Physics Can a suspension guy sanity check my figures?

[McGherkin]

Hi, I've been trying to model my new coilovers in Assetto. I've got damper graphs for both front and rear (attached) and the spring rates are 7kg/mm front and 4kg/mm rear. I'm pretty sure the springs are right but getting the dampers right is proving an issue.

The wheel ratio for the front springs/dampers is .98 and the rear springs are .7, the rear dampers are separate to the springs and so their motion ratio is .9

I've tried working out the graphs below but the car comes out completely wrong, so I must be making a right mess of it somewhere. The dampers are adjustable and therefore I've tried to calculate the minimum and maximum rates for slow and fast bump and rebound.

If someone who knew what they were doing could take a look it'd be a massive help. Thanks in advance!

My workings:

Spoiler

SPRINGS:
7kg/mm FRONT 4kg/mm REAR (motion ratios .98 front .7rear)

DAMPERS:
motion ratios .98 front .9rear


************FRONT************

BUMP MINIMUM

0:0
0.01:98.1
0.30:1569.6

(98.1-0.0)/(0.01-0.0)
slow bump 9810 n/m/s x0.98axleratio 9613.8

(1569.6-98.1)/(0.30-0.01)
fast bump 5074 n/m/s x0.98axleratio 4972.5

BUMP MAXIMUM

0:0
0.05:1569.6
0.30:5297.4

(1569.6-0)/(0.05-0)
slow bump 31392 n/m/s x0.98axleratio 30764.2

(5297.4-1569.6)/(0.30-0.05) 3727.8/0.25
fast bump 14911 n/m/s x0.98axleratio 14612.8

REBOUND MINIMUM
0:0
0.01:147.15
0.30:441.45

(147.15-0)/0.01-0)
slow rebound 14715 n/m/s x0.98axleratio 14420.7

(441.45-147.15)/(0.30-0.01)
fast rebound 1014 n/m/s x0.98axleratio 994.53

REBOUND MAXIMUM
0:0
0.01:166.77
0.30:539.55

(166.77-0)/(0.01-0)
slow rebound 16677 n/m/s x0.98axleratio 16343.5

(539.55-166.77)/(0.30-0.01)
fast rebound 1285.4 n/m/s x0.98axleratio 1259.7

************REAR***********
BUMP MINIMUM

0:0
0.05:29.43
0.30:490.5

(29.43-0)/(0.05-0)
slow bump 588.6 n/m/s x0.9axleratio 529.7

(490.5-29.43)/(0.30-0.05)
fast bump 1844.3 n/m/s x0.9axleratio 1659.9

BUMP MAXIMUM
0:0
0.05:196.2
0.30:1962

(196.2-0)/(0.05-0)
slow bump 3924 n/m/s x0.9axleratio 3531.6

(1962-196.2)/(0.30-0.05)
fast bump 7063.2 n/m/s x0.9axleratio 6356.9

REBOUND MINIMUM
0:0
0.01:98.1
0.30:392.4

(98.1-0)/(0.01-0)
slow rebound 9810 n/m/s x0.9axleratio 8829

(392.4-98.1)/(0.30-0.01)
fast rebound 1014 n/m/s x0.9axleratio 913.3

REBOUND MAXIMUM
0:0
0.01:98.1
0.30:588.6

(98.1-0)/(0.01-0)
slow rebound 9810 n/m/s x0.9axleratio 8829

(588.6-98.1)/(0.30-0.01)
fast rebound 1691.4 n/m/s x0.9axleratio 1522.2


***************FINAL FIGURES******************
SLOW BUMP
FRONT min 9613.8 max 30764.2 clicks 705.013333
REAR min 529.7 max 3531.6 clicks 100.063333

FAST BUMP
FRONT min 4972.5 max 14612.8 clicks 321.343333
REAR min 1659.9 max 6356.9 clicks 156.566667

SLOW REBOUND
FRONT min 14420.7 max 16343.5 clicks 64.0933333
REAR min 8829 max 8829 clicks 0

FAST REBOUND
FRONT min 994.5 max 1259.7 clicks 8.84
REAR min 913.3 max 1522.2 clicks 20.2966667

 

[Kyuubeey]

Front bump max

0:0
0.01:245
0.30:637

(245-(0)) / (0.01-0.0)
24500 n/m/s = 23529.8

(637-(210)) / (0.30-0.08)
1940.90909091 n/m/s = 1864.04909091

Front rebound max

0:0
0.05:1392
0.30:5296

(1392-(0)) / (0.05-0.0)
27840 n/m/s = 26737.536

(5296-(1392)) / (0.30-0.05)
15616 n/m/s = 14997.6064

It's from MF1.pdf. Just check your values and syntax, and convert kg to n correctly.


Rear is uber soft, would need to zoom in with an image viewer to get the points, can't be bothered.

The fronts come out stiff on slow but they have like 1cm/s knee on bump so it's actually quite soft. It'll be stiff initially but the movement from roll is enough to go into fast rates I think.

Rebound is uber stiff as per usual of tuner dampers, for jacking into the bumpstop. Probably feel like ****.

For rear rebound, I'd suggest a 4cm/s knee, bump is okay at 1cm/s. You're going to have to pick one knee for every step, so for front rebound I biased towards the stiffest setting, with a bit more error at lower settings. Lower force = less of a problem IMO.

 

[McGherkin]

Something seems really wrong with those figures though. For example I set all the sliders to give between 100 and 10000 n/m/s as a test and the car seems to drive best around the 5000 mark up front and 4000 mark at the rear, with 7000 and 6000 feeling what I would equate to max stiff on the real thing. Obviously setting 23000 comes in massively overdamped and whilst that would be the highest the dampers could go, I'm sure that must be way too stiff.

How are you getting your numbers for N out of the graph? I was converting from kgf to N by x9.81 but I can't see any correlation between that and the 245 and 637 you got.

 

[Kyuubeey]

Those probably aren't the exact dampers on your car. The same damper model has several different valvings for different cars, usually. To me it looks like you've mixed up two completely different cars' kits. The one I made might be fine for a DWB rear with 0.60 MR for example.

I used my eyes to just sight the value, then threw it into a converter, which basically just does x9.81 as well. Make sure you're looking at the same graph and actually in the same spot.

 

[McGherkin]

Very possible I'm guessing. The car does use MFR dampers up front and 44R-03 dampers at the rear.

I'm guessing I'll just have to wing it and make what 'feels' right, but it would have been nice to plug actual figures from the dampers into the sim.