Three MPG myths

It amazes me sometimes what people believe to be true. Even more so how they will cling to those truths, even in the face of clear facts and reasoned arguments. Indeed, when it comes to talking about cars I often find myself shaking my head at the stubborn dogmas that people hold on to.

Nowhere is this more prevalent than in discussions on fuel economy.

With fuel prices and social consciences high, people are looking for any way possible to reduce their own usage of fuel, cut down on our nation’s dependence on oil from other countries, and limit the environmental impact of our cars. These are all both reasonable and noble goals. Unfortunately, many of the steps that are being taken are not really effective ways to reach them.

But don’t tell that to someone who believes he is saving the world.

Nevertheless, I have decided, dear readers, to share with you a few common misconceptions about driving, cars and fuel economy that I have encountered over my years of automotive enthusiasm. You can take my advice or leave it, of course. As long as I have succeeded in getting you thinking, I will be happy.

Pumping up tires will use less gas and save me money. The first part is fundamentally true. A harder tire will offer less rolling resistance and, therefore, you may see an increase in fuel mileage if you pump your tires to the maximum inflation rating. But first consider the trade-offs. On the driver’s front door frame of your car you will likely find a label that includes, among other things, the manufacturer’s recommended inflation pressure for the tires. This is not some number that they pull out of thin air. It is instead a carefully considered value that takes in to account ride comfort, vehicle handling and braking, and tire wear and suspension wear.

Increasing your tire pressure by 10 psi, for instance, will put abnormal pressure on the center of the tread where it contacts the road, causing it to wear very quickly on that part of the tire. Did you save money on gas? Maybe, but now you need new tires way before you otherwise should. I doubt you saved enough to compensate for that.

Overinflating the tires can also cause changes in the way a car handles and brakes. Hard, hyper-inflated tires can be unpredictable in hard cornering and dramatic direction changes, losing grip on the pavement much sooner than a properly inflated tire. Now, I’m sure you’re saying to yourself, “well, I don’t drive aggressively. I can just be careful.”

Yeah, right up until the moment that truck in front of you on the interstate has a blowout and you have to jerk the wheel to avoid the shards of rubber.

I could go on giving examples here, but suffice it to say, yes you can save some gas money by pumping up your tires. But it may cost you a lot more than you think.

I drive a manual transmission car. If I change gears at as low an engine speed as possible, I will save gas. There is some basic physics involved in this, so bear with me. Sir Isaac Newton tells us that an object at rest tends to stay at rest and that an object in motion tends to stay in motion. Think of your engine as an object in motion (on the inside, at least). When you accelerate, the engine spins faster and faster until you change gear and it drops back down and starts the process again. At faster rotations, because the engine is already moving quickly, it takes less fuel to keep it moving quickly. This is obviously a very basic explanation, but the theory is correct. Also, at some point the engine starts to spin too fast to use the fuel efficiently, necessitating a change of gears.

Changing gears very early, though, slows that momentum prematurely and the computer must compensate by adding more fuel to keep the engine spinning and moving you forward. So by changing gears too early, you may actually be using more fuel than if you had simply let the car accelerate the way it was intended.

How do you know where are the optimal places to change gear? Try the owner’s manual. You know, that book that sits in your glove box? There is all sorts of neat stuff in there about how your car is intended to work, including where your transmission is designed to be shifted most efficiently. If your manufacturer hasn’t seen fit to include that piece of information, you can certainly find it online. There are some truly epic nerds out there that spend all kinds of time figuring that stuff out. I’m sure one has your car. Google it!

Anyway, the point is this: drive your car the way it was intended and you may be surprised at the returns you see.

Buying a hybrid means I am doing my part to save the world – and I am getting great fuel mileage at the same time! This is more of a peeve of mine than an actual myth, but hear me out.

Hybrids get good fuel mileage. I don’t dispute that. According to the EPA’s site, for instance, a 2009 Toyota Prius is rated at 48 miles per gallon city and 45 mpg highway. Not bad, for sure.

But where do the batteries come from? As this author points out, many of the ores that find their way into our batteries do so through some very dubious means. And even those that come from less volatile areas of the world like Canada are extracted through mining processes that are damaging.

Once the ores have been mined and the materials gathered they have to be transported to some central location to be manufactured into their various parts, which are then transported again to where the vehicle is assembled. The entire process, as Top Gear’s Jeremy Clarkson loves to point out, is more damaging to the environment than driving a V8 SUV.

And, frankly, I don’t think the gas mileage numbers are even all that good. A Toyota Yaris of 2009 vintage will return 36 mpg on the highway and uses a single old-fashioned lead-acid battery. A Honda Fit will return 35 mpg and the new Mazda2 will do much of the same.

Hell, I have gotten 40 mpg from my CRX and, when I still had it, 44 mpg from my old ’93 Civic CX. None of them have large, heavy battery packs made of ore mined in violently conflicted regions.

The point is, there are many ways to get excellent fuel mileage. Hybrids are one of them. They are not, however, all butterflies and rainbows.

So there it is. All of these are simple, common sense things that, if given the opportunity, a reasonable person would be able to see for the myths that they are. So what, if you want to actually get better mileage and make a difference, should you do? Well, that’s an article for another time.

About Chris Nelson

Chris is a writer and communicator with backgrounds in public relations, communication, political science and automotive technology. He holds an M.A. from Rowan University and a B.A. from Susquehanna University in addition to a certificate in Auto Tech from Lincoln Technical Institute.

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