The Chinook originally had two small wheels per landing gear on the rear. When it went to the steerable rear wheel system the Single Wheels were installed in lieu of the double wheels. The much larger tire gives better handling.
The Chinook is fast for several reasons....sheer horsepower is one. Tandem Rotor systems are more efficient than single rotor systems as well.....no loss of power to merely counteract torque of the Main Rotor system.
Third....the top and lower thirds of the fuselage usually have some hydraulic fluid smeared all over them so it is slippery as an eel.
