Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download Motorbike Starter Kit Free.
Motorbike Starter Kit v2.1
MSK is a new package which is designed for Motorcycle Games that would give you the ability to work and hand it easily.
Features of this package :
* Cameras are all set fine and The views can be easily changed and shifted
* Motorcycle controls are all real that would give you the real sense of driving
* This package is easily manipulated and edited
* Brake lines and particles are perfectly used in this package
* The bike include shifting system
* The asset include mobile control (UI)
* MSK for Unity 4.x UI included
* Three different motorcycles