@shadow118
The wrongly made suspension geometry probably doesn't help at all.
The strut doesn't have the steering axis going through the lower balljoint (MacPherson requires the virtual steering axis, not the strut tube) and the rear is completely wrong. It's not a strut; it's a semi-trailing arm. Take a look at my Singer, CTR-1, E30's to see how I did it. Singer is the best of those.
Although I really suggest to move the lower links farther away from each other on the Z on the trailing arms I make! There is a physics solver error if they get too close together and are too long (= too weak). Otherwise good.
Soon I'll update the E30, it will have a decent, similar rear geometry.
Also, I don't think the unsprung on the rear is quite so high; trailing arms are heavy but not *that* heavy. Maybe -10kg or so?
Also have serious doubts about the rear ARB; I REALLY don't think you'd be reaching 30k on any typical trailing arm ARB setup. E30 DTM with Delrin (Assumed 0.9x rate at wheel, but 1.0 is probably not far off either for any "solid" bushing and links) for example came out 3k to 9k for me.
Serious doubt about the power curve on the DTM car too. Smooth it out a bit at least.
I fixed the strut and put in my E30 rear into the DTM car, and it's better. Fix geo, smooth the power curve, calculate real rollbars and then you can probably run more realistic spring rates as well, not super front split like right now.
Making tires better would help, but okay, I can forgive that. I or someone else more knowledgeable would need to help with that.
I would help with the suspension but I need a break. However doing the above should produce a good result.