So I launched my game and my controller would not work in-game at all. I discovered the problem prety quickly since it's not the first time this particular issue has plagued me in a game. First off:

Do you have another peripheral connected such as a joystick or steering wheel attached to your PC? Try just disconnecting them first and trying again.

In my case and perhaps yours too is that it's something a little more sneaky. I have a ROCCAT Tyon mouse and it has an analog throttle fin on the side which Windows detects as a USB game controller.

You can disable this simply by going into Device Manager and looking under Human Interface Devices and seeing if there is more than one HID-compliant game controller on the list. You can try and see which one you need to disable by right clicking on one then going to properties and then under the details tab find the drop down box and select Hardware Ids. Once you have that open go back to Device Manager and look for your game controller you're trying to use - in my case it's a wireless 360 controller so it's under Xbox 360 Peripherals. Once you find your device do the same thing as with the HID one and look at the Hardware Ids and see if they match. If they don't and you have nothing else connected to your PC go ahead and right click on the offending HID device and disable it - you could uninstall it as well I suppose but normally they disapear when disconnected and so it may just try and re-install itself after uninstalling it if the offending device is still connected.

After following those steps just make sure your controller is conencted before launching the game from Steam and you should be good to go! Happy gaming! Now if only we could get 60 fps and 21:9 support on this game.

Note: The throttle control should actually still work in other games if you're using the up and down motions of the throttle as hotkeys selected in ROCCAT's software.