I was going to write some explanations here, but eran0004 has it well covered! I do have something to add on brake bias.
Brake Bias
I usually drive FR cars and often put the brake bias a little rearwards as:
i) It helps the car turn in on corner entry when trail braking (mild oversteer). Many cars on factory settings understeer a bit too much for me.
ii) For events with tyre wear, the front tyres tend to wear faster as they are taking a lot of the steering and braking effort. This applies even to FR cars where the rears are doing the acceleration. Once worn, you get more understeer so it helps to add rear brake balance at the start of the race and/or as the wear occurs to both eliminate the understeer and equalise tyre wear, the tyres last longer between pit stops that way.👍
iii) Note that when you change brake balance, then press the brakes, the top of the braking indicator bar will be red. The more extreme the balance adjustment, the more red. This is similar to the throttle bar when you use traction control. I assume this means the red part of the brake is
not used. You are reducing brake pressure. The brakes are overall weaker, but you gain a more favourable balance of car handling. This can still make you faster overall.
The units of force and exact numbers below, are fictional, but I think it works like this, where changing balance always weakens one brake, rather than strengthening one. Adjust rearward and you don't get more rear brake, you get less front brake.
e.g. Brake balance 0 F 100/R 100 Overall 200
Brake balance 2 Rear F 80/R 100 Overall 180 but more oversteer
Brake balance 2 Front F 100/R 80 Overall 180 but more understeer
I also think most front brakes start as more powerful than the rears (this is true in real world). I have put them both as "100" just for simplicity. But it might actually be more like "F 150/R 100 Overall 150", as default.
I drive without ABS and look to lock up the front wheels under braking, then adjust rearward until I get the handling I like. If I can't lock up wheels any more then I know I've sacrificed brake performance. This is tyre/car dependent. I haven't tested but a stock VW beetle on RSS tyres probably will notice a reduction in brake performance since the tyres are so sticky and could cope with lots of brake force. A Group1 race car on Comfort Hards (lol) may have such good brakes, and such poor tyres that reducing brake pressure by moving the balance still means the crappy tyres can be locked up, so no loss in performance (the tyres are the limiting factor).
@ekhlious , if you want to learn more about suspension tuning in general, check out Scaff's GT4 guide and Motor City Hami's GT5(or was it 6?) guide. These are available in the relevant GT games' Tuning forums and most will apply to GT Sport.
GT Sport has practically no telemetry so it's hard to tune numerically, you have to do it by feel (and lap times!). It requires patience. I'd advise spending quite a lot of time on your favourite car, and always run several (I usually do 5 or even more) laps after changing a setting, use a short track so you're not there all day, I like Tsukuba. You need repeat laps since there's always human variation and it's easy to mess up/absolutely win on a single lap and put it down to the setting when it was just luck. This is "boring", some people hate it and others fall in love with the detail and the car, looking to shave another 0.2 seconds off their personal best.
Keep old tunes in different tabs, that way you can go back to them if you mess something up. Sometimes after tuning a while you'll actually go back to an old tune and be faster as your driving style has evolved. When you're tuning the car for a long while, the car also tunes you