Want better gas mileage? Stop driving like you know what
CLEVELAND, Ohio – Your erratic driving isn’t just annoying the people in your passenger seats. It could also hurt your wallet and get you fewer miles per gallon.
how? Well, the science involved is largely to blame. Going faster than the speed limit or constantly stopping and accelerating uses more energy than traveling at a constant speed.
I hope that’s not true, because I find this kind of safe driving very boring. But David Cook, senior associate director at Ohio State University’s Center for Automotive Research, said the average driver could save 10% on gasoline by driving more efficiently.
An aggressive driver can reduce their vehicle’s gas mileage by up to 40%, according to the US Environmental Protection Agency.
Here’s some of the science behind it.
Going faster is harder
Why does driving above the speed limit affect fuel economy? The simple answer, Cook said, is that moving faster uses more energy.
It gets a little more complicated than that because of how aerodynamic resistance — known as drag — affects your car.
A car needs enough energy to move its mass, and it must deal with rolling resistance – the friction between the tires and the road.
If your car is going 10 times faster, it needs 100 times more power, Cook said.
How your car handles this depends on a lot of factors, like how the front of your car is shaped (think an open hand sticking out the window versus a closed fist). But tests conducted by the American Automobile Association, known as Triple A or AAA, show just how impactful this can be.
For example, a Toyota Prius got 58 mpg at 60 mph but only 47.5 mpg at 70 mph. The Ford F150 got 24 mpg at 60 mph, but only 19.4 mpg at 70.
On average, vehicles ranging from the Cadillac Escalade to the Ford Fusion Hybrid got about 3 mpg less for every 5 mph faster, according to AAA tests.
Hard braking breaks the bank
There is one big caveat here – vehicles get much better mileage On the highway compared to urban areas, such as cities. But this is less about speed and more about stopping – lots and lots of stopping.
Acceleration – or acceleration – requires much more energy than traveling at a constant speed. Therefore, a vehicle on the highway, assuming the driver is using cruise control and not constantly interrupting people in traffic, can travel at a set speed.
But all that energy stops being useful when there’s a red light in front of you. When the driver presses the brake pedal, the pads press down on the wheels and cause more friction, converting all that energy into heat.
This is obviously a good thing, because it stops the car. But this means losing power, and the driver will start again at zero.
Side note: Electric cars use something called regenerative braking and harness that energy to recharge the battery. However, most readers still use internal combustion vehicles.
This doesn’t mean you should run stop signs to save money. But this means that accelerating more smoothly and slowing down gradually will consume and lose less energy. Which will improve your fuel efficiency.
Vehicles have a cool thing called a transmission, and that kind of makes things more complicated, Cook explained.
Engines have an efficiency curve and use gasoline better at different operating points, Cook said. A car running at 8,000 rpm will not be as efficient as a car running at 2,500 rpm.
But vehicles have different gear ratios, which means automakers can make sure your car’s engine runs well at different speeds.
That’s why you’ll see a 10-speed transmission more commonly than a three-speed, Cook says. Automakers have turned towards Use a transmission with more options as a way to help with fuel economy.
This is why you can’t say that driving 25 mph is always better than 35 mph, Cook says. It all depends on how automakers modify their vehicles.
Manufacturers use something called a chassis dynamometer, a kind of automobile treadmill, to test fuel efficiency. These tests put vehicles into a predetermined route — one for city driving and one for highways — to determine their advertised mpg.
Like anything that is tested, you design around the test, Cook said. The tests will take vehicles at legal speeds that often exceed 80 mph Or 100 mph. It is natural for automakers to make vehicles efficient at these speeds.
How do you say on your car? RPM is a good indicator of fuel economy, Cook said. If your car runs 3,000 rpm at 25 mph and 3,000 rpm at 35 mph, you can be pretty confident that your fuel economy is about the same.
If your engine is revving at a high speed and the RPM dial is shifting too far to the right, your driving is probably not very efficient.
How much can you save?
All of this advice can be a bit confusing, and there’s plenty of other advice online, but the main thing to keep in mind is that hard acceleration, hard stops, excessively fast driving, and constantly changing speeds are generally a no-no.
Cook said a drop from 65 to 61 mph won’t make much of a difference, and it’s of course a bad idea not to follow the flow of traffic. You will see more gains by not stopping and starting so much.
The real question is, how much money could driving better save you?
The EPA says aggressive driving, which it defines as speeding, rapid acceleration and braking, can reduce gas mileage by about 15% to 30% at highway speeds and 10% to 40% in stopped traffic.
Gas mileage tends to decline quickly after vehicles exceed 50 mph, according to the EPA. You can view your vehicle tests at Fueleconomy.gov/feg/driveHabits.jsp.
For example, we’ll look at my car, a 2015 Toyota Camry. If you buy gas at $3 a gallon, driving 60 mph is like paying $3.43, and driving 70 mph is like paying $4.01, according to the EPA.
At just 10 miles of highway each workday, or roughly 2,600 miles a year, that kind of speed would cost me about $60 a year.
How much you’ll save depends, of course, on how you drive now. When I tried it myself, it took me a few minutes to figure out how to use the cruise control system, so I have some work to do.
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