This is a paid asset, but now you can download WheelColliderS for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
WheelColliderS v1.0.0
WheelColliderS is a complete alternative to Unity’s inbuilt WheelCollider. It allows for more realistic vehicle behavior, complete customization, and 3D ground detection. 1D ground detection is the past, WheelColliderS provides 2D ground detection at the lowest setting. With WheelColliderS you can make your car runs on very thin objects or runs upside down.
Wheel has width, not only a single ray down.
2D wheel at the lowest setting, you can make your car runs upside down.
API not very different from Unity’s inbuilt WheelCollider so it is easily swappable.
Fully customizable via the custom inspector. Adjust spring, damper, friction curves, geometry, etc.
Adjustable camber angle, toe angle, and wheel offset.
Pacejka friction model with support for different surfaces.
Friction preset system that uses one ScriptableObject with enum for easy setup.
Fast ground detection.
Adjustable at runtime.
Can handle wheel visuals by itself (position and rotation).
Easy to set up.
High performance (my i7-4600M can runs 70 cars, each car has 4 fully 3D wheel with ground detection at 60FPS).
Full C# source code included.