I am currently working on a Nascar game on the Unity3d engine.
The vehicle handling will be done using UnityCar 2.2 Pro.
You will be provided with the nascar vehicle asset.
You are required to tweak the UnityCar Parameters, to get the vehicle handling to feel like a nascar vehicle.
You can use this as a reference, how I want the car to handle.
This was built on UnityCar as well.