Detail this asset from Unity Asset Store: Original Link
This is a paid asset, but now you can download Kart-Racing Physics Free.
Kart-Racing Physics
Kart Racing Physics provides an easily tunable arcade-style physics simulation in the vein of classic racing games.
Try out the Web Demo to see how it plays.
Features:
* Fully Updated for Unity 5
* Simple to setup – simply swap in your own models and be ready to race in no time
* Easy to tweak – no complex torque curves or tire friction values, just adjust parameters like top speed, acceleration, traction etc to create just the feel you want
* Built-in support for arcade-style powerups – easily give the vehicle a speed boost, make it spin around and slow down, and several other simple to use effects
* Fully documented C# code – clear, readable and easy to modify
* Fully working example scene with race-track and powerups