Racing bikes are designed to propel you as fast as your legs can power you on the road.
To achieve this, road bikes are as light as possible, with 'drop' handlebars lower than saddle height which seat you in the most aerodynamic position to reduce drag. The gear ratios are usually positioned closer together, to allow pedalling at the most efficient speed.
Wheels rims are also shaped to maximise aerodynamic efficiency, using light aluminium alloy or carbon fibre to cut weight and you'll often find a reduced number of spokes which may be bladed to reduce drag even more.
Tyres tend to be very light and narrow to reduce wind resistance. The tread is usually fairly smooth to reduce resistance from the road.
