Fun With Hypermiling - Part 5

Part 1 - Introduction - "What is Hypermiling?"
Part 2 - Test Hypotheses
Part 3 - Fun with air filters
Part 4 - We're talking tires
Part 5 - Driving techniques

In Part 4, we talked about the trade-offs between adjusting tire pressures and gaining fuel mileage. By doing this, we gained 1.5mpg, for an average annual savings of 858 miles of fuel saved equalling 23.8 gallons per year which, at $3.44 per gallon, is an annual savings of $81.87.

The next step was to adjust my driving style, and see how that affects the Corolla's fuel mileage.

I started by coasting as much as possible. Since my drive is fairly hilly, this wasn't too difficult. Upon approaching the crest of a hill, I'd push in the clutch pedal, disengage the gear, and let the car roll.

Now that I've been making an effort to coast as much as possible, I tallied the mileage, and on my way to work, I was able to coast 12.5 miles (on a 33.5-mile trip). Coasting on the return trip home? 13.3 miles.

If I was an incredibly dedicated Hypermiler, I could probably increase this, but to be fair to other motorists, I get back on the gas when the car slows to the posted speed limit (because I'm gaining speed when going downhill).

At this point, it should be noted that many cars will not benefit from coasting in neutral. In most cases, the engine computer sees various parameters such as the throttle position and engine load, and compensates accordingly. In the case of a car coasting in neutral, the computer assumes the car is idling, and will still send fuel to the engine to keep it running.

However, if the car is kept in gear while coasting, engine vacuum occurs which makes the computer temporarily shut off the fuel supply to the engine, and thus use zero fuel.

In the case of my older Toyota, I didn't see any appreciable gas mileage improvements by using neutral versus engine braking.

The other method I employed was something else I'd borrowed from the Hypermiler handbook: turning off the car at traffic lights. I recently read that a modern fuel injected car consumes about the same amount of fuel at startup as it does idling for 6 seconds, so while I'm not shutting off the motor every time I stop, I know which traffic lights have me sitting idle for a while (30 seconds or more).

The result was a consistent gain, which brought my average to almost 38.7 mpg. This includes keeping the tires at 38psi (6 psi more than stock), shutting off the motor at long traffic lights, reducing idling time dramatically, and coasting for over 1/3 of the total round trip daily.

So if the car started at 34mpg before modifications, this means an increase of 4.7mpg by Hypermiling. Annually, this calculates to 2,688.4 miles of fuel saved equalling 69.47 gallons per year which, at $3.44 per gallon, is an annual savings of $238.98.

Next time, we'll see if it's really worth it to Hypermile.

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On a side note, I read about another Hypermiling technique in which the driver accelerates at full throttle to cruising speed, and uses engine braking (coasting with the car in gear) to slow down. The theory is that even though the car is using more fuel on the quick acceleration, it would equate to less fuel used than it would take to get the car to the same speed but at a slower pace.

I tried this technique and, unfortunately, I needed to cut the test short. After two days, I found that with this method, not only did my right knee start hurting, but it also gave me headaches, too.

Once the results were crunched mid-tank, I averaged 32.6mpg. However, this made for a miserable driving experience, so even if the technique would have done netted 50mpg, I would have probably not continued driving in this fashion.


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