Stiff springs - more or less grip?
#76
The main problem with variable rate springs is that they eat up valuable suspension travel. Yes, the idea of having a soft initial rate for a supple chassis to soak up a rough road surface and then transitioning to a main stiff rate that can handle the weight transfer at full “g” cornering is appealing.
If the car has enough travel to spare, then it's ok, but if not, then it will end up riding on the bump stops. Once on the bump stops, that corner, probably the outside front, will turn effectively into an inappropriately stiff spring, and that corner will wash out, i.e. the car will push like a pig.
Having said that, I'm currently working on designing a dual rate spring combo for my 951. I’m on my 2nd prototype and it seems to be working to expectations. I just have to work out a few more bugs before I call it a done deal.
If the car has enough travel to spare, then it's ok, but if not, then it will end up riding on the bump stops. Once on the bump stops, that corner, probably the outside front, will turn effectively into an inappropriately stiff spring, and that corner will wash out, i.e. the car will push like a pig.
Having said that, I'm currently working on designing a dual rate spring combo for my 951. I’m on my 2nd prototype and it seems to be working to expectations. I just have to work out a few more bugs before I call it a done deal.
#77
Race Car
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Ok back to the simple stuff, I think we all for the most part know how compression damping relates front to back. If you understeer (all other suspension being equal) then you want to soften the front and/or stiffen the back. Either way creating a higher ratio of stiffness in the back compared to the front. And vice versa for oversteer, A little stiffer in the front and softer in the back to induce a bit of understeer.
We've talked about rebound in various ways as directed straight towards handling, but how does front and rear rebound relate to each other. And in what areas will you see it? ALL ELSE BEING EQUAL ON THE SAME CAR WHILE TUNING IT.
So how does changing ratio of front to back rebound damping affect the handling on the car???
We've talked about rebound in various ways as directed straight towards handling, but how does front and rear rebound relate to each other. And in what areas will you see it? ALL ELSE BEING EQUAL ON THE SAME CAR WHILE TUNING IT.
So how does changing ratio of front to back rebound damping affect the handling on the car???
#78
Here is something interesting. In 2004 Porsche redesigned the suspension for the 996 RSR. They fixed all the suspension geometry which allowed the car to run above-the-ground roll centers for the first time. (Previous to this the GT cars had severely lowered street suspension, which put the roll centers well below the ground, which caused a pretty big increase in roll). These mods should have allowed Porsche to run much softer springs to achieve the same roll gradient. They ran the same old stiff (as high as 2150 lbs/in) springs anyway. Evidently they felt that the higher roll centers and stiff springs were both beneficial.
Chris Cervelli
Spline Technologies
I have made recent changes in several areas and they, as yet, are untested. I changed dampers, springs, tires and added a significant amount of front and rear adjustable downforce. I'm trying to gain more understanding with several suspension topics before a test day (excuse me, driver orientation day) I am attending at Road Atlanta next Friday. I hope to learn more about what to change when the car does whatever its going to do. This whole RC/CG rolling moment issue is one I can't find a satisfactory explanation for in any of my reading material. The Millikens and Carroll Smith explain definitions in an understandable way but no specific answer to what I posed above.
#79
As I understand it, the distance between the roll center and the car’s center of gravity is the “leverage arm” that acts on the chassis to make it roll upon turn entry.
Since the car’s center of gravity is always above ground, then having roll centers below ground level only serve to increase the length of this “leverage arm.”
Since the car’s center of gravity is always above ground, then having roll centers below ground level only serve to increase the length of this “leverage arm.”
#80
As I understand it, the distance between the roll center and the car’s center of gravity is the “leverage arm” that acts on the chassis to make it roll upon turn entry.
Since the car’s center of gravity is always above ground, then having roll centers below ground level only serve to increase the length of this “leverage arm.”
Since the car’s center of gravity is always above ground, then having roll centers below ground level only serve to increase the length of this “leverage arm.”
Last edited by Accelerator; 02-27-2009 at 03:54 PM.
#81
I guess your question then really comes down to, “which is the worst of two evils: 1) reduction in overall traction due to “jacking effect” i.e. lifting both inside wheels, or 2) reduction in overall traction due to excessive chassis roll (i.e. too much weight transfer on a given pair of wheels).”
I’d say the jacking effect is worse, so in your case, lower CG is better.
I’d say the jacking effect is worse, so in your case, lower CG is better.