"Effect of Windows Down on Vehicle Fuel Economy as compared to AC load." July 13, 2004. "Gas Pains: Mileage Myths and Misconceptions.". "Will rolling down windows save fuel or not?". No matter which method you use, practices like keeping tires properly inflated, trimming excess cargo weight, and regularly maintaining driveline components will likely see greater benefits to fuel economy. Every vehicle will behave differently, so there aren't many hard rules. Really, the benefit or hindrance posed by driving with windows down will depend on a number of variables, like vehicle shape, engine size, and compressor efficiency. ĭriving with the windows up and the AC off might be the most fuel-efficient way of all, but who can do that on a hot day?
#Mini mog truck driver
Car and Driver did its own study and determined that you should switch off your air conditioner - most of the time. With smaller vehicles, like the Corolla, you could use the AC and get up to 70 to 80 mph (assuming that's a speed limit where you are) without using extra gas.Īlthough we've made the case for both windows down and air conditioning, some argue that the windows down option is still the better bet. If you're searching for a good rule-of-thumb number for when it's best to open the windows and switch off the air conditioner, the cut-off should be around 40 mph (64 kph) for larger vehicles. So even though the vehicle's speed is doubled, the drag is actually increased by four times. For example, when your vehicle is traveling at a speed of 70 mph (113 kph), there's actually four times more force on the vehicle than when you're cruising around at 35 mph (56 kph). But the drag doesn't increase in a linear fashion, it increases exponentially. Īs your speed increases, however, the amount of drag on the vehicle will also increase. When the engine is operating at faster speeds, it's already producing ample power for both the engine and additional equipment. What's the reason? Well, at low speeds your engine is producing less power, so it would have to work much harder to power accessories like the air compressor (for the air conditioning). The study concluded that the more aerodynamic the vehicle, the more drag open windows will create. These differences are an important factor in determining just how much the windows down option will affect the fuel efficiency of your vehicle. įor the sedan, when the windows were down, the efficiency was reduced by 20 percent, while the SUV fuel efficiency was reduced just 8 percent.
Overall, both studies showed that driving with the windows down has a significant negative effect on the fuel efficiency - more than using the vehicle's air conditioner. Two vehicles were used in the test, one was a full-size SUV with an 8.1-liter V-8 engine and the other was a full-size sedan equipped with a 4.6-liter V-8 engine. In the desert, temperatures and vehicle speed were factored into the study. In the wind tunnel, air was forced over the front of the car and also from an angle on the front of the car to simulate a cross wind. So, does drag really affect a car's fuel economy more than air conditioning? There are times when using the AC will save you gas.īack in 2004, the Society of Automotive Engineers (SAE) conducted a study at a General Motors wind tunnel and on a desert track. Unlike the parachute, you definitely don't want a lot of drag on your car because it makes your engine work harder to get your vehicle up to the same speed. When a skydiver opens up the parachute, it cups the air and causes a massive amount of drag, enough to slow the speed of the skydiver and allow him or her to land safely on the ground. You can think of it a bit like a parachute. However, when a vehicle has its windows down, air passes into the car where it was formerly allowed to flow over it, causing resistance that didn't exist when the windows were up. Most modern cars are designed to be relatively aerodynamic, which allows them to pass through the air with minimal resistance. Drag is the resistance that cars, and all moving objects, encounter when moving through the air at any speed. The second is what is known as air resistance or drag. The first deals with how the air compressor in your car works and how much extra fuel the engine has to use to keep it running. There are two main factors to consider when approaching this question.
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