Which produces less wind drag?

Question

Which produces less wind drag, sunroof open with windows open or closed?

Answer 1

Your car travels in a slip envelope of air streaming around the curves of the car from the front to the back as you drive. It's better to have your car cut smoothly through the outside air rather than entering the car and creating turbulence in the air stream. When you open the sunroof, you disturb that air flow creating slightly more drag on your car. Opening your windows creates even more drag, because there is greater disruption of the exterior air flow.

If the sunroof is open, having the windows down produces more drag as you drive. The open window causes more swirling in the exterior air stream. Outside air enters the car through the open window, and crashes into the seats and the back window. Driving with the sunroof open and all the windows open will have a parachute effect in catching outside air against the roof, back seat, and back window, and slowing the car.

Some sunroofs have a small air dam, or deflector in front of them to send air streaming over the opening. Some sunroofs can tilt up deflecting most of the air up and over the opening. When the air is deflected, additional drag is minimized. This deflected flow can actually pull air out of the car as you drive. This will create uncomfortable changes or oscillations in pressure. In this case, it's better to open a window, at least a crack, especially when driving at higher speeds. Having a window open just a crack doesn't lessen the drag created by opening the sunroof, it creates slightly more drag, but makes driving easier by easing the fluctuations in pressure.

While driving with windows open in your car increases drag, the amount of drag depends on the design, type, and model of car. Stock cars drive with open windows, but these cars are designed and shaped to compensate for the disturbed air flow around the car, and minimize it's effects.

The majority of drag on your car is created by friction between the tires and the road. Opening your sunroof, or opening your windows increases air drag, but more drag is found at the grill of your car as it pushes straight through the air in front of the car as it moves forward. Especially in stop and go city driving, having the sunroof open, and the windows open will have an effect, but it is not the major factor in slowing the car. In modern cars, increased air drag from open windows, is not much of an issue with speeds under 30-35 miles per hour. The drag could have a measurable impact on gas mileage when traveling at higher speeds.

Answer 2

If I am reading it right the choices are 1. Sunroof open /windows open .or 2. sunroof open windows closed? if this is the case it's #2 sunroof open with windows closed.Rule of thumb is more sealed cabin is better. To prove the theory you can conduct "COAST DOWN TEST" ,get a stop watch and a smooth straight road and get going a certain speed and slip car into neutral and time the speed reduction bck to a preset speed ,do this under both conditions and in both directions to compensate for wind ,this method is a "POOR MAN"S WIND TUNNEL"-hope this helps

Answer 3

All closed. If your driving down the highway, think of your car as a parachute that catches the air and slows you down. If it was all open, you reduce the aerodynamics of the car and increase drag and fuel consumption.

Answer 4

Depends. If you have the roof up and the windows up there will be very little air. Nut if you're going to have the roof open it's probably windows down.

Answer 5

windows down to allow air flow