To get your wheel automatically detected as one, as well as rebinding menu and flashback controls you need to edit one of the game's default wheel control presets.

• Navigate to the game install folder.
  
  • Right click on GRID in your library => Properties => Local files => Browse local files
• Open the ActionMap folder
  
• Open actionMapPreset1.xml in a text editor (Notepad or Notepad++ for example)
  
• At the top of the file replace "Logitech G25 Racing Wheel USB" by the name of your steering wheel.
  
  • You can find that in the Game controllers control panel item in Windows.
• Customize the rest of the controls to your liking
  
  • You can visualize button numbers in the Game controllers control panel
    
  • Take note that button numbers in the xml start from 0, so windows button 1 would be win_con_di_button0 and so on
    
  • If pedals are inverted, try other values of baseCalibration
    
  • I recommend deleting slider0 references
    
  • To unbind a control use axisName="unmapped" (useful for Gear actions if you have no shifter)

For my T300RS I use this actionmap: https://pastebin.com/raw/MHiUSYY0

This is an optional step that may help with fine tuning FFB for your wheel.

• From game install folder, open forcefeedback folder
  
• Open devicesetup.xml in your text editor
  
• Edit a line with the name of your wheel
  
• Tweak settings as desired

Finally you will need to change some in game settings for the game to drive properly. Being an old arcadey game with wacky physics, GRID only really works with 180-200 degrees steering lock.
While you can change that in your wheel's software, setting steering saturation to 20% or 25% does the job just as well so do that.
Remember to keep sensitivity on 0 and remove any steering deadzone the game might have added.