Shut that Window

While we are on the topic of Drag, one of the side effects of doing something as simple as opening the window while you are driving is to increase drag and influence your fuel consumption adversely.

Again it's worse at higher speeds, the turbulence experienced if you drive at high speed on a motorway with the windows open is such that normal conversation becomes impossible. This turbulence is creating an invisible envelope of disturbed air around the car and increasing drag.

Funnily enough this turbulence is a good thing because when the noise from the window becomes too much, such that you cannot hear the radio, you shut the window.

So this tip is:

Shut that Window

However there is more to this than first meets the eye!

As I pointed out earlier the motor manufacturers are spending fortunes on their study of car aerodynamics. Because modern cars are more streamlined and aerodynamically efficient, the drag created by opening the window is proportionately more than if the car is an older, less aerodynamic design. If your car is a "boxy" design then opening the window at low speed is unlikely to cause a large increase in your fuel consumption, whereas if you drive a streamlined arrow then the increase will be larger as a proportion of that car's base aerodynamic efficiency.

So what we have is a more complicated set of alternative scenarios:

If you drive a box then at low speeds having a window open is going to have little effect.
If you drive a box then as your speed increases your drag goes up and your fuel consumption will rise, so shut the window.
If you drive a streamline model then having a window open, even at lower speeds, will have a greater effect proportionately on your fuel consumption.
Then if you drive your streamlined model at higher speeds with the windows down then you have undone all the work the manufacturers and their engineers have put into the design and your fuel consumption will soar.
However (isn't there always a however!!) another factor must be considered which brings us to the next point: