As with all options in Project Cars, there are many when it concerns using a gamepad, i'll try to explain a few.
Stick input is handled in different ways with the input system of Project CARS, input speed can vary between
Simply steering with the stick (Steering)
Moving the stick from side to side (Crossover)
Releasing the stick (Center)
The Crossover is there mainly to speed up the steering so that fast corrections can be made, it can potentially be cumbersome if there is tendency to over correct.
In case you find yourself correcting / swerving too much, just releasing the stick can be of use.
In the advanced options there is also an opposite lock help; this setting applies the Crossover speed in grip loss situations and it also gives you full steering lock.
If you are prone to correct too much, i would advice to turn this setting off.
There are 3 input modes and they behave a bit differently, even when all the menu options are set the same.
Atm, mode 1 has a different deadzone implementation, it can be set with a fairly high deadzone while mode 2 and 3 are best set according to how firm your analogue stick is.
(Less deadzone with a new pad, more with an old one, probably different between Xbox One and PS4 etc.)
You will have to experiment between the modes to see which steering speeds (and standard adjustable settings) you prefer.
The steering sensitivity concerns the linearity of the analogue stick, the more sensitivity you set, the curve will become more linear from the center.
Setting a value of 0 will make it most gradual from the center. This curve can be further modified by using the car setup options.
Every car has it's own (real) steering lock yet the steering ratio can be tuned to preference, this could theoretically make the sensitivity curve more gradual.
The setting is under the 'Alignment' tab and can be set to 'slowest' (all the way to the right) without much issues when using a gamepad.
Throttle and brake work in a similar fashion when it concerns deadzones and sensitivity.
Speed sensitivity reduces your steering lock at a certain speed, making you able to move the analogue stick fully to the side without disastrous results (usually).
You will have to find a compromise between being able to give full analogue stick input and being able to make a turn (at speed off course).
If you use a cockpit view with a visible wheel i'd suggest to try and use lower speed sensitivity and use the steering wheel to gauge the amount of input you need to give.
Naturally, because Project CARS is an advanced simulator there are also visible cues and cues from the FFB to gauge your driving .
(Currently, using an Xbox One controller on the PC can cause the FFB to become distorted, it's a know issue and being worked on.
setting Force Feedback to 0 is a temporary solution. Steering can also 'hang' if you move the stick from side to side in rapid succession,
this is usually not an issue when driving normally and releasing the stick will "unstick" it).
There is also a 'Controller Filtering Sensitivity' setting which filters out a certain part of what you're doing with the analogue stick.
Setting this to 100 does not filter out all of your inputs yet at that point inputs will have become a bit unresponsive, settings up to 85 should still leave some fidelity.
'Soft Steering Dampening' is there to smooth out / dampen the input while retaining fidelity although a certain sense of "directness" can be lost.
It appears that there are very different driving styles when using a pad; the Forza/GT chase style driving with a lot of speed sensitivity,
the 'glued thumb' style people who prefer direct control (and of which i wonder how their thumb doesn't cramp up), people who tap the analogue stick etc.
This makes for many different preferences to cater to and it can make it difficult at times to gather what people expect when they have issues with the controls,
there's a lot of adjustability but not everything is possible.