-12-2005 | 06:37 PM
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Arling, thats exactly what I was thinking. The car was just aligned but I told them I would corner balance later because of some weight issues with custom stereo. So they said the car was set lower in the front left because it would have to be when corner balanced. Any other opinion? It would make more sense to lower front right more because weight is going on left side.
#5
07-12-2005 | 06:50 PM
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Arling, seriously consider starting up a shop in Chicago, the local 6speed people could probably keep it going. It is tough to find a good shop with reasonable prices. There are a few top notch shops but they see a turbo and go crazy with bill!!!!
#6
07-12-2005 | 07:27 PM
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Well if he did a corner balance what are the cross weights?
What did he set the car up for ?
This will determine what he did.
When you say they did a track set up? What exactly did they do?
What did he set the car up for ?
This will determine what he did.
When you say they did a track set up? What exactly did they do?
#7
07-12-2005 | 10:42 PM
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#9
07-13-2005 | 08:59 AM
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dlm,
I echo BentleyNPB's comments. Obtain the cross weighting results from the shop as well as the individual corner weights.
As a matter of point, corner weighting does not correlate completely to the ride height uniformity at each of the four corners, or, more specifically, between the two front corners and between the two rear corners.
Corner weighting's purpose is to insure, through varying degrees of spring preload, that the two front corners are applying the same (or a chosen percentage as he supposedly explained to you) loads to the ground with the car at rest. The same holds true for the rears. The additional function of the corner weighting process is to insure that the cross weights are relatively equal as well. What I mean by this is that the summation of the front left and rear right approximately equals the summation of the front right and rear left. Cross weighting as it is called.
THe benefit of corner weighting is that the car's response will be the same, or nearly the same, when turning it left or right since the springs are "balanced" to begin with.
As a counterpoint to illustrate what I am talking about...consider this....
If you were to remove the spring at your left front wheel and keep the one at the right front wheel, the 911 would (might) stay statically upright due to the rear engine design. I am not sure this would actually happen, but I think you can visualize that for my example. So, to the onlooker, they would simply see a car with 4 wheels on the ground. The car, however, would not function properly in right hand turns.
THat is an extreme (albeit bad) example of why corner balancing is done.
Now, another point. In my opinion, given the ability level of 90% of the drivers here and everywhere, I think corner balancing is a waste of time considering the price they charge to do it. I know, I will probably get flamed for that comment, BUT, those flames will undoubtedly come from the 10% of good drivers out there!!! POINT MADE!!!
I have run my car both ways......ride height equivalency from side to side of the car and corner balanced. Frankly, there is barely an imperceptible difference and I have done alot of track days.
So, in conclusion, I would absolutely try to understand this theory, take your head out of the sand (not meant in a bad way) and collect both your alignment data and corner balance data from your shop so you can understand what was done, what the numbers are and how all of it affects the handling of your car.
Good luck!!
I echo BentleyNPB's comments. Obtain the cross weighting results from the shop as well as the individual corner weights.
As a matter of point, corner weighting does not correlate completely to the ride height uniformity at each of the four corners, or, more specifically, between the two front corners and between the two rear corners.
Corner weighting's purpose is to insure, through varying degrees of spring preload, that the two front corners are applying the same (or a chosen percentage as he supposedly explained to you) loads to the ground with the car at rest. The same holds true for the rears. The additional function of the corner weighting process is to insure that the cross weights are relatively equal as well. What I mean by this is that the summation of the front left and rear right approximately equals the summation of the front right and rear left. Cross weighting as it is called.
THe benefit of corner weighting is that the car's response will be the same, or nearly the same, when turning it left or right since the springs are "balanced" to begin with.
As a counterpoint to illustrate what I am talking about...consider this....
If you were to remove the spring at your left front wheel and keep the one at the right front wheel, the 911 would (might) stay statically upright due to the rear engine design. I am not sure this would actually happen, but I think you can visualize that for my example. So, to the onlooker, they would simply see a car with 4 wheels on the ground. The car, however, would not function properly in right hand turns.
THat is an extreme (albeit bad) example of why corner balancing is done.
Now, another point. In my opinion, given the ability level of 90% of the drivers here and everywhere, I think corner balancing is a waste of time considering the price they charge to do it. I know, I will probably get flamed for that comment, BUT, those flames will undoubtedly come from the 10% of good drivers out there!!! POINT MADE!!!
I have run my car both ways......ride height equivalency from side to side of the car and corner balanced. Frankly, there is barely an imperceptible difference and I have done alot of track days.
So, in conclusion, I would absolutely try to understand this theory, take your head out of the sand (not meant in a bad way) and collect both your alignment data and corner balance data from your shop so you can understand what was done, what the numbers are and how all of it affects the handling of your car.
Good luck!!
#10
07-13-2005 | 09:12 AM
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One more thing.....
I went through an analysis a while back regarding the effects of a driver in the car on the corner weights. I will briefly recap here...ready for some algebra????
Assume the driver is 200 pounds (nice round number). Assum that the driver is positioned 1/2 way between the front and rear wheels (fore aft). Therefore, 100 pounds of his weight goes to the rear wheels and 100 pounds of his weight goes to the front wheels.
Now, since the car is roughly symmetrical about its centerline, the left wheels will pick up 2x the weight of the right wheels.
For the rear two wheels, or the front two wheels....
L = 2R
and, as we said earlier......
R + L = 100
substituting....
2R + R = 100
or
3R = 100
or
R = 100/3 = 33.33 pounds
L = 2R = 66.66 pounds
So the left front wheel and the left rear wheel will experience a load increase of 66.66 pounds
and
The right front wheel and the right rear wheel will experience a load increase of 33.33 pounds.
Therefore, and conversely, relative to corner balancing, the rights, at rest, without anyone in the car, should be 66.66 pounds more, each, than the left wheels.
Get it?
I went through an analysis a while back regarding the effects of a driver in the car on the corner weights. I will briefly recap here...ready for some algebra????
Assume the driver is 200 pounds (nice round number). Assum that the driver is positioned 1/2 way between the front and rear wheels (fore aft). Therefore, 100 pounds of his weight goes to the rear wheels and 100 pounds of his weight goes to the front wheels.
Now, since the car is roughly symmetrical about its centerline, the left wheels will pick up 2x the weight of the right wheels.
For the rear two wheels, or the front two wheels....
L = 2R
and, as we said earlier......
R + L = 100
substituting....
2R + R = 100
or
3R = 100
or
R = 100/3 = 33.33 pounds
L = 2R = 66.66 pounds
So the left front wheel and the left rear wheel will experience a load increase of 66.66 pounds
and
The right front wheel and the right rear wheel will experience a load increase of 33.33 pounds.
Therefore, and conversely, relative to corner balancing, the rights, at rest, without anyone in the car, should be 66.66 pounds more, each, than the left wheels.
Get it?
#12
07-13-2005 | 10:57 AM
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Re: Technical Lowering Question
Originally posted by dlm477
Just had tt lowered with PSS9. I am very detailed and noticed the front left was almost 1/4 inch lower than right front. I called the guy at shop and he claimed this was because to corner balance the car properly for track. Then I said I thought porsche designs car to be even on both sides, but he then said with driver in the car weight is uneven. I still do not get it; and the guy sounded like he knew his stuff. Does this make sense or did they mess up?
Dan
Just had tt lowered with PSS9. I am very detailed and noticed the front left was almost 1/4 inch lower than right front. I called the guy at shop and he claimed this was because to corner balance the car properly for track. Then I said I thought porsche designs car to be even on both sides, but he then said with driver in the car weight is uneven. I still do not get it; and the guy sounded like he knew his stuff. Does this make sense or did they mess up?
Dan
Cheers,
#13
07-13-2005 | 11:01 AM
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KPV, Although your algebra is correct, there are some flaws in your model:
1. Your conclusion invalidates your basic assumptions. That is once you change the settings as you conclude you actually change the basic assumption of equal distribution of (driver) weight and symmetry. Therefore the conclusion you draw is probably an over adjustment! (I need some time to work out the appropriate differential equation).
2. Your model totally disregards variance. That is, your model is only good on average (head in the oven, feet in the freezer..on average correct temperature). Lets say there is variation in the spring tension, mass distribution, measurement systems, tire pressure, tire balance,...(you get the point). Once again these variance components could render your "average" model irrelevant.
1. Your conclusion invalidates your basic assumptions. That is once you change the settings as you conclude you actually change the basic assumption of equal distribution of (driver) weight and symmetry. Therefore the conclusion you draw is probably an over adjustment! (I need some time to work out the appropriate differential equation).
2. Your model totally disregards variance. That is, your model is only good on average (head in the oven, feet in the freezer..on average correct temperature). Lets say there is variation in the spring tension, mass distribution, measurement systems, tire pressure, tire balance,...(you get the point). Once again these variance components could render your "average" model irrelevant.
