First you will need 3 monitors set at the same resolution. It is recommended, but not required, to have three monitors of the same make/model, though screens that are the same size will work. It is NOT recommended to have three different sized screens as it will be difficult to get the screens to line up properly.
Certain NVIDIA cards can support 3 displays using a single NVIDIA graphics card. Plug in all monitors to the NVIDIA graphics card and be sure that they are connected.
Make sure to download the most up-to-date drivers for both your graphics card and your version of Windows (7, 8, or 10 — make sure to select the 64-bit option if you’re on a 64-bit version of the OS).
Right click on the desktop and select NVIDIA Control Panel.
Once you have the NVIDIA Control Panel open, select Configure Surround, Physx in the left hand side to open the configuration options.
Put a tick in the Span displays with Surround box and hit apply.
Then select 1x3 in the Topology drop down.
Then select the highest resolution in the drop down.
Arrange the numbers as there displayed on your monitors.
Select “Enable Surround.”
Once this has been enabled go back to the iRacing UI and click your helmet at the top right and
Then Launch "Run Graphics Config –Launch”
Select "Auto Configure"
Then select the highest resolution in the drop down to match the resolution in your NVIDIA Control Panel.