Dampers bump - rebound

[Ciro Pabón]

... Can somebody put this into a physical formel to calculate the amount the spring is compressed.
I tried this once but failed immediately.

I can give you the simplified form civil engineers use to calculate the IRI (International Roughness Index) wich measures how many millimeters you move up and down while you move one millimeter along a road: it's the old and well known "Quarter Car Model". I don't have at hand the equations (I made once a program to solve the integral you have to make, but I was young and did not have children asking me to play outside, like today ). Perhaps someone can give you his own program or you can google for it. There is also a "Half Car Model" we discussed at some thread here, more complicated, which is more accurate if you want to reproduce the pitch sensitivity of the aerodynamic components of the car.

This is the model:



The car chassis is the "sprung mass" ms.

The wheel assembly is the "unsprung mass" mus.

The spring is ks and the damper is bs, placed between the car body and the wheel assembly

The spring kt is the tyre.

The variables xs, xus, and r are the car body travel, the wheel travel, and the road disturbance or bump.

The force fs, kN, applied between the sprung and unsprung masses, is controlled by feedback and represents the active component of the suspension system. If your car has not active suspension, omit it.

In that condition (no active suspension) if you define x1:=Xs', x2 = d(Xs), x3:=Xus and x4:=d(Xus), were d() means the derivative, then this are the equations that describe the behaviour of the quarter car dynamics (the dot on top of variables means the derivative):



Typical values for IRI calculation are:

ms = 290 kg
mus = 59 kg
bs = 1000 N/m/s
ks = 16182 N/m
kt = 190000 N/m

Hope this helps. If I have time (sorry, I have to play football with my 8 years old kid AND he is tugging my arm while I write this! ) I'll check my old class notes to look for the solution to the equations.

What you're looking for is the difference between X1 and X3 (or Xs and Xus) wich shall give you the spring compression, BTW. The solution I have somewhere buried gives you only X1, that is, how much the chassis moves up and down.

You have to integrate to solve the differential equations. I'm sure someone has to have the equation solved. Perhaps Reca? Or you can use Mathematica, if you have it.

[mep]

thank you ciro
it's not so importand better play with your son.
The damper think is more interresting.

[David Anthony]

mep if u ever step over to rfactor, and wanna race in a leauge pm me. I race for http://www.venezuelaf1.net/ its a international race leauge. We do all kinds of this tuning stuff, dampers etc etc. everything counts to win a race here. LOL

With damper i usualy have them always soft with the rebound a little stiffer. The fast dampers are generaly used for realy fast movements, like riding curbs, for exmaple monza, the first turn, u stiffen the fast dampers as it helps stable the car when you go over the curbs.

It also makes the car driver smoother at high speeds, if u are getting bouncing at high speed play around witht them, and the 3rd spring.

[mep]

Last time an ingeneer told me that the rebound is slower
because of the springs bouncing back and so the tyres losing ground
contact.
This would make sence for the third spring making rebound stiffer
than bump.

But what about the two outer springs they are in some case
conected with roll so would it make sence to make rebound faster
then bump so that the chasis comes fast back to normal position
after driving through a corner?

[modbaraban]

So adding packers is useless and brings only disadvantages?

This may clarify it

[mep]

Thanks for the link but I have a problem with getting the car low to the ground.
Packers do the oposit.
I have the theory that the car has always to be lower at front than
at rear.
But I didn't get the front lower. And at rear I have suspension as soft
as possible for ideal corner behavior.

[modbaraban]

I have the theory that the car has always to be lower at front than at rear.

Sure! In my setups the rear is almost twice as high as the front!

[mike]

i am playin the game in the Rh2005 mod and i cant understand why my cars alway spin when i hit a chicane while i never have the problem using the 2004 car
how can i fix this problem ?
i have try turn the anti roll bars harder, and i did made it less spining tending

[modbaraban]

spin when i hit a chicane

You mean the curbs?
I'd set the rear anti-roll bar softer, softer rear and front fast rebound, harder front anti-roll bar.

Also have a look at your camber settings. Extreme negative camber on the front may cause oversteer and increased tyre wear. Exreme negative camber on the rear may cause bad traction out of corners and brake locking too early... and again increased tyre wear.

[mep]

Sure! In my setups the rear is almost twice as high as the front!

So then tell me how you do it.
I mean I know how, but I want to reach this by mostly lowering the front
to the limit. But this doesn't work so good because there is one point where you didn't get it lower. Especially because another theory is to
have the springs at front harder than at rear.
At rear I have the 2 outer springs as soft as possible.




This is importand for you mike.

i cant understand why my cars alway spin when i hit a chicane

I also play 2005rhmod and have had a bit a traction problem out of low
corners like Nürburg first one and France hairpin.


Make rear springs soft and increase at the tyre section the Vorspur
(dont know how to say it in english track or so you will find it if not ask again)

Set it to positive like maybe +0.30 or so, staybles the rear a lot.

[mep]

Maybe we can get some real setup discusions here and
can maybe hit once to test it online.

Fell free to post stup depending things

[modbaraban]

So then tell me how you do it.

I'll post a screenshot of those SUSPENSION related pages later.

PS: and yes, the front is as low as possible (or close to it).