Yeh aerodynamics can make a huuge difference on fuel consumption. Whenever anything travels through air it has to produce enough force forwards to counter the drag, which is the force caused by interaction with the air that tries to slow you down. With a worse aerodynamic shape, the drag force is larger which means the forward force has to be larger to overcome it. This means the engine has to work harder to produce that force, and therefore use more fuel!
Three interesting facts:
1) If you were to drive to Scotland from London, it would take about 2 full tanks of petrol in a normal car. If you put a bike on your roof (ignoring the extra mass of the bike), the drag caused by that bike would mean it would take 3 tanks of petrol!
2) The aerodynamic design of the back of the car is just as important as the aerodynamic design of the front of the car. Drag isnt just caused by air hitting the front of the car, but also by the air behind the car “sucking” it backwards!
3) Lorries drive really close behind one another on the motorway to save fuel. The lorries behind the front lorry are effectively “hidden” from the on coming air so experience less drag. They take it in turns to go to the front so everyone gets a turn at saving their fuel.