Roll Center movement

[razz]

Hello,
I am struggling to gain some understanding on roll centers , I have plotted out the roll center on a double wishbone front suspension set up .
the roll center plots to about 5'' above ground - as the chassis rolls in increments up to3 deg the roll center moves considerable (18'')to inside un weighted wheel although it's ht remains faily steady, my concern is how much is generally consider acceptable.looking through books lots of refs are made to RC hts but its difficult to find info on the parameters to aim for on sideways movemove of RC - or did I turn 2 pages together ?

[AU N EGL]

Originally Posted by razz

Hello,
, my concern is how much is generally consider acceptable.

As little as possible, Dead flat ( no body roll ) cornering would be the ideal.

[Goran Malmberg]

Rc is a very complex situation to discusse. It involves cambercompensation curves that has to be taken in to concideration and thereby the downforce for the car. However, it is no bigger problem to design a A-arm setup that keeps the Rc pretty much the same location during roll, so I dont see any reason not to do so. But, as the car roll, weight transfer is taking place, making the outer wheels taking a bigger load. To keep the jacking forces the same the Rc should move to the inside wheel accordingly to weight transfer in %. This means that if the outer wheels is carrying 75% of the load, the Rc should be at 75% from the loaded wheel away to the inside wheel.

In this particular discussion Rc is refferred to the same spot as where the forceline intercept.
Now, Forceline interception is not really the spot the car acually roll about.
How the car roll is another question not discussed here. One very important thing is to keep the Rc height fixed during roll (read forceline interception) the same as this govern the real Rc location.

Regards
Goran Malmberg

[razz]

thanks Goran for that imput -
Ive been messing with this on a very simple softwear suspension package - and made mods to the inner pick up points and upper w/b lengths that gives me a RC 3 1/2 " above ground and at 3 deg roll moves 7 1/2" towards the unwieghted wheel , with 1.5 deg camber change. this I feel is about the best I can do taking in the practical implications - hope I'm moving towards the right goals without causing other problems I'm not awear of

[Goran Malmberg]

Originally Posted by razz

thanks Goran for that imput -
Ive been messing with this on a very simple softwear suspension package - and made mods to the inner pick up points and upper w/b lengths that gives me a RC 3 1/2 " above ground and at 3 deg roll moves 7 1/2" towards the unwieghted wheel , with 1.5 deg camber change. this I feel is about the best I can do taking in the practical implications - hope I'm moving towards the right goals without causing other problems I'm not awear of

If the interception of the forcelines is moving to the inside wheel while keeping its height the same level you will be comming out fine. You dont nessesarly need to keep it absolutley the same % as the weight transfer, and you probabley dont even know for sure what Wt looks like so its a guess anyway.
If you should make a margin in any direction I recomend beeing in the direction to the centre of the car rather than closer to the inside wheel.

What is the Ic distance?
Goran Malmberg