Musings
Hypermiling
Hypermiling
Hypermiling, as defined by wikipedia, is the act of driving to exceed the EPA estimated mileage on your vehicle by modifying your driving habits. That definition is quite loose and a handful of folks out there have taken hypermiling to an extreme. Just enter "hypermiling" into any search engine and you will come across some examples of what I am referring to. My experience with hypermiling is a bit more practical.
It all stemmed from Mike's all time favorite TV show, Top Gear, the British authority on everything automotive. A story on one of the episodes was a challenge of whether or not one of the stars, Jeremy Clarkson, could make the drive from London, England to Edinburgh, Scotland, and back, on just one tank of fuel. The round trip distance for the trip is 800 miles. The car he drove is the Audi A8 with a turbocharged V8 engine. We are all aware that a V8 engine is far from economical, so Mr. Clarkson had to employ some crafty tricks to extend every last mile out of that tank of fuel. To succeed he would need to average 40 mpg. The piece is very well done and nicely dramatized, and whether or not you can believe it, he DOES make it there and back on a single tank of fuel.
Watching this segment taught me a lot about extending the fuel economy for a tank of gasoline. I started employing the tricks here and there and saw results. One by one, I began assimilating the driving tactics into my typical driving habits. The results are remarkable, and for me, well worth continuing. I intend to share with you the habits I have acquired that have made a significant difference. Take 'em or leave 'em, but I promise, if done correctly, you WILL see results!
I drive a 2 wheel drive 2003 Pontiac Vibe with manual transmission. A lot of the following tips mostly apply for manual transmission; however, if you drive an automatic transmission, don't stop reading. Many other tips can still apply to you, too.
- Remove excess weight from your trunk/hatch and backseats
Even though the case of water you have been hauling around in your trunk since you visited Costco last week may seem negligible compared to the gross weight of your car, get rid of it! For one thing, if you get in an accident, the last thing you want are random projectiles flying around the interior of your car. Also, the more mass that has to get moving from a stop requires more energy (i.e. fuel) to accelerate. You remember Newton's 2nd law, right? F=ma! The idea is to keep m (mass) only as large as necessary. - Drive with windows up
If you can help it, keep those windows up. Windows that are down increase your car's drag, making it less sleek and slippery. The drag is a force that acts to decelerate your car, requiring more energy (i.e. fuel) to overcome it. - Do not use AC
If you live in a fairly temperate climate, avoid using the air conditioner. Like many of the electrical components (and conveniences) of your car, the AC requires an energy source. That source is the engine (and the fuel burning in it). The less draw the AC requires, the more fuel that can be dedicated to a tank's mileage performance. Using your AC can reduce your miles per gallon performance by 15-25%, depending on the vehicle (ref). - Only listen to the radio
One of those conveniences that draws a fair bit of current is your sound system. The CD player and/or tape deck (*gasp*, do people still have these?) draws enough current to be noticeable against your mileage performance. But don't despair, if you do most of your driving in populated areas with a decent radio station selection, feel free to get your driving entertainment from the radio. The radio draws so little current that it is negligible against your fuel consumption. Note, however, that an after market sound system will negatively impact the mileage you get on a tank. Those big speakers are driven by one or more amplifiers. So, keeping the volume low will draw less power and save mileage. - Drive the speed limit
Keep your speed down. Keeping your speed at the limit will greatly stretch your tank's mileage performance. Of course, make sure you are in an ideal gear for the speed so that you can keep your engine's RPMs down. For those driving manual transmission, you have an added advantage. For slower speeds, you can choose to put your engine into a higher gear to even further reduce the RPMs. For the way my Vibe's transmission is geared, I generally shift by 2000 RPMs and like to keep it below that number for all city driving. On the expressway, I keep my RPMs at, or below, 3000.
For you folks out there that appreciate the language of math, the drag equation looks like this:
An additional benefit to driving the speed limit, is you no longer have to be on the look out for law enforcement. That stress is entirely removed. That alone has been one of the greatest rewards in acquiring my new driving habits. - Acceleration
This is where most drivers will get awful miles per gallon performance. Most drivers punch the gas hard to get moving quickly. To see better mileage results, accelerate slowly and evenly. Shift early to keep the engine's RPMs down. You will not be beating anyone off the line, but you can smile knowing you are spending less money! - Deceleration
Just as you should accelerate slowly, you should decelerate slowly. Braking KILLS your gas mileage. Remember Newton's first law? Objects at rest tend to stay at rest and objects in motion tend to stay in motion, unless acted upon by an outside force. In this case, the force is your brakes. Braking does not act to conserve your car's momentum. Regaining that momentum will require energy (i.e. fuel). Now, this is not to say you should never brake. I am not condoning unsafe driving. But what I am saying is to judge your braking. Flying up to a stop light/sign in order to break hard at the last minute is not doing your mileage any favors (or your brakes, for that matter). When a light turns red, let off the gas and let your car coast. Be sure to leave your car in gear, and down shift as the car decelerates. Not only will you gain the benefit of some "braking" by the engine, but coasting in gear requires NO fuel. The engine's RPMs are governed by your wheels rotating and driving the engine. As soon as the wheels stop turning, the engine will shut off unless you apply gas or take the engine out of gear. You can choose to coast to a stop with your engine in neutral, but know that it takes some fuel to keep your engine at idle. Coasting in gear is free! As a side note, some might argue that downshifting will increase wear on the clutch. Either way, the clutch will last a lot longer when not abused, like with full throttle starts!
Another benefit for decelerating slowly (i.e. over a longer distance) is that by the time you near the red light, it may have already turned green and you will never have had to come to a complete stop. It requires much less energy to accelerate a car that is moving than a car that is completely stopped. - Do not tailgate
Whenever you are driving on a congested stretch of highway you probably notice that everyone is packed in, bumper to bumper. Leaving plenty of space between you and the car in front of you is a no brainer. Keeping that braking/deceleration tip in mind, allows room for you to slow down when you see their brake lights light up. Instead you tapping your brakes as soon as they do, you just let off the gas and slowly close the gap. By the time the gap is closed, the person has already accelerated, so you never have to stop, thereby conserving momentum much better than those around you. You may notice truckers doing this all the time. Those rigs have so much inertia to overcome, the last thing they want to do is come to a dead stop.
As an aside, leaving plenty of room between you and the car in front of you also alleviates one of the main problems that often leads to traffic jams -- merging. During rush hour or construction, there are more cars on the road than the road was designed to handle. Merging slows everything down because no one wants to let the other guy in. But by creating that space between you and the car in front of you, the new car can merge seamlessly with no braking required. Everyone wins! - Hills
Driving hills is where most drivers really lose out on mileage performance. The idea behind hills is to conserve momentum and use gravity to your advantage. There are several ways to drive hills economically. The idea is to gradually build up speed as you approach the base of the hill. As the car ascends, keep the acceleration very steady and slightly reduce the gas to the engine. The way I time it is to reach the top of the hill slightly slower than I was driving at the base. If there is no one behind me, I may let off the gas completely and rely on the car's momentum to reach the top -- a free ride! On the descent, there are two camps of thought. Some accelerate on the descent, using gravity to supplement the speed that the fuel supplies. This works well for rolling/continuous hills, allowing your downhill speed to be your momentum on the ups. For a hill with flats just beyond it, I tend to keep the car in gear, let off the gas, and coast. If the hill is steep enough, the braking of the engine will keep you within a reasonable speed, and again, its a free ride all the way down! - Idling
For the moments your car is idling you are getting 0 mpg. Ouch! Try to avoid sitting idle as much as possible. Sitting in your friends driveway waiting for them to get ready? Turn off your car. Turn you car on 15 minutes before you head to work on those brutally cold mornings to get it "warmed up"? Don't do it. Your engine will warm up faster when you are driving it, when RPMs are higher than idle. Your heater will respond quicker and you will be comfy before long. Sure, you will be cold for a few minutes, but at least you have piece of mind knowing you are getting better than 0 mpg! In some countries, folks turn off their engine when they are stopped at a red light. The amount of fuel it takes to start an engine is equivalent to 3 seconds of idling. That is not much.
Those tips being said, driving requires a lot of concentration -- more than you may have ever put toward the task. If you adopt these habits, though, before long they will be second nature. I cannot promise you will be loved on the road, however. I get sneers and watch frustrated drivers race past me. Use these tips mindfully and try not to pose a hindrance to the general flow of traffic.