Suspension set up cheat sheet
12-09-2010, 04:11 PM
#61
Rennlist Member
Very clear to me. Here's a simple test. Take your iPhone (or something similar) and pretend it is the car. With the phone longways, hold each end with your thumb and forefinger on each corner. Lift up your thumbs, tilt it up on one side slightly to simulate a car leaning. Now gently lift the fore-finger that you imagine is outside rear corner. See how it immediately pressures the inside front, simulating wedge across the diagonal. This is what IMHO transfers load from the inside rear to the inside front, reducing grip in the back and increasing grip at the front.
I think Larry's example of using the phone is a good one, and one that someone should actually just film while discussing these and other theories. To be able to see in a very simplistic form would be a great 101 visual reference for 99% of us. Chuck it on Youtube and at least you can introduce the basics if not more complex theory.
So who's got the camera?
12-09-2010, 04:26 PM
#62
Scott...I am not saying that weight is actually transferred diagonally, it definitely IS NOT!
What I am saying is lets consider case A, with a certain front and rear roll stiffness. Then in a 1G corner we transfer a certain amount of load across the front axle, and a certain amount across the rear.
Now lets change the rear roll stiffness (make it stiffer), call it case B. Take the same corner, now we transfer more weight at the rear than before.
If we compare the corner weights between Case A and Case B, the weight across the diagonals is different.
Does that make sense?
What I am saying is lets consider case A, with a certain front and rear roll stiffness. Then in a 1G corner we transfer a certain amount of load across the front axle, and a certain amount across the rear.
Now lets change the rear roll stiffness (make it stiffer), call it case B. Take the same corner, now we transfer more weight at the rear than before.
If we compare the corner weights between Case A and Case B, the weight across the diagonals is different.
Does that make sense?
Scott
12-09-2010, 04:34 PM
#63
Let's say we have a car who's corner weights are
500 500
500 500
We are in some corner that transfers 500 lbs total, with equally stiff front and rear the corner weights would be (case A)
750 250
750 250
Now lets say we change the stiffness such that 80% weight trasnfer happens at the rear (or 400 lbs) (case B), corner weights are
600 400
900 100
And it is pretty clear that the front has a lot more grip and the rear a lot less in Case B...
12-09-2010, 04:39 PM
#65
I personally don't really like the idea of diagonal weight transfer either. It doesn't make much sense to me intuitively the same way I can think about taking a greater percentage of weight transfer at one end, thus less on the other end.
Let's say we have a car who's corner weights are
500 500
500 500
We are in some corner that transfers 500 lbs total, with equally stiff front and rear the corner weights would be (case A)
750 250
750 250
Now lets say we change the stiffness such that 80% weight trasnfer happens at the rear (or 400 lbs) (case B), corner weights are
600 400
900 100
And it is pretty clear that the front has a lot more grip and the rear a lot less in Case B...
Let's say we have a car who's corner weights are
500 500
500 500
We are in some corner that transfers 500 lbs total, with equally stiff front and rear the corner weights would be (case A)
750 250
750 250
Now lets say we change the stiffness such that 80% weight trasnfer happens at the rear (or 400 lbs) (case B), corner weights are
600 400
900 100
And it is pretty clear that the front has a lot more grip and the rear a lot less in Case B...
This is too funny. I just did almost exactly the same scenario as you. I changed the roll couple to 40/60 instead of 20/80.
It's only clear if you agree that the increased traction the lateral load provides does not overcome the reduced traction from the vertical load. You and I do....
Scott
12-09-2010, 04:49 PM
#66
Rennlist
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So from the example, as the roll rate is increased in the rear, some of the weight transfer (or vertical loading) has been transferred rearward on the outboard side and forward on the inboard side. And as Mark postulates, the diagonal weights will change drastically as the roll rate is increased on one end.
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Larry Herman
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Larry Herman
2016 Ford Transit Connect Titanium LWB
2018 Tesla Model 3 - Electricity can be fun!
Retired Club Racer & National PCA Instructor
Past Flames:
1994 RS America Club Racer
2004 GT3 Track Car
1984 911 Carrera Club Racer
1974 914/4 2.0 Track Car
CLICK HERE to see some of my ancient racing videos.
12-09-2010, 04:49 PM
#67
Lifetime Rennlist Member
I personally don't really like the idea of diagonal weight transfer either. It doesn't make much sense to me intuitively the same way I can think about taking a greater percentage of weight transfer at one end, thus less on the other end.
Let's say we have a car who's corner weights are
500 500
500 500
We are in some corner that transfers 500 lbs total, with equally stiff front and rear the corner weights would be (case A)
750 250
750 250
Now lets say we change the stiffness such that 80% weight trasnfer happens at the rear (or 400 lbs) (case B), corner weights are
600 400
900 100
And it is pretty clear that the front has a lot more grip and the rear a lot less in Case B...
Let's say we have a car who's corner weights are
500 500
500 500
We are in some corner that transfers 500 lbs total, with equally stiff front and rear the corner weights would be (case A)
750 250
750 250
Now lets say we change the stiffness such that 80% weight trasnfer happens at the rear (or 400 lbs) (case B), corner weights are
600 400
900 100
And it is pretty clear that the front has a lot more grip and the rear a lot less in Case B...
claykos,
This is too funny. I just did almost exactly the same scenario as you. I changed the roll couple to 40/60 instead of 20/80.
It's only clear if you agree that the increased traction the lateral load provides does not overcome the reduced traction from the vertical load. You and I do....
Scott
This is too funny. I just did almost exactly the same scenario as you. I changed the roll couple to 40/60 instead of 20/80.
It's only clear if you agree that the increased traction the lateral load provides does not overcome the reduced traction from the vertical load. You and I do....
Scott
Case B is either a drift car or a big crash.
12-09-2010, 05:46 PM
#68
Look at the cross weights. Case A is 50% while case B is 65%. It is widely understood that when corner balancing a car, it is far more important to get good cross weights than side to side. I don' disagree that the increased load on the tire has an impact, I still stand by my belief that the change in cross weight (load) is the much bigger impact to handling.
You can't compare the static corner balance of car to what is happening dynamically when changing roll couple. At least not as long as you change the wheel rates evenly on the axle.
In the example provided by claykos, the car will corner the same in left hand and right hand turns.
Using wedge affects the static corner balance of a car and will cause a car to behave differently in in left hand and right hand turns.
Scott
12-09-2010, 06:01 PM
#69
Lifetime Rennlist Member
Why do you want the cross weights the same on a road race car? So the car corners with the same characteristics in both left hand and right hand turns. Why is this important? Otherwise changes to the setup will be different for left hand turns compared to right hand turns. If the car steers perfect in right hand turns but understeers in left hand turns, fixing the left hand turning will cause oversteer in right hand turns.
You can't compare the static corner balance of car to what is happening dynamically when changing roll couple. At least not as long as you change the wheel rates evenly on the axle.
In the example provided by claykos, the car will corner the same in left hand and right hand turns.
Using wedge affects the static corner balance of a car and will cause a car to behave differently in in left hand and right hand turns.
Scott
You can't compare the static corner balance of car to what is happening dynamically when changing roll couple. At least not as long as you change the wheel rates evenly on the axle.
In the example provided by claykos, the car will corner the same in left hand and right hand turns.
Using wedge affects the static corner balance of a car and will cause a car to behave differently in in left hand and right hand turns.
Scott
12-09-2010, 06:06 PM
#70
Rennlist Member
12-09-2010, 06:18 PM
#71
12-09-2010, 06:42 PM
#72
In a dynamic sense, wedge (asymmetrical static cross weights) causes a car to corner differently in right hand than it does in left hand turns. Right?
How does this relate to changing roll couple symmetrically?
In claykos' exaggerated example , if the roll couple is not 50/50, the corner weights (in the corner) are not symmetrical on either side. That is the desired result of altering roll couple: so that it is possible to tune handling characteristics.
Scott
12-09-2010, 06:50 PM
#73
Rennlist Member
Look at the cross weights. Case A is 50% while case B is 65%. It is widely understood that when corner balancing a car, it is far more important to get good cross weights than side to side. I don' disagree that the increased load on the tire has an impact, I still stand by my belief that the change in cross weight (load) is the much bigger impact to handling.
Case B is either a drift car or a big crash.
Case B is either a drift car or a big crash.
12-09-2010, 06:57 PM
#74
No, your example shows that no weight has been transferred diagonally, effectively or otherwise. What it shows is that less weight is transferred from the right to left at the front in a right hand turn when the rear is stiffened.
More weight is on the RF-LR diagonal, but no weight transferred along the diagonal. This is a not so subtle difference.
Scott
12-09-2010, 07:06 PM
#75
Now that I have had a chance to look at the math...
No, your example shows that no weight has been transferred diagonally, effectively or otherwise. What it shows is that less weight is transferred from the right to left at the front in a right hand turn when the rear is stiffened.
More weight is on the RF-LR diagonal, but no weight transferred along the diagonal. This is a not so subtle difference.
Scott
No, your example shows that no weight has been transferred diagonally, effectively or otherwise. What it shows is that less weight is transferred from the right to left at the front in a right hand turn when the rear is stiffened.
More weight is on the RF-LR diagonal, but no weight transferred along the diagonal. This is a not so subtle difference.
Scott
I fully agree with you and thought more about it myself. I do not see diagonal weight transfer either. But the car is effectively "wedged" differently in each case. But it is due to increased weight transfer between LF-RR and decreased between LF-RF.....