Hello, as the title suggests, I’m trying to make a car in unity, and just added the wheel colliders. However, when I did that, the car flipped out and goes flying. I did a google search to find similar problems, and the solutions I found did not work. I tried going into the project settings, and changing the gravity from -9.8 to -20. I also ensured that my car’s rigid body has a mass of 3000. Can someone shed some light as to what I’m doing wrong? 
Thank you!
Alright all, I fixed the problem, but I’m not sure exactly what it was that I did to fix it. So for future reference, if anyone is reading this post, these are the steps I took. I went back, and deleted all of the wheels except for one, and re-added them into an empty game objects(centered around the car) and placed them all in them. Then, I duplicated all of the wheels, but deleted the duplicates actual mesh, leaving just the empty game object that is now centered at each tire. From there, I simultaneously added wheelcolliders to the wheels, and adjusted their size to fit the car. And voila, my car no longer floats, and with my added script can drive.
You should check if another collider from your car collides with the wheel collider. It was the problem in my case.
I encreased the mass value of the car - parent of wheels