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Hypermiling: EPA estimates vs. your car
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Hypermiling is a practice rich with techniques and tips, and presents opportunities for fuel economy savings from the moderate to the very significant. Many who have heard the term and understand the concept unfortunately take it to be all about hybrid automobiles. While hybrid owners certainly factor in the hypermiling community, anybody who drives a car can benefit from the practices of hypermiling.
EPA mileage estimates vs. your car
Anyone who has ever purchased a new car or even been to a new car dealer over the past 30 years or so, has seen the big, bold numbers affixed to one of the side windows stating that particular automobile's estimated city and highway mileage rates. The Environmental Protection Agency (EPA) developed standardized testing to determine a given vehicle's average mileage performance in both stop-and-go driving, and in driving on the open road. Auto manufacturers test their own vehicles. At best, the EPA's test standard prior to 2008 was flawed, and the results generally reflected higher numbers than the average driver can get from a vehicle. In 2008 the EPA revised its testing to more realistic models, and most mileage estimates are now lower. (Get a detailed explanation of EPA testing: http://www.cleanmpg.com/forums/showthread.php?t=1510 Section I- History and Methods of the EPA's Fuel Economy Estimates)
But what is "mileage?" Expressed in the rate of "miles per gallon" (MPG), it's quite simply that: how many miles a particular car travels on a gallon of fuel. This is where creating a mileage log, mentioned in earlier articles, becomes important. In addition to simply telling you how far your car went on a tankful of fuel (see www.examiner.com/x-15291-Chicago-Hypermiling-Examiner~y2009m6d26-Hypermiling-from-the-start), your trip odometer reading can also be used to calculate your mileage. Once you've filled up your tank, take the trip odometer reading and divide that number by the number of gallons of gas it took to fill up the tank this time.
A recent example from my own log book: 314 miles/17.188 gallons of gas=18.27 miles per gallon.
Comparing that to my 2002 Nissan Xterra's EPA estimate shows, with that tank of gas, I beat Nissan's estimated 17 mpg combined estimate, based on their testing, as well as the lower estimate based on the EPA's revised standard.
To find your vehicle's EPA estimates, go to http://www.fueleconomy.gov/feg/findacar.htm and click your way to your specific brand and model of car. The results page will show you what the estimate was when your car was new, and the equivalent estimate based on the new EPA testing standard. Then you can begin comparing your mileage with each tank of gas to track your mileage improvements.
Coasting
Another of the simplest techniques of hypermiling is coasting. It does not mean simply taking your foot off the accelerator pedal!
You have applied the gentle acceleration technique and now your vehicle is up to speed. Our tendency as drivers, when we crest a hill or we approach a traffic light, is to simply take our foot off of the accelerator pedal until it's time to depress the brake pedal. During the time between releasing the accelerator and pressing the brake, the engine is doing what is called compression braking. We're not pushing it to go faster, and we're not asking it to maintain a speed, so it's trying to return to its idle speed, and slows the vehicle. At the same time, the car's inertia is keeping the engine turning faster than what we're demanding, because everything is all tied together: wheels, drive train, transmission, engine. As the engine works against the car's inertia, turning at the car's speed, the car's fuel pump is still sending gas to it at the demand of the car's speed, and that gas is being burned just to slow down the car! It's a little different in a car with an automatic transmission than it is with a manual transmission (the automatic transmission allows the engine to run more slowly in deceleration), but the effect is essentially the same.
To save fuel by coasting is very simple. When you're heading down a hill or you're approaching a traffic light, gently slip the transmission selector lever to the 'N' position. This will disengage the transmission from the power of your engine, and you're coasting. Your engine will slow to its idle speed. Heading down the hill, you can control your speed with the brakes. At the bottom of the hill you can return the lever to the 'D' position and use the accelerator as normal.
When you reach the traffic light or the traffic stopped there, keep your car's transmission in neutral until you're ready to move again. With the transmission in gear and your foot on the brake to keep the car motionless, the engine is under a load and is using more fuel.
With a manual transmission, simply depress the clutch pedal in order to coast, and use the brakes to control your speed. Before shifting back into gear, you may wish to rev your engine enough to match the RPM to the vehicle's speed. As you gain more experience with coasting, this becomes easier, and is then easier to form into habit.
The flat-to-gently-rolling terrain of the Chicago area and northern Illinois is especially conducive to coasting. Pay extra attention to the road ahead of you; on level ground in open country, if you see a traffic light (or other potential obstacle) half a mile or more down the road, you can shift to neutral and coast the whole distance to the traffic light. It may not seem like much, but over a long trip, or over a month of driving daily over the same route, that can mean several miles of travel that your engine didn't have to work for.
City driving is usually stop-and-go, which is normally a mileage killer. However, applying the same techniques will save some gas. From one traffic light to the next, accelerate easily and smoothly. Once up to the limit, or the speed of the flow around you, shift to neutral and coast to the next stop, or until you need to keep to speed. There's no reason to rush to the next red light!
As always, let safety and common sense dictate. If you drive in an extremely hilly area it may not be safe to rely on the brakes alone to slow a descent. In heavy city traffic, it may sometimes be necessary to drive more aggressively. If you're uncomfortable with any hypermiling technique, or you're not used to implementing them in stressful situations, it is better to revert to "normal" driving. Your safety is always worth more than any fuel savings.
If there is a lot of driving ahead of you this holiday weekend, it may be a good time to start hypermiling. Using only the techniques detailed thus far in this column can noticeably increase your gas mileage and start saving you some money. Enjoy the weekend, and please drive safely.
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