Roll center question

[ivan182]

Hy, I have a problem understandig something about roll center.
If roll center is at the same point as CoG then there is no roll moment and I red in some books that then is no chassis roll.(roll gradient =0)
But even if there is no roll moment , load transfer still occurs and the outer wheel goes in bump , inner in rebound position and the chassis has to roll (tilt) cause of this. This means that the chassis will roll no metter where roll center is ,right?
So in theory I might need to install anti roll bar even if roll moment of my car is zero. Does this have sense or I am getting something wrong?

[ivan182]

Hy, I have a problem understandig something about roll center.
If roll center is at the same point as CoG then there is no roll moment and I red in some books that then is no chassis roll.(roll gradient =0)
But even if there is no roll moment , load transfer still occurs and the outer wheel goes in bump , inner in rebound position and the chassis has to roll (tilt) cause of this. This means that the chassis will roll no metter where roll center is ,right?
So in theory I might need to install anti roll bar even if roll moment of my car is zero. Does this have sense or I am getting something wrong?

[Goost]

if the roll axis was Always at the CG then the only roll would be from the tyres acting as springs - even if there was no suspension at all load transfer would occur. The trick though is that, assuming you have an SLA suspension like most of us do, the roll centers don't really sit still, as soon as there is bump or droop then they start to shift...

[ivan182]

that is the thing that I do not understand. If the roll axis is always at CG shouldn't the springs still go into bump on laden wheel and rebound on unladen couse of weight transfer?
causing roll together with tyres acting as springs
and if not please explain why...

[Mike Cook]

Draw a free body diagram...dude.

And then make a spread sheet that calculates weight transfer. You will figure it all out with a little thought and milliken.

[ivan182]

dude..http://fsae.com/groupee_common/emoticons/icon_smile.gif
if it is that siple to describe why dont you just explain me in a few words ?
if you understand it of course...

[sidkash14]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ivan182:
dude..http://fsae.com/groupee_common/emoticons/icon_smile.gif
if it is that siple to describe why dont you just explain me in a few words ?
if you understand it of course... </div></BLOCKQUOTE>

Ivan, the point that Mike is trying to make, is for you to draw the FBD and to figure it out yourself. No point if he just 'tells' you how it works.

Good Luck!! http://fsae.com/groupee_common/emoticons/icon_smile.gif

[ivan182]

ok. I did meke a drawing and figure something out. I never guessed that this is same thing like antis in longitudinal plaine,where forces are reacted completley through A-arms when the line connecting contact patch and instant center passes through CG.

[Drew Price]

You got it!

It's exactly like anti's, but usually people understand the front view roll center concept and do NOT understand side view anti's for some reason.

[Shebert]

The ''anti'' comparision is good. Look at the anti-dive formula, you will see that the brake bias is part of the equation... Ask yourself the following question: Does my inside tire do the same job as my outside tire? Do your free body diagram, you will understand why your car still roll (not just from the tires), you will also understand jacking.

Cheers,

[ivan182]

Thank you for your answers! I have some problem understanding other things that i came across...

1.question about load transfer (lateral)...
In 'Tune to Win' it is written that higher roll stiffness wich arises from springs does not influence the overall lateral load transfer,but higher roll stiffness that arises from antiroll bar does affect overall load transfer....
At the same time in Milliken equation for lateral load transfer does not take in account where the roll stiffness of pair of wheel come from...
so what is right?

2.question is about roll moment....
I dont understand how higher roll moment on one end of car results in faster lateral load transfer and if roll moment is higher at front than at rear , the car will have tendency to udersteer.....(Tune to win, Fundamentals of Vehicle Dynamics)
I understood that lateral load transfer arises from : instantaneous transfer through suspension arms and from compression of springs wich couses roll moment (this lasts for a certain period of time).....
So doesnt that mean that if roll center is lower on front than at rear in dependence of CG (higher roll moment), less transfer will be accomplished instantaneous through suspension arms and more will come from compression of springs. On the other hand in rear instantaneous load trasfer trought suspension arms will be higher and rest of transfer from roll moment will be accomplished at lower roll angle than at front and the car should have tendency to oversteer . Does this have any sence?
For example above static weight transfer is 50%-50% and roll rates are same front and rear.