When the simulator software is installed, a folder named iRacing is created in your Documents folder. The first time you drive a specific car, a subfolder is created (called setups) and then in that folder other folders with the names of each of the car.s i.e. streetstock, audirs3lms, etc. Any chassis setup changes you make and subsequently save will be save to the corresponding folder:

If you are unsure which folder the setups for a certain car are saved in, the directory for each car's setup can be found at the top of the Load Car Setup Screen by clicking "Garage", then "My Setups" in the UI: