Car set-up wisdoms

I'm going to start it like this.... these sort of thing deserves to be shared.

I stumbled on this lut table this guy made into a pdf about the tire grip/wear/pressure, will post it as soon as I find it or link it.


"Did you know you can get more grip from road car by lowering the tyre pressures and adding camber? I advice you to start from 25 to 28 psi for street tyres depending on the weight of the car, and 22 to 26 for semislicks. If you overheat, add a bit of pressure, but not much, besides street and semis will always overheat under the big weights of road cars.

Then add as much negative camber at front, and stay around -2 at the rear for high powered RWD cars and a bit more than that for low powered road cars. Mainly, if it oversteers on lift off a lot, add rear negative camber

Aliens of course do not need this kind of advice so don't attack me "


-Aristotelis-



"Can I ask how much slower than the WR you are?
Because if you are anything over 1.5 seconds learning the optimum tyre pressures/temps and using dev apps, will not help you. Focus on lines and general car balance, than details. Turn off all the apps, and just drive"


-Aristotelis-

 

Before talking about setup, I'd like to say a few things:

Drive enough to be able to spot the smallest setup change, or your testing will be useless, and only change one thing at the same time in small amounts for the same reason. Once you get good, you can generally just make a setup fast that will work for you, but it still takes tweaking to make the car really do what you want.

I'll start with some general "everyone should know" things.

General:

There is no such thing as a magical alien setup that will shave a second or two off your times by abusing the physics engine, there are just alien drivers who make absurd setups work. I know because every time I share a setup with a few of my fast friends, they say it's terrible, and I say theirs is terrible.

Enable dev apps in [assettocorsa/system/cfg/assetto_corsa.ini]. This unlocks a host of apps that show alignment, temps, pressures, aero, damping ratio, wheel rate, etc. in realtime.

It's nearly always better to run a high car with softer springs than to run a lower car with stiffer springs, because the needed level of dampers and roll bar makes the car very skittish, if you're driving such a stiff setup on the wrong track with the wrong style.

Don't lower your racecar too much: your CoG may become lower but your roll center and instant center will also suffer, and your camber/toe curves will go all whack. On some cars like touring cars, this isn't so much a problem, while in GT cars you must run proper geometry, because you'll just bottom out with a low car, anyway. Lowering a car also means that the above can happen, when you go too stiff.

Instead of increasing downforce and drag via wings, increase rake, or the height difference between the front and rear suspension. Aero isn't simulated so well that rake actually provides more downforce in the rear due to better airflow over the front wing due to a better angle, but it does allow you to get a better turn in at low speed, and more downforce at high speed without causing "useless" drag and downforce.

When tweaking the differential, start with 0 preload and 80% power/20% coast. Then work your way up closer to 50% in power and coast, and add preload once those are done. If you oversteer too much on the brakes or the throttle, increase coast or decrease power. Increase preload if it kicks in too suddenly.

Dampers for the driver:

Dampers resist movement by converting kinetic energy into thermal energy. If a stiffer spring means a faster wheel, a stiffer damper means a slower spring. Dampers are a compromise, and they are used to control wheel oscillations, provide faster or slower loading or unloading of the suspension and to balance car handling and tire temperatures. Dampers in AC are measured in N sec/m, although in setup you will only ever see the clicks and damping ratio.

Dampers do not mean the ultimate achievable amount of roll/dive/squat/lift! They just mean how fast it happens, so in a corner, they dictate what kind of balance you have.

Slow damping means the resisting of movement in a direction at under 1m/s shaft speed or so. Or in other words, braking, turning, accelerating etc.

Bump means, for example, the car lowering onto the suspension in braking or acceleration, or right after you hit a big jump in a rally track. If you go too low, you hit the bumpstops, hence "bump".

More bump in the front means that the front resists diving, which gives you more stability in braking, higher response speed and set speed (Taking a set means that the car is balanced and has done all it's weight transfer) and higher tire temperatures.
If your car is unstable on brakes or doesn't respond fast (It feels like it's "lagging" on the front suspension) then you might want to increase front bump.

More bump in the rear means that the rear resists squatting, which means that your car gets more power-oversteer, faster transition into turning after braking (Faster "rotation) and faster set speed.
If your car understeers on the throttle and/or understeers coming off the brakes, you probably need more rear bump.

Rebound means the suspension "rebounding" from a bump, or the suspension raising. When you accelerate, your front rebounds, and when you brake, your rear rebounds. If you have insufficient rebound damping, your car can be very nervous and unstable.

Rebound is generally the reverse of the bump effect: more rebound in the front means more oversteer on the throttle, more rebound in the rear means stability on the brakes.

The reason this is, is because when you accelerate, the front wants to raise slower, thus producing a more front biased weight distribution and while you brake, the rear wants to raise slower, which means a more stable brake application because your rear doesn't just jump up, suddenly leaving a lot of weight on your front.

I use rebound to control weight transfer and make handling smooth, and to preserve my underpants.

Dampers effect the car side to side, so higher bump on your right side means that your car will want to roll slower when you turn left, meaning that the weight doesn't flop around as much and the car takes a set faster.
Of course, more rebound on the right side also means that once you start unwinding the steering, your car doesn't get unweighted so fast, and takes longer to take a set, but also allows less weight to flop around.

A more slow damped car is a stabler ride, that slides and turns easier, with less car sickness to the occupants. That's why aftermarket dampers generally feel better than very old, stock dampers. An overdamped car on the other hand will just slide around, and while it might feel very responsive (I'm looking at you, Honda, overdamping all your Type R's...) it will have a lower potential and be more nervous than a properly damped car.

Fast Damping means the resisting of movement at shaft speeds around and over 1m/s, generally. So basically, when you hit a bump, a pothole, a crease in the asphalt, go onto the kerbs etc.

Fast damp speeds are generally about half, or a bit lower of the slow damp speeds, but that's a very generic assumption. JDM aftermarket dampers generally run fairly high fast damping, for example, and can be over half of the slow speed, while I've seen fast damp speeds as low as 1/3 of slow damp speeds, in older OEM part equipped cars.

Fast damping is used to slow the wheel when it hits bumps, and to reduce oscillations when it rebounds from them. Fast bump, for me, is pretty much track/rest of car setup dependent and I'll mess around with them if bumps and kerbs cause instability or loss of grip.

Too low fast damp rates can cause violent chassis behavior, and too high fast damp rates can cause rapid unweighting and flight when hitting elevation changes.

That's it for now. Anyone who knows better, or in this case, can be arsed to write more than I did and go into more depth, is free to add anything. This is a very general guide that everyone should understand fairly well and should be able to use to make the car handle a bit closer to what they want.

I'll write more if this is received well/I can find the time and will.

 

Excellent,

.

Excellent, I haven't read it all but the first part about ride height was good enough for me to say thank you for your time. I look forward to reading more later.

 

well on other sim, by setting my car propperly I was able to cut over 2 seconds from the laptime (Road America) .. using the same (correct) line ... depends how good default setup is ..

 

Nice guide, thanks. Will surely be useful!

Just one question regarding the quoted text: are you sure that AC doesn't simulate aerofoil angle of attack? I thought that aero changed depending on the orientation of the wing. For example, when the car leaned forward under braking, the aero should increase. I know they even simulate dirty air, so such a thing seems rudimentary. Because, there's an Aero app, which shows the angle of front wing, rear wing, and undercarriage. I have not tested it, but it would make sense that these values change in real time...

 

@speedbee

I am not 100% up to speed on how AC's aero system works, so that statement I made could be incorrect.

AC simulates angle of attack of aero surfaces, that is 100% certain.

I was not aware of proper dirty air simulation between aero surfaces, though. If that is indeed the case, then my statement is wrong: total downforce should increase during braking, in the front and the rear.

 

i did some testing and it seems it does .. angel of attack increases under breaking and so does the drag of that wing ...

 

Oh, I worded my post badly. They don't simulate any interactions between front and rear wings. I know that there's a really simple simulation of front downforce loss when driving close behind another car. So, it's more like, dirty air can effect front wings. I'm guessing they just sort of did "if closer than 5m to car ahead, reduce front df by 50%" or something.

Still though, you are right this is quite important, and does warrant more testing, like @ouvert did.

 

Okay, so I was correct.

As I said, AOA definitely affects downforce: every sim since rFactor can do that IIRC.

What I was talking about was quite complex aero surface simulation that I didn't think AC's aero interface would even allow. Seems it doesn't.

Doesn't matter *that* much because AC is not the only one missing this, all sims are.

 

"On some cars like touring cars, this isn't so much a problem, while in GT cars you must run proper geometry, because you'll just bottom out with a low car, anyway. "

Why is that, what makes touring car suspension tick differently from GT car suspension?

 

thanks Arch,

Awesome post, very interesting read

Look forward to the next instalment

 

"The aim of art is to represent not the outward appearance of things, but their inward significance."
Aristotle - on why to use core temps

"The worst form of inequality is to try to make unequal things equal."
Aristotle - on simmetrical setups

"The aim of the wise is not to secure pleasure, but to avoid pain."
Aristotle - on overreving engines

 

https://www.assettocorsa.net/forum/i...t-setup-of-alfa-t155.25522/page-2#post-522451

 

@mistery

GT car suspension is designed for racing, while old touring car suspension is pretty much the same geometry as the stock roadcar.

The downsides of lowering the car were historically not deemed to be greater than the benefits of a lower CoG, better aero etc. and in AC it's about the same, the cars handle better even if the suspension is a bit messed up from the ideal geometry of the roadcar. The geometry is not 100% the same as the roadcar, but close enough to cause some problems when lowering, opposed to having a GT car that has a purpose built suspension.

GT cars' suspension geometry should work even down to 60mm, but I prefer to run about 65mm to 75mm due to the spring and damper rates I run in the GT3, GTC and GT2 cars.

There's more to it than that, and it's a per car basis, but basically, the downsides of running an old touring car very low isn't as great as running a modern touring car very low. You will noticed that if you run a GT car low and drive on the Nordschleife for example, you will bottom out with appropriate spring rates, so you need to raise the car, or stiffen a lot of things up which makes handling even worse on the bumpy, fast track.

Meanwhile, an FR layout 80's or 90's touring car with very little aero and outdated tires will not suffer much if it jumps when you go over kerbs, bottoms out when you hit bumps etc. because the car is nervous anyway.

This is mostly just my opinion and different race engineers will say different things, but I think this is accepted universally.

@next segment

I'll write one later today, on whatever topic I think I have down well enough.

 

I'm sorry guy whoever posted this, If you happen to make this pdf let everyone know or add to it. I tried looking for you but without luck.

Aero on the Lotus T125 S1, I tried using generous amount of rake. I kept spinning mostly on the exits, for a long time I thought casters along with weight distribution of that rake was causing it.. But it should understeer with lesser caster because of that higher rake.

If aero affects the front wings involving rake, then I should be spinning on brake turn in. Wing closer to the ground when the car dips hence better duffusion effect.. But I get massive oversteer on exit. Doesn't make sense for me

 

Tis will be interesting

@Arch "When tweaking the differential, start with 0 preload and 80% power/20% coast" WTF, why would you use near locked power diff and almost no coast, is it LFS 2.0? I always try to get as little power diff as possible without inside wheelspin. And from pure mechanics perspective having a highly locked diff will make the two rear wheels waste grip on fighting each other - and in game it can be felt with more oversteer.

And then 20% coast? Like in low speeds, where it actually matters the car already is oversteery in nature from stuff like: higher engine braking torques, possible brakes used, and other stuff like rear bumpsteers, camber changes, stalled diffusers etc all making rear starved for grip or at least overly sensitive - getting that almost completely unloaded rear inside to not lock is the name of the game for me usually.
If anything i try to start from the exact opposite - minimal power diff / medium to high coast diff.

Rest is pretty much spot on thou kudos.

also LOL Aris, getting down with Greek racing philosophy ... dis game needs more chariots.

 

@Nao

You're completely missing the point. You start with very extreme values and move more towards normality, rather than the other way. I find it a far more effective way of working.

 

@Arch Well ok, that would work. I guess im used to doing this the other way - start in the middle (or even better, on some expected value) and tweak once in one direction and if it's giving improvement, don't bother with the whole other side.
Plus you said "If you oversteer too much on the brakes or the throttle, increase coast or decrease power." - if the car didn't oversteer at that point, that would imply 80% power diff to be correct choice even thou it's more likely there is a miss in other setup values.

 

Thank you guys for these value information.
Just one question?
Is there a way, besides ingame sound, to know when a car is bottom out? Any ingame application or motec channel?