100+ hypermiling / ecodriving tips & tactics

[JohnnyGrey]

As for the untrue ones. Driving with your lights on does not decrease your fuel
efficiency. On any vehicle the alternator is turning at the same relative speed as
the vehicle's engine.

This doesn't make one bit of difference. The more amps you draw, the more torque and therefore power, the alternator will demand.

[basjoos]

Here's some injector pulse widths from my SuperMID with various combinations of accessory electrical loads turned on. It was made after returning home from a 25 mile trip so the engine was completely warmed up. The SuperMID shows the change in pulse width within seconds of turning on the electrical load. Below are the results.

Warm idle with nothing turned on........2.3 to 2.4
Parking lights on..............................2.4
parking and headlights on..................2.6 (high and low beam are the same)
Brakelights on.................................2.4
Fan on lowest speed (level 1)............2.4
Fan on next higher speed (level 2)......2.4
Fan on level 3.................................2.4 to 2.5
Fan at max speed (level 4)................2.5
A/C and fan at level 2......................3.6
A/C and fan at level 4......................3.7
radiator fan on................................2.4
Radio on with volume fairly low...........2.3

I also monitored the pulse width for the 1st minute of idle when starting a cold engine at 55F ambient temp.
Start idle.........4.2
After 30 sec.....2.9
After 1 min.......2.6

When restarting a warm engine with the starter, the pulse width returns to normal within about 5 seconds, when bump starting, the pulse width is back to normal within a second.

From past observations, turning on the headlights drops my mileage by about 2mpg.

[cloudjunkie]

I just want to point out that the aerodynamic drag on a moving body increases quadratically (i.e., to the second power like V^2) with velocity and not exponentially (i.e., e^V). This distinction is very important.

I also want to comment on the issue of the effect of headlights on MPG. At a speed of 55 MPH, the engine of a normal sedan needs to provide on the order of 10 HP to achieve a constant speed. Now, 10 HP is equivalent to about 7.6 kW (that's kilowatts) of power to overcome aerodynamic, road, and mechanical resistance. Now, my headlight bulbs say they use 100 W of power each, so having both headlights on requires about 200 W of power. So the proportion of energy the headlights use compared to the energy required to keep the car moving is

200/7600 = 2.6%

Thus, the engine will use roughly 3% more power to supply the energy to turn the alternator and power the headlights (energy must be conserved, the source of energy for the alternator is supplied by the belt that the engine is turning). If a car gets 30 MPG at 55 MPH, it wouldn't be unreasonable to expect a maximum decrease on the order of 1 MPG by having the headlights on. I spend roughly about 20% of my driving distance with me headlights on; thus, I would expect roughly a 0.2 MPG decrease in total gas mileage. That's pretty small, and I would have to question whether driving without headlights is worth the trade-off in safety.

Of course, your MPG after a head-on collision is technically infinite, unless your car is on fire in which case you get 0 MPG, but at that point you might not be worried about your MPG.

Lastly, the accord of basjoos gets about 60 MPG, so his observation of experiencing a 2 MPG decrease in gas mileage with headlights on is consistent with the rough calculation performed here.

[SVOboy]

I don't think anybody is suggesting driving around in the dark with no lights on...

[cloudjunkie]

Originally Posted by SVOboy

I don't think anybody is suggesting driving around in the dark with no lights on...

No, but how about the temptation for someone driving through a safety corridor in the middle of the day to keep their lights off thinking they are somehow saving a bunch of gas? They're not saving much fuel, that's my point.

I certainly have a stake in arguing against keeping your headlights off in such situations: I drive in them regularly and would like vehicles to be reasonably visible.

[SVOboy]

I have never driven in a safety corridor, so I don't really know what they are, but I wouldn't tell someone to turn their lights off somewhere it was unsafe or unlawful (assuming the law has purpose)...

Nevertheless, I don't think that the problem of people making unsafe decisions should be cause to suppress information. 3% is all I've ever seen for headlights, and I don't think anyone tries to misrepresent that.

I firmly believe that the best choices will be made with the most information, is all,

Welcome to ecomodder, by the way, it's always nice to have thoughtful, analytical people like yourself on board,

[jamesqf]

An interesting list of tips. I'd like to suggest a few more that I've found useful.

A) Take a bit off the tops of hills. Most roads are cambered, and curves are banked, so one side of the travel lane will be lower than the other. Take a line to that side. (This will often shorten the distance travelled, as well.) The same applies in reverse on the dips...

B) Drive on the smoothest part of the road. Often this is not the center of the lane, where most cars travel (as you can see by the wear pattern). If your car's narrower than the average, you can often drive with one side near the 'hump', putting all the tires on smoother pavement. (This only applies on dry pavement, of course.)

C) In cold weather, block off part of the radiator so the engine warms up faster, and stays warmer on downhills. This is best done if you have a ScanGauge or similar reader that will give you precise coolant temperatures. OEM gauges don't seem to be accurate or even linear.

[cloudjunkie]

Originally Posted by SVOboy

I have never driven in a safety corridor, so I don't really know what they are, but I wouldn't tell someone to turn their lights off somewhere it was unsafe or unlawful (assuming the law has purpose)...

Nevertheless, I don't think that the problem of people making unsafe decisions should be cause to suppress information. 3% is all I've ever seen for headlights, and I don't think anyone tries to misrepresent that.

I firmly believe that the best choices will be made with the most information, is all,

Welcome to ecomodder, by the way, it's always nice to have thoughtful, analytical people like yourself on board,

I definitely think the discussion in this forum is great and certainly also think that information is good. I certainly just wanted to encourage people to also make safe choices in their driving habits. There are certainly situations when driving during the day without your headlights on would be perfectly fine and would indeed save some fuel, albeit a fairly small amount which to a true ecomodder would be worth it.

I mainly wanted to provide some justification that having your headlights on will decrease your fuel mileage, and by what amount you could reasonably expect. There was a question on Car Talk some weeks ago about this question, and I thought that it should be possible to arrive at an answer with a simple calculation.

I think this is a great site with good discussion!

[cloudjunkie]

Originally Posted by JohnnyGrey

This doesn't make one bit of difference. The more amps you draw, the more torque and therefore power, the alternator will demand.

I agree!

Some more insight can be gained by a simple thought experiment. Suppose that instead of the alternator powering headlights, it was powering an electric motor. Now suppose that electric motor replaced the engine and as such was powering the alternator. If the alternator indeed did not take energy from the motor, as would be the case if the alternator did not take anymore energy from the engine if the headlights were on, then the electric motor and alternator should then be able to run indefinitely without outside energy. This is the basis for a perpetual motion machine, which violates the conservation of energy law of physics. What we can learn from this is that when the headlights are on, the alternator must draw energy from the engine to supply the headlights with power so that energy is conserved.

The amount of energy is small, perhaps only reducing your gas mileage by 3% (see my calculation on this thread and the experiences of several in this forum), so it would be difficult to detect except with careful measurement.

[Tango Charlie]

Great list!
How about this one;
Imagine an egg between the accelerator and your (bare) foot. Helps prevent jackrabbit starts.
And maybe I missed this one on the list, but;
Never Downshift