Hypermiling: Improve Your Car’s Gas Mileage and Save $ on Gas

Readers, are you looking for a few simple ways to save money on gas? This post shares ideas on how to "hypermile" with your car.
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What is hypermiling? It's simply a collection of techniques to optimize and maximize your car's fuel efficiency. If you can build a habit of using even just a few of the fundamental hypermiling tips shared in this post, you could easily save 10%--and perhaps as much as 30%--on gasoline.

Two caveats: this is by no means an exhaustive list of hypermiling tips, and at least one of the tips below could be dangerous if used inappropriately. As always, please feel free to share your own favorite hypermiling techniques in the comments.

1) Know your car's optimal highway speed
In your car's owner's manual you can find your car's optimal fuel efficiency speed. This speed depends on your car's transmission, gearing ratios and aerodynamic profile, but for most automobiles, it's going to be in the neighborhood of 50-55 mph. Whenever you can do so safely, try to drive at this speed on the highway.

Note that in the current era of 65, 70 and even 75 mph speed limits here in the USA, this presents a problem: your driving speed must be reasonable relative to other cars on the road. If your car's optimal efficiency speed is 55 miles per hour, yet you're in a 70 mph zone (which really means everyone's driving 75-80), you risk getting mowed down just to save a few bucks on gas. Find a safe midpoint here and drive with the general flow of traffic.

2) Acceleration techniques
We all have an inner teenager inside us, dying to get a jump on green lights and race ahead of everyone else. I do this too, more than I ought to admit. However, rapid acceleration is just a fast way to waste fuel. It's far more mileage-friendly to accelerate gently and gradually from a standing start.

Your acceleration techniques on the open highway will affect your fuel efficiency too. For example, if accelerating from, say, 60 mph to 70 mph, resist the urge to floor it. Restrain that inner teenager! Remember: you're not impressing the ladies, you're just wasting gas.

3) Braking/Coasting Techniques
Your car uses gasoline to produce forward kinetic energy, which means any time you brake you waste gas. Coasting, on the other hand, conserves that kinetic energy. Therefore, your braking and coasting techniques have a significant impact your car's fuel efficiency.

You can use a wide range of coasting techniques to optimize forward movement with little to no gas. A few ideas:

* Use road terrain to your advantage. Many major highways have hills that are steep, gradual and long enough that you can put your car in neutral and coast for miles at or close to your desired speed.

* Don't approach a long downhill at higher than your desired speed because you'll end up braking the entire way down, wasting fuel, forward momentum--and your brakepads.

* Finally, if you have a habit of racing up to a red light and then hitting the brakes, you're doing it wrong.

4) Vents, not windows
When I was a kid growing up in the 1970s, our family car had "60-WRD Air Conditioning": drive 60 with the windows rolled down. If we'd only known the truth: it's more fuel-efficient to roll up your windows and use your car's interior vents instead. Driving with the windows down is fun and all, but it increases your car's wind resistance and drag. Note that at low speeds or in local driving, this tip won't make a noticeable difference in your mileage--the effect is far more meaningful at highway speeds.

5) High speeds = exponentially more waste
As any math geek will tell you, your car's air resistance (or drag) is a function of your driving velocity squared. In actual English, this means as your driving speed increases, you waste more and more of your fuel on wind resistance. At high speeds, your car burns fuel--a lot of fuel--just pushing air out of the way.

I'll throw some numbers at you: you can generally assume that driving at 70 mph is about 15% less efficient than driving at 60 mph. And driving at 85 mph is about 25% less efficient. Speed not only kills, it wastes money too.

6) Eliminate bad mileage habits
We've already covered a few important mileage-murdering habits like rapid acceleration, driving at high speeds, and so on. But there are several others. For example: do you let your car idle for long periods? Do you overuse your car's air conditioning when using the vents would be good enough? During highway driving, do you repeatedly accelerate and decelerate rather than driving at a steady speed?

Don't worry, no one's saying you can't use the A/C: only the hardest of hard-core hypermilers are willing to swelter in a hot car to save a few bucks on gas. But I will say this: if you do have the habit of repeatedly accelerating and decelerating on the highway you're not just wasting fuel. You should also know the internet has created a rather unflattering term for you. :)

7) Keep your car in good repair
This is the easiest tip of all to follow. Check your oil levels periodically, change your oil when required, keep your wheels properly aligned, and keep your tires balanced and properly inflated. These are basic auto maintenance steps that will help improve your car's fuel efficiency.

8) Avoid ethanol
We've written here at CK about the deeply irresponsible policy behind ethanol fuel mandates. Let's set aside for now the depressing truth that producing ethanol wastes more fossil fuels than it replaces. The real problem hypermilers have with ethanol is this: ethanol burns so poorly that it makes your car less fuel efficient. In fact, at ethanol/gasoline proportions above 10%, ethanol can even disrupt proper functioning of your engine.

The EPA claims that at 10% concentrations, ethanol will cause your vehicle to lose about 3% in fuel efficiency. However, many drivers have found far more significant efficiency losses with ethanol-blended fuels. Bottom line: if you want to improve your gas mileage, keep ethanol out of your car.

Sadly, however, many states mandate that gas stations sell 10% ethanol blend. Our politicians may not understand the laws of thermodynamics, but we--as environmentally concerned drivers--can try to avoid these fuels as much as we possibly can.

9) Drafting
Here's the one fuel efficiency tactic I'm hesitant to share. Why? Because it can be dangerous if misused. But I'll offer it anyway, with caveats, simply because it's the single most powerful hypermiling technique.

Depending on where you get your facts (and depending on your driving speed) wind resistance can reduce your car's fuel efficiency by up to 50%. If you ever look up and see a flock of geese flying in formation, or if you've ever seen riders at the Tour de France draft off of each other, you can see how enormously helpful it is to have someone else take the brunt of the wind for you.

In the context of hypermiling, then, drafting is essentially following a larger vehicle at a safe but fairly close distance, and using that vehicle as a wind break. A typical example is to follow a semi truck that happens to be traveling at your desired speed.

If you follow a large truck at a moderate distance (say, at a 2-3 second following distance) you'll feel a surprising amount of turbulence as your car passes through the same air the truck passed through moments before. Note however, that if you creep up closer to this truck, the turbulence drops significantly--to the point where you can actually start to feel your car being pulled along in the truck's vacuum. All of a sudden you don't need to use as much pressure on the gas pedal to maintain speed.

This is the drafting sweet spot: not so close to the truck that you risk rear-ending it, not so far back that you're sitting in the truck’s worst turbulence. Here's where you can dramatically increase your car's fuel efficiency.

Once again, I offer this specific tip hesitantly and with disclaimers. To return to the Tour de France example, always keep in mind that when the lead guy suddenly stops, all forty of the other guys in the peloton crash right into him. And that's the problem with drafting: it's riskier--and probably not worth it just to save a few bucks on gas. However, if you choose to do it, make sure you stay alert, drive safely and maintain proper following distance at all times.

10) How to manage heavy traffic
The amount of fuel wasted in traffic jams is enormous and probably unmeasurable. As with idling, if your car is running and you're not moving, your gas mileage will be… a big fat 0 mpg. Thus it makes sense as much as possible to avoid traveling during rush hour--and to especially avoid rush hour in major urban centers known for bad traffic.

Sadly, there's no foolproof way to always avoid traffic, so if you are stuck in a jam, you can use certain anticipatory acceleration and braking techniques to limit the gas mileage damage. For example: don't accelerate rapidly to catch up with the car in front of you and then hit the brakes as you approach. Instead, accelerate gently and then coast. Further, keep your eyes on what's happening several cars ahead of you, and try to anticipate and match the general movement of traffic with as little braking as possible. If you see nothing but brake lights a quarter mile ahead of you, there's even less reason to race up to the bumper of the car ahead of you.

Wait a second: does all this hypermiling stuff really work?
Yes, it actually works. Readers, about a year ago, on a long road trip from New Jersey to Texas, I did a control test: I drove normally for one full tank of gas, and drove a separate full tank's worth of gas using as many hypermiling techniques as I could from the list above.

I'll admit up front: I was cynical about the value of these hypermiling techniques. I didn't think I'd see that big a difference. And yet the improvement I was able to get in gas mileage was substantial--far greater than I expected. Normally, my car (a 2009 Pontiac Vibe) gets about 30-32 miles per gallon in highway driving. Using hypermiling techniques, however, I was able to get my fuel efficiency up to nearly 40 miles per gallon. That's a 25-30% improvement, and it translates directly into a 25-30% savings on gasoline costs.

Yes, this was just one trial, and yes, it was neither exact nor scientific, and yes, your mileage may vary (heh), but I encourage you to try some of these techniques yourself and see if you can see a difference. I'm guessing you will.

One final thought. Individually, many of these tips won’t have much of a noticeable impact on your gas mileage. But use a few--or all--of them and collectively they’ll be significant. It’s not that difficult, for example, to draft off the occasional truck here and there, build better acceleration and braking habits, and drive at a consistent and moderate speed. Just doing these things could improve your mileage by 10-20% with minimal effort. Try it--and reap the savings!

Readers, what do you think? What’s your favorite fuel saving technique?


For Further Reading:
1) MPG for Speed: a simple one-page site that walks though some of the mileage/fuel efficiency losses your car experiences at higher speeds.

2) What increased speed and air resistance does to your car’s fuel efficiency.

3) For the serious math geek: an article that looks at a several different ways to calculate energy loss at high driving speeds.

4) Top Ten Ways To Waste Gas.

5) How Does Ethanol Impact Fuel Efficiency?

6) Interesting and somewhat technical discussion thread on ethanol and fuel efficiency at the Eng-Tips Forum.


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