Please explain the relationship between Diameter of the Wheel and the Turning Radius of the vehicle.(Car or Bus). Does the length of the vehicle also matters.
There is no relationship between wheel size and turning circle - the turning radius of the vehicle is defined by the geometry of the front suspension, and the wheelbase and overhangs of the vehicle.
For example, the traditional London Taxi is famous for having a very small turning circle, as it is designed to cope with very narrow streets. This is achieved through clever steering design - it uses the same size wheels as most other similarly sized cars.