I do not have Project Cars but every game since GTR2 (I did not have GTR) has used the same setup system/terminology. Matt Orr (Empty Box) stated in his PC review of pCars that car setup is the same as GTR2 and the standard that everyone understands and uses, meaning if you were to talk to any legitimate race engineer IRL these would be the terms they use and understand.
In fact for GTR2/Race07/GTR Evo you can export the car telemetry and use MoTec analysis software with your preferred project worksheets to set up your car. Actually you could take your exported file to a legitimate race engineer and have them help set it up if the analysis software is MoTec or supports MoTec format import. For more in depth coverage of this topic look into
this thread.
Anyway since I do not have pCars I am going to talk a little about GT cars in GTR2 so I hope what Matt said was correct (and it may only be true for PC?).
Softer should mean more grip unless something else is horribly maladjusted already (car body or suspension bottoming out for example), softer spring rate, softer ARB setting, or softer tire compound . Less front spring rate and/or ARB will grip more in the front for example. Ideally run the softest setup that uses the maximum travel range possible without topping or bottoming out the suspension or car. However, this is totally driver dependent because a slow driver might hit a particular bump or dip at 100 mph where a fast driver will hit it at 130 mph, the faster driver will need stiffer springs and shock settings because they are experiencing much higher forces from that bump or dip.
It is important to understand what adjustments are main tuning and what are fine tuning. Springs are for main tuning. Anti roll bars (ARB) and tire pressures are for fine tuning after spring rates are correct or near correct. Often I see people changing tire pressures when tires are getting overworked (too hot), however the true root cause is incorrect spring settings. Changing spring rate settings produces large changes in grip, more grip always means more heat. At some point the balance between grip and heat have to meet in a happy middle. Springs first, ARB next, tire pressure last.
In a perfect world that last tire pressure adjustment should only need small tweeks to balance tire temperatures across the tire. Balance does not mean the same, it means linear progression, for example if inside->145, middle->145, outside->135 try lowering pressure to get 145, 140, 135. If tire temperatures overall are too low or high then you may be under or over driving the car (or using the wrong compound) and may need to start over with a lower or higher spring rate baseline. Remember the bump and dip example above? If a fairly well set up and balanced car is driven too timidly it will oversteer badly and the opposite, driven too aggressively it will understeer badly. Sometimes the problem is not with the car setup but with the driving, again the setup and driving need to meet in a happy middle. A pro sim racer talking about using MoTec data to realize he was driving too aggressively for the car setup:
www.youtube.com/watch?v=d2ur0L0LDOw&feature=youtu.be&t=960Ideally keep the car as low as possible without bottoming out. At some point a compromise has to be made between spring stiffness, ride height, and keeping the car bodywork/frame/tub from bottoming out. Usually if a compromise has to be made, favor raising the ride height in order to be able to run a softer spring setup. Common sense needs to be used as well though. For example setting up the car for one extreme section on a track which then slightly compromises it for nine other sections might result in slower times overall, or the opposite. For example Spa, because the extreme section is followed by the most important straight on the track it almost always makes sense to compromise every other section in favor of carrying speed up the hill out of Eau Rouge.
The shock fast bump (compression) and fast rebound must adjust up and down in direct proportion to the spring rate (stiffness) going up or down. Otherwise the cars wheels will become over or under damped going over bumps. Under damped is dropping a super ball on the ground, it just bounces and bounces. Over damped is throwing a dandelion seed into the air, it goes up but takes forever to come down. Critically damped is like throwing a bean bag into the air, it goes up and comes down fairly fast and lands with very little if any bouncing. A critically damped suspension has the tire in contact with the road surface and working the hardest for the longest time.
Fast shock adjustments are for keeping the wheel/tire in contact with the track and slow shock adjustments impact the car body attitude: body roll in cornering, and/or diving and lifting under braking and acceleration. Imagine viewing a car from the chase cam (normal GTA view meaning not first person view). Under damped would be the super ball thing again, in a right hand corner the car would roll WAY too far onto it's left side, come crashing back down WAY too hard, causing it to bounce back up onto it's left side too far, etc, etc. Over damped of course would be the opposite, the car rolls onto it's left side but the corner apex is done and behind but the shocks are still SLOWLY lowering the car into a neutral attitude while the front left tire is slowly being cooked.
The unfortunate thing about all that shock stuff is that without some sort of proper telemetry tools I do not know how these can be set near correct. If they were GROSSLY far off perhaps they could be improved just from watching and feeling the car behavior. Normally the best we can do is have faith the baseline setup is correct (unfortunately in GTR2 it was hardly ever close to correct) and increase both fast shock setting a bit when spring rates go up and decrease a bit when spring rates go down. Probably never need to mess with slow settings but slow settings are very important in some specialized situations especially in something like NASCAR (stock car/circle track) racing.
Camber, run as much as possible without destroying tires. Not the ideal solution but easy to understand and implement. High speed straights want little camber to prevent excessive heat buildup on one side of tire. In corners at peak load you probably want more than you can physically get from the car setup limits. So it is always a compromise on a normal road course. Understanding the requirements, strengths, and limitations of all the choices helps chose settings. Again a bit driver dependent as a slower driver might not be able to generate enough peak cornering forces to run full camber setups but not a big issue like spring rate is.
Caster, driver preference. For example Monaco run low caster (quick steering response but twitchy at speed) LeMan run high caster (nice and steady, no surprises but at the cost of slower steering response). If using a controller and the steering feels twitchy running more caster might help.
Toe, same as caster, driver preference. If you can not decide run -1 (or zero) front and +1 rear as going too far positive or negative starts to impact straight line speed. Negative front toe gives better turn in but maybe worse mid corner, can be twitchy at really high speeds. Positive front toe gives good high speed stability but maybe less corner entry crispness. There is no guideline for what toe will do at the rear, it is trial and error on a car by car basis although lots of people will disagree since they (correctly) know how it reacts on one type of car, GT cars for example.
Other stuff, third spring, bump stops, ARB preload, etc. Anyone at a level where this kind of thing would actually matter should be way beyond where I could say anything to help them.
Brakes, braking is highly over rated. But all joking aside, Keith Code is famous for his
no brakes no shifting exercise he uses in his motorcycle training schools. Try running some laps no brakes with the goal of getting faster and smoother over quite a few laps. Then add in brakes the same way a little at a time to see what happens.
