@gekkoX We were told that they do intend to support control wheels:
I don't have a wheel to test with to confirm whether or not it currently works though.
We haven't seen any further announcements related to Stadia support for racing wheel input. I'd suggest using the in-app Feedback option to let the developers know how important racing wheel support is for you.
Don’t send in-game feature requests. Send them here and VOTE UP ideas you want.
This is the only way for users+developers to keep track off which issues have more votes and prioritize the right features.
Also, this could be added much faster if we had access to create our own controller configs and share them with other users (like Steam does).
Check out my idea bout this and please vote it up: