Physics How do I make proper Coilovers?

T0rqu3_ · Jul 22, 2020

I'm working on a car which I'm doing from the ground up. It's a pretty extreme one. Almost 1:1 power-weight-ratio (774hp/1000Nm), lightweight in general (900kg) , almost GT3 level aero and top speed sits ~340km/h. They weight distribution is 37/63 and is matched by the aero +/- 5%. Everything is working fine but the coils are giving me a hard time. The static height is at about 80mm but at 300km/h I'm basically hitting the bump stop from the down force weight alone. Even if I set the spring rates to 250000 it doesn't make a difference and no matter in which range of bump and rebound values I'm working, road bumps make it lose grip way more than they should.
It just feels very unorganic and rough

This is driving me crazy

Pls help

Stereo · Jul 22, 2020

I don't think there's any shortcut to that, you'll just have to learn how to set up a car

Ghoults · Jul 24, 2020

Check your ground collider height and rear bumpsteer at first. Also check you are setting your bumpstop parameters correctly. Easy to get them wrong and have different amount of wheel travel than you think. Also remember that all susp.ini values for example are "squeezed" by setup.ini values. If the susp.ini values don't fit inside the setup.ini parameter ranges the setup.ini is the one that matters.

Kyuubeey · Jul 24, 2020

BUMPSTOP_UP and DN are measured from the suspension's design height. You can find it with the "Telemetry" app section "suspension travel" by letting the car settle on the springs. I suggest 1l fuel and tap the gas a bit to make it start settling, then wait and round it up to 1mm. Result is in mm.

Put that into rod_length and you find your 0 position where everything is referenced from.

PACKER_RANGE is the current suspension travel + current travel to packer, AT THE WHEEL. Convert damper to wheel with (Distance / motion ratio).

EXAMPLE:

ROD_LENGTH=0.146 ;0.156, 0.146
;-10mm driver mass

;Spring MR = 0.690^2, 0.6695040537^2
;Damper MR = 0.690^2, 0.6695040537^2
;Shock angle 14.0deg = x 0.97029573

BUMPSTOP_UP=0.10455500547
BUMPSTOP_DN=0.07468214676
PACKER_RANGE=0.1758728587

;suspension travel = 0.156 + 0.0198728587
;bump stop travel = 0.020 - 0.010,
;0.0298728587 - 0.010 = 0.0198728587
;chassis stop travel = 0.070, 0.10455500547
;rebound stop travel = 0.050, 0.07468214676
;bumpstop length = 0.050 (Stock 0.050)

T0rqu3_ · Jul 26, 2020

Thanks! Where can i find the collider height? Is it literally the coordinates of the collidermodel?

T0rqu3_ · Jul 26, 2020

Kyuubeey said:
BUMPSTOP_UP and DN are measured from the suspension's design height. You can find it with the "Telemetry" app section "suspension travel" by letting the car settle on the springs. I suggest 1l fuel and tap the gas a bit to make it start settling, then wait and round it up to 1mm. Result is in mm.

Put that into rod_length and you find your 0 position where everything is referenced from.

PACKER_RANGE is the current suspension travel + current travel to packer, AT THE WHEEL. Convert damper to wheel with (Distance / motion ratio).

EXAMPLE:

ROD_LENGTH=0.146 ;0.156, 0.146
;-10mm driver mass

;Spring MR = 0.690^2, 0.6695040537^2
;Damper MR = 0.690^2, 0.6695040537^2
;Shock angle 14.0deg = x 0.97029573

BUMPSTOP_UP=0.10455500547
BUMPSTOP_DN=0.07468214676
PACKER_RANGE=0.1758728587

;suspension travel = 0.156 + 0.0198728587
;bump stop travel = 0.020 - 0.010,
;0.0298728587 - 0.010 = 0.0198728587
;chassis stop travel = 0.070, 0.10455500547
;rebound stop travel = 0.050, 0.07468214676
;bumpstop length = 0.050 (Stock 0.050)

Determining the 0 position is a really good tipp! I'll do that now ..but this is seriously complicated stuff. What role does my basey value play in all of this?

Kyuubeey · Jul 26, 2020

Collider.ini. It's referenced from CoG height. Use Content Manager's CM showroom to view both of them easily. You can have multiple ground colliders, too.

Basey is essentially just to determine CoGH. I suppose if it becomes very low or high, weird things start to happen.

T0rqu3_ · Jul 26, 2020

Kyuubeey said:
Collider.ini. It's referenced from CoG height. Use Content Manager's CM showroom to view both of them easily. You can have multiple ground colliders, too.

Basey is essentially just to determine CoGH. I suppose if it becomes very low or high, weird things start to happen.

Ok I checked my colliders they are all set. On this particular car I want my Y-axis distance fron CoG to mid of wheels to be zero. they are on one line. So does my basey value need to be set to 0?

Kyuubeey · Jul 26, 2020

T0rqu3_ said:
Ok I checked my colliders they are all set. On this particular car I want my Y-axis distance fron CoG to mid of wheels to be zero. they are on one line? So does my basey value need to be set to 0?

Yeah, I think so. It's ref from center of wheel so it'll take tire diameter into account IIRC.

Is the CoG really IRL at that spot, or just for testing?

T0rqu3_ · Jul 26, 2020

Kyuubeey said:
Yeah, I think so. It's ref from center of wheel so it'll take tire diameter into account IIRC.

Is the CoG really IRL at that spot, or just for testing?

Yes it actually is. I might even be lower than the middle of the wheels. But for now I'll assume they are the same height.
So I have my basey at 0 now and the telemetry shows me values: front: 60mm and rear 29mm which I set the rod length to. The car sits at the exact height I want it at which is 80mm. So what UP DN and RANGE values do I need now?

Kyuubeey · Jul 26, 2020

Hm, weird.

Bear in mind that (As I've been told, at least) "front" and "rear" CoG don't exist, there's just a centralized point, so you'll want to also lower your front there if your CoG really is so low. The reason they can be separated is basically just to tell how much rake the car has "built-in".

UP is wheel travel to your point of choosing from the center. I either use rubber chassis stops, or the end of the shaft.
DN is wheel travel to your droopstop from the center.

PACKER_RANGE is that axle's suspension travel + the wheel travel to the packer from the height that you've currently set up the car at.

For example 0.060 + 0.030 = 0.090.

Mind you WHEEL travel, so if you have damper values, convert them to wheel with "/ motion ratio".

T0rqu3_ · Jul 26, 2020

Kyuubeey said:
Hm, weird.

Bear in mind that (As I've been told, at least) "front" and "rear" CoG don't exist, there's just a centralized point, so you'll want to also lower your front there if your CoG really is so low. The reason they can be separated is basically just to tell how much rake the car has "built-in".

UP is wheel travel to your point of choosing from the center. I either use rubber chassis stops, or the end of the shaft.
DN is wheel travel to your droopstop from the center.

PACKER_RANGE is that axle's suspension travel + the wheel travel to the packer from the height that you've currently set up the car at.

For example 0.060 + 0.030 = 0.090.

Mind you WHEEL travel, so if you have damper values, convert them to wheel with "/ motion ratio".

Thanks man! So I have both my basey values set to 0 and my UP at 60 DN at 50 and my Range at 110 .. which seems realistic to me.

So in my understanding: The coil can compress 60mm before hitting the upper bumpstop and decompress 50mm if the car is lifted up by 50? Is that realistic for a GT3 .. LMP .. F1 car? Or what would you recommend from experience? The real car has a KW Competition coilover set and I want if suitable for the Nordschleife mainly.

Kyuubeey · Jul 26, 2020

That kind of range's not too far off. I would suggest you try to find damper stroke ranges, KW just might list them somewhere.

If your MR is under 1, you'll want to convert to wheel values.

T0rqu3_ · Jul 26, 2020

Kyuubeey said:
That kind of range's not too far off. I would suggest you try to find damper stroke ranges, KW just might list them somewhere.

If your MR is under 1, you'll want to convert to wheel values.

OK the car is driving a lot better already!
They have graphs on their website but I dont understand how to translate those values into the game

. https://www.kwsuspensions.net/media/downloads/KW_Katalog_Motorsport_2017_en_web.pdf
Under 3a and 4a are the graphs.. maybe you can tell me what I have to set my bump rebound and thresholds to .. since I have noooo idea

What are those mass and wheel ratios?

Kyuubeey · Jul 26, 2020

I can't be arsed to teach you everything for free right now, but I'll dump you the syntax and you can figure it out.

Newton force on left, meters velocity on right. Newton/meter result. Lowest distance is your knee.

Front bump

0:0
0.08:210
0.30:441

(210-(0)) / (0.08-0.0)
2625 n/m/s = 2323.17577417

(441-(210)) / (0.30-0.08)
1050 n/m/s = 929.270309669

Front rebound

0:0
0.10:430
0.30:1255

(430-(0)) / (0.10-0.0)
4300 n/m/s = 3805.58317293

(1255-(430)) / (0.30-0.10)
4125 n/m/s = 3650.70478798

Anything else you can search online with the term and you'll find an explanation.

T0rqu3_ · Jul 26, 2020

Kyuubeey said:
I can't be arsed to teach you everything for free right now, but I'll dump you the syntax and you can figure it out.

Newton force on left, meters velocity on right. Newton/meter result. Lowest distance is your knee.

Front bump

0:0
0.08:210
0.30:441

(210-(0)) / (0.08-0.0)
2625 n/m/s = 2323.17577417

(441-(210)) / (0.30-0.08)
1050 n/m/s = 929.270309669

Front rebound

0:0
0.10:430
0.30:1255

(430-(0)) / (0.10-0.0)
4300 n/m/s = 3805.58317293

(1255-(430)) / (0.30-0.10)
4125 n/m/s = 3650.70478798

Anything else you can search online with the term and you'll find an explanation.