Wednesday, September 23, 2015

The Great Window Debate: Does Driving With the Top Down and Windows Up Save Fuel Economy?

Does driving with your windows up when the top is down really save you gas mileage in your convertible? Some confusion and debate continues on the subject—like boxers or briefs, or why do you press harder on the remote when you know the battery is dying?

At lower speeds, the added wind resistance from turbulence created by an open roof isn’t that great. So there’s little to no penalty for city cruising. However, if your convertible top is down on the highway, you’re going to be paying for it at the pump. Some have found a 14 percent hit.

Manufacturers maximize fuel economy for the condition the car is in most. Odds are the vehicle will have its top on more often than not. Also, when you remove the roofline, you have more area—more room for the air to get recirculated back in to the vehicle and reduce aerodynamics. Larger convertibles with bigger cabins (like four-seaters) could experience a greater loss in fuel economy.

When the top is down, you’ll get slightly better gas mileage with the windows up, the difference is only marginal, as reported by Car and Driver. Moral of the debate: If you’re really concerned about fuel economy and you’re taking a long trip on the highway, consider driving with your top on. Otherwise, enjoy going topless (the car, that is).

Here are some other ways to maximize your fuel efficiency:

  1. Drive smoothly: Aggressive driving wastes fuel—especially at highway speeds. So accelerate smoothly and brake softer and earlier. This can save fuel and also prolong the life of your brakes and tires. 
  2. Slow down: Speeding wastes lots of fuel. Your fuel mileage decreases rapidly at speeds over 50 mph. That equals paying an additional 26 cents per gallon for every five mph above 50 that you’re driving. 
  3. Only use A/C on the highway: Your fuel economy drops when you use the air conditioner at low speeds—by up to 15 percent. So if it isn’t too hot, turn off the A/C around town and roll down your windows instead. However, at 55 mph or higher, using the A/C is preferable to open windows for two reasons: Your vehicle has much lower wind resistance with the windows closed, and because the engine makes more power at higher revs, it’s able to run accessories like the A/C compressor more efficiently.
  4. Stay in gear when stopping: While shifting into neutral and coasting to a stop sounds like it would save fuel, the opposite is true. Many modern fuel-injected vehicles go into a “fuel cutoff” mode when the engine senses that the vehicle is in gear, the rpm is above idle and the throttle is closed. Shifting to neutral may cancel that mode, so keep it in gear.


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