I have to admit, some cars look cool with a nice roof rack on top, and it’s a great way to let the world know that your winter weekends are spent at fancy ski resorts, not putting up the storm windows.
Just as most SUVs never go off-road (about 90 percent of them), most roof racks spend nearly their entire lives naked, but you’re paying for the privilege of having it. Just as the unnecessary all-wheel-drive on your bitchin’ Bull Durham Trailmaker robs fuel economy, so too does the rack—by increasing your car’s aerodynamic profile.
This stuff has actually been quantified. Lawrence Berkeley National Labs did a study that accused roof racks of consuming 100 million gallons of fuel in 2015, or 0.8 percent of all car and light truck gasoline consumption. The impact will probably get worse, because the accessory is proving popular—whether or not anyone actually needs to carry stuff or not.
Actually, aren’t people buying humungous vehicles again because they want space to move goods inside the vehicle?
The Berkeley study found that the rack’s drag impact can be anywhere from zero to 25 percent. And collectively, by mounting roof racks we’ll use 0.00001 percent of the time, we will, by 2040, be erasing fuel gains amounting to six times the savings from the fuel-cell cars on the road, and 40 percent of the battery electrics.
The smart thing would be to have the rack in place only when you’re using it, but most people don’t bother taking them off. How many people do you see driving around locally with those huge storage pods on the roof? It would help if manufacturers made them easy to mount and dismount, the researchers say. They also like the idea of requiring they be labeled for their energy consumption.
Along these same lines is a MetroMPG.com report that tested the effects of a rack—unloaded and with a mountain bike—on the roof of a very efficient economy car (a ’98 Geo Metro/Firefly with a one-liter engine and a five-speed). The Metro went from 55 mpg (with no rack) to 40 (with the rack and the bike). “I would never have predicted the fuel-economy hit would be so big,” says the self-proclaimed fuel-economy geek who runs the site. A friend tried using the rack on his Toyota Yaris and got even more dramatic results.
Obviously, the smart move is not to carry stuff in the car unnecessarily. You don’t need to be driving around in August with a giant bag of sand in the trunk. I once had a roommate who carried around at least a year of yellowing New York Times late editions, leaving only the driver’s seat uncovered. But the Times is available on the Internet.
And while we’re at it, we might as well address the old “windows up, windows down” controversy. On a hot day, is it better to drive with the air conditioner off but the windows open, or vice versa?
A 2004 Society of Automotive Engineers (SAE) study (conducted in a General Motors wind tunnel, and on a desert track), concluded the windows up, air-on scenario is usually more fuel efficient (even though the AC has its own penalty). The effect is speed dependent, though. Above 55 mph (and why are you driving so fast?) there’s a 20-percent efficiency penalty for having the windows down. At 25 mph around town? Leave the windows down and switch off the AC.
Some other ways to become a fuel-economy champ:
Drive efficiently. Can the jackrabbit starts, and jerky braking cause you to waste fuel? I once did a test—driving like an idiot with sandbags in the trunk, and driving responsibly with no load. The fuel economy difference was dramatic.
Keep your car in tune. People glaze over when you tell them about the importance of tire pressure, but it’s critical, too (a 3.3 percent economy gain is possibly with proper inflation). Brandon Sturges, a Michelin product category manager, suggests checking out your tire pressure every time you go on a long trip. This used to require you buy an inexpensive item called a “tire gauge,” that some Americans probably don’t know how to use these days (it’s not hard). But fortunately, as Sturges points out, many modern cars make it easy for you by making tire pressure a menu item on the in-car computer. You will get a readout of the pressure on all four tires, though you may have to check with the tire maker (or the owner’s manual, if the original equipment rubber is still on there) to see what the numbers should be. There's more: a badly tuned engine can cost you four percent in fuel economy. If you’re driving around with the check engine light on, indicating a bad oxygen sensor, the impact can be as high as 40 percent, says Fueleconomy.gov.
Combine trips. It’s just common sense. I wish I had all the money I wasted taking books back to the library, when I was going past there the next day anyway. But luckily I avoided a 10-cent fine!
Buy a more fuel-efficient car. As a country we’re going in the opposite direction—even as gas prices are climbing again, and recently topped $50 a barrel. It’s absurd to be driving a sub-20-mpg car in 2016, but that’s what you get when your seven-passenger, off-road-capable Trailbuster has a roof rack on it.
Here are no less than 40 fuel-saving tips, on video: