Reason for a New Age

Driving to Save Gas

Posted by publius2point0 on 2011/02/06


In the forthcoming years, cars will continue to be given higher and higher levels of MPGs as they go on sale. This will be accomplished through various means of mechanical trickery which improve efficiency and reduce the amount of power needed in the first place (like better aerodynamics).

However, it’s worth noting that one can achieve differences in fuel consumption in the realm of the double digits (like 20-30% less fuel use) just by changing the way that you drive. Obviously, that will depend on your driving habits as they are now.

The big rules are effectively:

  1. Don’t speed up
  2. Don’t slow down
  3. Slower is better

Don’t Speed Up

As you may recall from grade school, Newton had several laws about motion. The first of these laws was, “Every body remains in a state of rest or uniform motion (constant velocity) unless it is acted upon by an external unbalanced force. This means that in the absence of a non-zero net force, the center of mass of a body either remains at rest, or moves at a constant speed in a straight line.” That is to say, everything has “inertia”. To maintain a vehicle at a particular speed requires very little energy as the car’s inertia wants the car to continue to move at that same speed. But when you are accelerating, you are fighting inertia, and spending extra fuel to do it. Fighting it more strongly — for instance, trying to accelerate a lot all at once — eats even more.

If you must speed up, then you might also consider waiting until you are on a downhill slope. This way, you already have a force on your side helping you to accelerate. On the other hand, you never want to accelerate when you are going uphill, as then you are fighting both inertia and gravity together. You might even consider letting the car decelerate as it goes uphill, rather than applying more gas to maintain speed. Once you’re flat again, it will be easy enough to get back up to speed.

Don’t Slow Down

It cost you fuel to get up to the speed at which you are traveling. When you apply the brakes, every bit of fuel that you spent accelerating to your current speed is, effectively, lost. You are wasting all of that energy by turning it into waste heat at your brake pads.

Obviously, at some point you must slow down. But quite often you know ahead of time that you are going to have to stop. For instance, if you look ahead and see a distant stoplight turn red, then why keep your foot on the gas while you approach? If you simply let the car coast in neutral, you’ll still get to the light, so why waste the gas on maintaining speed up to that point? And of course as the car decelerates on its own, without the use of brakes, it takes longer to get to the light. By the time you begin to approach, the light may turn back green and you can proceed on. If you had gotten there sooner, you would have braked fully, losing all inertia, whereas now you only lost some.

Slower is Better

Air is, actually, a solid. If I stick a boat with a large sheet of cloth on a lake, it will be pushed quite forcefully along.

We generally don’t notice this solidity because we are moving quite slow. Just the same as I don’t notice how resistant water is when I swim gently, when I leap off a bridge into a body of water, it suddenly seems quite solid.

The faster you move through a material like air or water, the more resistance there is to just maintaining that speed. While inertia does make it comparatively easy to maintain speed, for every little bit faster that you are going, the amount of fuel necessary to maintain that speed increases.

Getting back to the example where we see a light change to red ahead, it’s also worth noting that quite often you’ll get a green light just as the next stop light turns red. Obviously you will need to accelerate some just to get to the next light, but why not accelerate to no higher speed than necessary for the light to change again before you get there? The people behind you will wonder what you are up to, but really that’s their problem; you’re saving fuel.

If the speed limit is 60, while yes that does mean that you can go something more like 62 without needing to fear any policeman, you can also go something more like 58 and still not worry.

Other

Of course, there are other things you can do to improve your fuel efficiency — and I’ll provide some links at the end so that you can see them — but one thing you might not usually think of is to cast off excess weight.

You see, while our fuel efficient cars of today are reaching something like 45 mpg (in the case of the Toyota Prius), back in the late 70s and early 80s, we had regular gas guzzling cars without any odd modifications achieving miles per gallon in the realm of 60-65. The difference was that these were small and light cars, whereas the cars from the 80s on had to pack on hundreds of extra pounds to meet the safety standards of modern day. As an example, the classic Mini Cooper weighed about 1500 lbs. The new one weighs about 2500. The original VW Beetle was about 2000 lbs, the new one is 2700. Accelerating a greater mass takes a larger amount of energy, and hence more fuel.

If you want to save money, depending on the lengths to which you are willing to go, you could cut a fair significant amount of fuel use by lopping bits off of your vehicle. Take the plastic cover off of your engine. Take the rugs and carpeting out. Have the big, heavy seats replaced with minimalist racing seats. This doesn’t even need to be permanent, you can set these items in your garage and have them put back in when you sell the car. The cost of doing this work will almost certainly be cheaper than a new car, and just as likely you’ll earn the cost back in fuel savings before long.

It really just depends on how much you care and to what lengths you are willing to go.

Personally, I drive 62 mph and couldn’t be bothered to strip my car. But I do let the car coast to a stop and don’t accelerate towards a red light. But that’s me.

http://www.fueleconomy.gov/feg/driveHabits.shtml
http://cars.about.com/od/helpforcarbuyers/tp/ag_top_fuelsave.htm

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