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Lets talk about the "Falling Effect"

4032 Views 3 Replies 3 Participants Last post by  quadzjr
The term "falling effect" is something that you see thrown around a lot in relation to progressive springs. The idea being that due to the softer initial spring rate the car rolls a lot more in the early stages of a corner and then as the springs stiffen up the roll is slowed / stopped. The car "falls" into the corner.

Now, this isn't something that I have ever really noticed on my car, or perhaps I just never identified it properly (Eibach Prokits currently, previously Tien S-Techs). What I have noticed is a feeling of what I will call "roll instability". The car seems to roll too far, and then once it gets there never really feel solid or like it has much grip to spare. Not very confidence inspiring, especially at higher speeds.

That was last year. This year, with roll center adjusters at all 4 corners, that feeling is totally gone. The car has very little body roll, takes a set in a corner perfectly, and feels like it has tons of grip. Very confidence inspiring indeed, and much more fun to drive.

The other day I remembered something I had read a while back, posted by a member in one of my other threads. I will relink it here: Roll Center2007.pdf
The part that I was remembering I had quoted in my other thread, and will re quote here as well:

Wm. C. Mitchell said:
Stability results when the FAP-CG moment arm remains constant as the vehicle rolls. The chassis ?takes a set? rather than constantly seeking a new equilibrium. This can be expressed by minimizing the lateral movement of the KRC as the vehicle rolls. But this is an artifact: there are more direct ways to calculate this; namely with the change in FAP height resulting from ride. It should be one-to-one. (An easier way to visualize this is from the viewpoint of the chassis rather than the world. The FAP point should be constant as the wheels and tires move up and down.)
I am wondering, based both on that paragraph from the article and on my own experience, if the "falling effect" isn't caused by roll center movement more than, or at least as much as, by progressive springs.
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Didn't you make up some roll center migration graphs for the Mk II a while back? Can you link to those if you did?
These two threads have most of the analysis that I have posted on the MKII

I believe that my current data / analysis is a little cleaner that what is posted there (I have done several iterations of my analysis since then), but those should give the general idea.
the roll center adjusters do exactly just that. When lowering the car to the point the lower control arm starts pointing upward towards the wheel the Roll center starts doing some bad Juju. roll center adjusters bring the to links and lower control arms close to parallel to the ground again, which has optimal RC's.

On top of that the lowered suspension without the adjusters also have horrible toe out in bump and increased rate of positive camber gain.

so regaurdless of spring rate if the car is lowered to a point that causes multiple suspension issues as you are already aware.

Though my testing and analysis has been on a MK1. I have found much more confident feeling car when the control arms are close to level with the ground. When using Sport rate springs (Either the Eibach, or Jamex) and RCA's the car felt like you said much more "better" for lack of a better word. However before installing them I ran without and the car felt horrible.

However just like has been said on other books it is load/deflection/Force based. In testing as better and better tires were installed more deflections and loads were transfered, thusly things got worse. It wasn't as noticable on street tires, as the loads were not as high as s DOT'R tires provided which resulted in less RC movement.

However RCA's are not allowed in my class, so I went with the Carrol Smith route. Something along the lines of any suspension system will work as long as you don't let it.
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