Steering Response - It sets how fast you can steer. I would recommend setting this to be quicker than the default setting. If you play with precision, you can be daring and try the Quick 15 setting. If you want to laugh at how slow the steering can be, try the Slow 15 setting.
Acceleration Response - It sets how quickly the power of the car will be used. The slower setting makes weight transfer to the front much slower, while the quicker setting makes the transfer quicker. Set this based on your preference.
Brake Response - This setting sets how quickly the brakes are used. The slow response will make the brakes take longer to reach strong braking and lasts long after you stop pressing it and if you set it to be quick, you will instantly have braking power. Again, this is up to personal preference.
Sets the braking power on each side of the car. Setting the brake balance to the front will have strong front brakes and setting the brake balance to the rear will have strong rear brakes. I wouldn't recommend being extreme with this setting unless you want an out of control car every time you brake and/or longer braking distances.
Lowering the front and rear will make your car more responsive to turning and raising the height on the front and rear will do the opposite. Raising the height of the front creates less response on the front, causing a tendency to understeer and raising the rear will create a tendency to oversteer.
Depending on the transmission level or car, you will be able to customize the gear ratio of 5-6 gears including the final gear ratio. Setting the gears to HIGH will make the gears longer and setting the gears to LOW will make the gears shorter. The preferred gearing setting varies between each car, power and even the installed transmission. You only get peak power and torque to work. You can find it in your car data which you can find under DATA -> CAR when you have autodrive on or opening the spec sheet in your garage. Generally, the gears should be in the powerband which starts around peak torque and ends around peak power where you should shift into the next gear.
In this case, 6700RPM is the peak torque and 7600RPM is the peak power. One thing I would recommend if you care about being fast on standing starts is to make your 1st gear short so you accelerate fast, ecpecially in a high-powered, turbo car.
Hardening the spring rate will make your car more responsive by reducing body roll. Harder spring rates to the front will bring oversteering tendencies to the car and harder spring rates to the rear will create understeering tendencies.
Similar effects from the suspension spring rate apply here. I would also recommend similar settings to the suspension too since you can lose the upsides of your suspension settings with very different damper settings.
Increasing the turbo boost will increase power of the car, at the cost of losing car condition faster.
This section is arguably the most important for your car. Each bumper level creates a more responsive or stable car depending on the aero part.
Front Bumper - A higher front bumper level creates more downforce on the front. Often when cars have issues with oversteer, this is the part that first gets changed.
Rear Bumper - A higher rear bumper level creates more downforce on the rear. The rear downforce provides more car stability with the rear of the car swaying less.
Bonnet - The higher level bonnets reduces the weight of the car, making it more responsive.
Mirrors - The higher level mirrors have less drag, creating a small change in handling and top speed.
Over Fender - Over fenders are meant to keep your car more stable. The effectiveness of the wider fenders depends on the car.
Side Skirt - The higher the level of the side skirt, the less drag overall.
Rear Spoiler - A higher spoiler level creates more rear downforce and more drag onto the car, impacting top speed. Not as effective at creating rear downforce/stability as the rear bumper, but it's important for a stable car that doesn't need to slide around the corners to be quick.
Grill - Customize the grill of the car if available. Higher level grills have less drag.
Lights don't affect car characteristics, equip whatever you think is good.