Welcome to GTSetups.com. This website was created during the Gran Turismo Sports Closed Beta to share your setups with other players and be able to lookup setups yourself to use.
Creating an account is free and enables you to share your setups with other people. There's also an option to generate images of your setup which can be used on other sites or forums, e.g. GTPlanet.
Now that the game has been officially released, the daily races are all under "Balance of Performance", so the car setups are limited to brake balance, traction control and sometimes tyre compounds. This means that the setups cannot be used for the daily races or the FIA championships but they can be useful in time trials and other events.
When the time comes when the demand for setups grows, I'll hope that this site will help.
Have fun!