Behavior of an unusual A arm layout

[englertracing]

Hello! Im new here.

warning i am not sure you will be able to compute my sophisticated schematic, LOLOL JK
sry it looks like a 2 year old drew it with a crayon, I don't have cad anymore so paint will have to do..... I hope its legible

Im not even planning on using something like this or claiming its some revolutionary invention. I actually joined this site some time ago to post this but never got around to it, now i'm at work on grave yard shift and its bugging me again so i decided to come here and post

a friend and I talked about something like this for an off road car just B.S.ing one eccentric friend to another (neither of us are building off road cars in the foreseeable future)
Infact i think there is something wrong with it thats why i have never seen or heard of it being used?
have you?
Im sure many people have thought about it.

I first mentioned offroad application but i want to discuss it in a ROAD car application.

It seems like a front suspension of this design would have opposite reactions to jacking / anti jacking vs a SLA setup. because the jacking or anti jacking would be acting on the other side of the car
(aaahhhh damm im getting all confused just thinking about this thing)

what would it do with an above ground roll center? (you elaborate here)
well turning left it would increase body roll with the left side of the car trying being thrust up by the right front tire.
while the left front is being drug along and trying to lift off the ground and pull the left front of the car down (well not so much pull it down)

how about a below ground roll center?(you elaborate here)
the right front would try to pull down the left front in a left turn (or mostly the right front wheel will have an upward unloading movement)
and the left front wheel would have a jacking effect lifting the right front of the car

what about an on ground roll center? (here too)

with an on ground roll center could this suspension have a stable roll center location? (and here)

would you say this would behave the same as a a Ford twin beam?

hopefully some of that was coherent its 5am on a graveyard shift HAHA

[Z]

Englertracing,

Assuming that the bend in your lower wishbones simply indicates that they cross over structurally, with no kinematic interference, then the above setup will behave exactly like any other wishbone setup, all other things being equal.

So, if "high RC" (= steep up-to-car-centre lateral n-lines), then less body roll, but more upward jacking.

If "below ground RC" (= n-lines slope down-to-car-centre), then lots of body roll, and downward jacking.

If "RC on the ground" (= horizontal n-lines), then medium body roll, no jacking, RCs shoot off to lateral infinity with slightest body roll, but stable and well-behaved handling (contrary to what many experts will tell you!)

And so on...

Z

[englertracing]

Englertracing,

Assuming that the bend in your lower wishbones simply indicates that they cross over structurally, with no kinematic interference, then the above setup will behave exactly like any other wishbone setup, all other things being equal.

So, if "high RC" (= steep up-to-car-centre lateral n-lines), then less body roll, but more upward jacking.

If "below ground RC" (= n-lines slope down-to-car-centre), then lots of body roll, and downward jacking.

If "RC on the ground" (= horizontal n-lines), then medium body roll, no jacking, RCs shoot off to lateral infinity with slightest body roll, but stable and well-behaved handling (contrary to what many experts will tell you!)

And so on...

Z

Hi z

The kink is just to allow the ARM to clear the frame.

Are you sure the high roll center would not actually induce more body roll because the lower controll ARM is mounted to the opposite side and will actually jack the inside?

[Z]

Englertracing,

You are making the same mistake that too many other people make here (including waaayyy too many "experts"!!!).

In this simplified 2-D explanation, the Lower Control Arm ("LCA") can only transmit forces that are directed along the line passing through the two BJs at its ends. That is, any LCA force's Line-of-Action must be coincident with the LCA's n-line (= line passing through the BJs). This is a most fundamental principle.

Now, that LCA force (let's call it F.lca) can be decomposed into any amount of other force "components" by repeated use of the "Parallelogram of Forces" Rule of Statics. Let's assume that F.lca is decomposed into only two components, say, a horizontal component F.lca-h, and a vertical component F.lca-v. This vertical component might be called the LCA's "jacking" force (as you have called it).

The BIG MISTAKE (as before, committed by too many "experts") is to move this jacking force component F.lca-v around WILLY-NILLY, WITHOUT ALSO TAKING WITH IT THE OTHER COMPONENTS OF THE ORIGINAL FORCE (in this case F.lca-h).

So, if you have a short LCA, and you are thinking about the jacking force acting on its chassis mounting point, and you then mentally lengthen the LCA so that the chassis mounting point is now on the other side of the chassis, and you now think about the jacking force acting there, then YOU ALSO HAVE TO MOVE THE HORIZONTAL F.lca-h FORCE TO THIS NEW (HIGHER) MOUNTING POINT, as well!!!!!

Apologies for the shouting, but I find that it helps with the communication. :)

Anyway, when you also account for the horizontal F.lca-h force's effect at its new, HIGHER, position, you should see that there is no difference between long or short control arms (at the instant) whenever they have the same angle wrt ground (or more accurately, they have the same n-lines).

All this is easier described with pictures and working through numerous examples, but I hope you can follow the above...

Z