Car setup guide from communities

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ACC Forum

Aristotelis' post
As you have probably understood by now, the cars are very pitch sensitive. When you brake and turn in, the aero balance moves way too much to the front (if you let the car pitch) and makes the car oversteery and unpredictable, making you lose time trying to control it or downright spin. The higher the speed, the worse it gets.
To control this behaviour you need a car that pitch less (the nose goes down less) during braking, so that the aero "platform" as they call it, remains stable. To do this you need to use stiffer suspension and mainly a stiffer front end. Enter the scene, bumpstops. Teams practically "ride on the bumpstops" as they call it. The more the car is pitch sensitive or the suspension geometry permits it to pitch, the more bumpstops you need. Both stiffer and riding on them sooner. So you do the following if starting from scratch.
Start with the front bumpstops. Make the rears with as big bumpstop range as possible. (preset setups are like this already)
You start with the softer possible bumpstops (lower bumpstop rate numbers) at the front. Remember they are not liner but they raise their stiffness the more you compress them, so they remain predictable.
You close (lower) the front bumpstop range gap. Often teams call this bumpstop "window" meaning the space that the suspension can compress before it touches and "rides" the bumpstop. usually it is very narrow and many times can be practically 0, so that the suspension rides on the bumpstop almost always.
If you have completely close the font bumpstop range and the car still unsettles at braking turn in, you start raising the front bumpstop rate until the car is stable in braking turn in.
Now comes the interesting part. Once you have the car stable in braking turn in, you'll notice that you might have power understeer. Because the front end become too stiff, it pushes a bit too much while trying to accelerate out of the turns, usually at high speed turns. Try the following:
Raise a bit the front bumpstop range (bumpstop window as we said) to let the suspension a bit more free to roll and softer when in extension (on power). If you do, always check the braking turn in stability
Lower a bit the bumpstop rate. One click should do
Play with the front antiroll bar (ARB). This is tricky as you might achieve less understeer if you soften it (lower numbers) as you might expect. But attention, if this doesn't work, go the other way around and you might get a bit less understeer if you stiffen it (!) because by doing that you might make the suspension go less on the bumpstop and make the rear roll more and rotate the car.
The following part is important to understand how modern cars "work".
Consider that you have a wide range of values in your setup. A range like the following
soft|--------------------------------------------------------|hard
Now in all the usual textbook and older sims, the rule of thumb was always, "softer setup=more grip, less precision. Harder setup=less grip, more precision".
Well this is not exactly the case in reality, especially with modern cars and advanced aerodynamics.
Here's what is happening now
soft|--------()------------()------|hard
What do the (__) mean? This is the so called "window of operation" that a modern car can have. This short range that changes from car to car and track to track and ambient conditions and driver preferences, is where the car performs better and generally "works" and reacts correctly to setup changes. Outside that ranges, unpredictable things can happen and generally the car "doesn't work". Obviously the above is just an example. You might get 1 only range, 2, 3... or whatever. More or less wide ranges and so on. So to give a simple typical example; the rear of the huracan has some strange camber gain suspension geometry and loses a bit of camber. So you soften the rear arb to gain traction and it works, soften it again and it works again. Do some other changes, soften some more and all of a sudden the rear is floating. It oversteers at entry, it is less predictable at power exit, it's bad. You lower more the value (soften) of the rear ARB and it's even more.
You're out of the operation window of the car. You go back stiffening it and you regain grip!
Yes I know it sounds completely the opposite of what you think, the unexperienced might believe the "software is broken", but it's not. You're gaining real world experiene. Modern cars have operating windows and you need to find them and stay in there. The moment you go out and something bad is happening, turn around your values and go back again. That is why in ACC is even more important than ever, to do just 1 or 2 clicks at a time and try. Do 4 click changes and goodbye you're lost.

P.S. Yes you can add bumpstops at the rear too, and advanced teams do it. But it's dangerous and definitely unpredictable on bumpy circuits and on the kerbs. Sometimes you can't avoid it, like at Spa, that some cars need rear bumpstops to keep the rear end from scraping at Eau Rouge, but again as soft as possible and as wide range gap as possible. Generally adding rear bumpstops should be your last resort and you should be very careful with them, or even modify the way you drive around the track and kerbs, to make sure you don't get nasty situations from the rear.