Follow-up to "Fun With Hypermiling"

A few weeks ago, we at the CarGuyChristian blog highlighted our wildly successful series, "Fun With Hypermiling" which actually broke down the costs and benefits associated with Hypermiling and theories on fuel-saving techniques.

Not only did our research come up with some interesting findings and conclusions but, more importantly, it got people talking about fuel savings.

We received a lot of feedback and e-mails (keep those letters and notes coming, folks!), but one fan sent me a link that I thought was another great source of information. Plus, we like the fact that it takes some of the mystery out of internet chatter, and actually looks to replace it with intelligent reasoning. Do we agree with all of it? Not necessarily. But we do feel that giving people the information to help them think for themselves is much more valuable.

The proof? As the fan wrote me in his e-mail, "The aggregate savings at the gas station is lost by the time spent in filling your tank twice as often and at slower rates. Better to maintain your car and stop driving like a jerk." That's a man with an opinion!

In any event, take a look for yourself, and we'd love to hear what you think! Leave us a comment, or join the discussions over on Facebook.

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Fun with Hypermiling - Part 6

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
Part 6 - Is it worth it? 


So given everything that we've done, we should appreciate an annual fuel savings of $238.98. Sounds pretty good, huh? Free money, right in your pocket.

But here's where it gets really interesting.

While better fuel economy is great, the focus of my experiment was to see if the increased fuel economy is a good trade off for the wear and tear on the other items in your car that are being worn out faster by utilizing hypermiling techniques. I think it's something that all the "engineers" aren't accounting for in their reports.

Specifically, I'm thinking that with the increased tire pressure, the tires will bulge in the middle and wear out faster. When the car is put in neutral, it's using wear and tear on the throwout bearing, clutch, and transmission synchros. And when the car is shut off and restarted, there's additional wear and tear on the ignition switch, starter motor and the flywheel.

Figuring I'd keep this car about 10 years, this means that over the lifetime of the car, I'd save $2,389.80.
Being realistic, you'll need to replace the following items over the course of 10 years: tires, battery, clutch/flywheel, and starter. Conservatively figuring the car will see 15k miles per year, that's 150k miles over 10 years.

So if you owned a '94 Toyota Corolla like mine, here's how it breaks down, assuming you do the work yourself (tires are estimated, other parts prices taken from Advanced Auto online web store):

- Tires are about $320 (4 x $80) every 50k miles, so figure $960.
- One clutch - $40
- Starter - $107-$200
- battery - $60-$86

This is figured based on normal usage, so figure just for these four items, you're spending at least $1,167. This doesn't include labor to install them, and it does not include other items that may be required to be done (like flywheel resurfacing or throwout bearings for clutch jobs).

Once you start hypermiling, the wear on these items goes up considerably. For example, when driving to and from work, I would typically use the starter twice. By hypermiling, I was using the starter about 16 times. Every time the car starts, the clutch must be engaged, so that is 16 more times than normal that the clutch gets engaged. Also, as I coast in neutral, I engage the clutch to shift out of gear, then engage it again to get the car back into gear when I am done coasting. This accounts for at least 50 extra engagement/disengagement cycles. Sound like a lot? On a typical commute, I once counted 156 gear changes, just on the way to work.

Also, every time I shut the car off at a traffic light, I put a draw on the battery for things like brake lights, the radio, and then call upon the battery again to turn the starter motor. This puts additional strain on the battery, and could cause it to fail earlier in its life cycle.

I'm also overinflating the tires, so I'm putting undue wear on the center of the tread, and wearing them at a much faster rate.

So if all of these (except the tires) will expectedly wear out over the next 150,000 miles, by increasing their usage by at least 8 times their normal daily use, it stands to reason they will wear out that much faster. So, for example, instead of lasting 150k miles, they may last 20k miles. So your $107 investment in your starter just turned into a $749 investment in 7 additional starters.

And that $1,167 expense is now $2,616, which doesn't account for the increased (and unknown) extra wear on the tires which could equate to a few extra sets over that 10-year period.

So by Hypermiling, you might save $2,389.80 in fuel, but you'll spend at least $226.20 more to replace the parts that are now wearing out at a much faster rate. And that's if you buy the parts and install them yourself - your mechanic's labor fee is probably $85 an hour.

Based on the rough data, it appears that hypermiling would probably pay off if you were keeping your car for a short time (like a lease), or if you had an extended bumper-to-bumper warranty that would pay for the extra starters, clutches, etc.

Overall, I'm disappointed in the end result. I was hoping for a lot more mileage (at least breaking 40mpg) for my diligence.

On the positive side of things, I helped the environment by cutting my emissions at idle (traffic lights and coasting), I saved myself a few bucks worth of fuel, and by coasting, I learned a lot about how to take corners fast by carrying speed and not losing momentum. I was also VERY focused on every aspect of driving the car, and got better at planning maneuvers.

On the down side, it was boring (and mostly stressful) to drive so slow and methodically, and not really at a comfortable pace. The higher pressure in the tires also makes for some tricky driving under braking and on wet roads.

So it's back to normal, relaxing driving for me. It may not get me the highest mileage, but it's still respectable mpg and is exponentially less stressful!


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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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Fun With Hypermiling - Part 4

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

In Part 3, we talked about the gains in fuel efficiency by modifying the intake track on a 1994 Toyota Corolla for increased airflow. By doing this, we gained about 1mpg, for an average annual savings of 572 miles of fuel per year, which equates to 16.8 gallons. At $3.44 per gallon of 87 octane, that's a savings of $57.79 per year.

One of the tenets of Hypermiling is to increase air pressure in your tires to the maximum allowed pressure. But before you go out and do this, read on.

On the side of your tires, you'll find a "Max pressure" amount imprinted on the tire. This is the tire manufacturer's maximum rating for that tire. It may say, for example, "MAX pressure 50psi". Your vehicle manufacturer might recommend you inflate your tires to 32psi. The reason this is done is because the engineers have found a happy medium, or proper inflation pressure, for that particular vehicle.

Imagine your tires as a balloon. When you overinflate your tires, they react much like a balloon that has been blown up to a much larger size. It is very hard, but very brittle and is easy to pop. On the flip side, underinflated tires will heat up quickly, which causes a failure (blowout). These factors will increase exponentially as the vehicle's size and weight increase.

The other factor to consider with tire inflation is the shape of the tread. If you look at the front of the vehicle (and assuming you could see through the bumper), your tires will appear as approximate vertical rectangles. As tire pressure is increased, the top and bottom of the tires will bow out. This, in turn, means not all of the tire's tread is in contact with the road. This decreases rolling resistance (thus improving your mileage by making the car work less), but the decreased contact patch means less resistance for more important things like going around corners or braking. Especially in the rain. This also means the tires will wear out much faster.

Basically, if you want to play with tire pressures, do so at your own risk.

Knowing all this, I decided to go with the recommendations of Hypermilers and increase the tire pressure. I didn't have the nerve to go to the maximum pressure, so I increased the tire pressure from the Toyota-recommended 32psi to 38psi.

The result was a consistent 1.5mpg gain, which brought my average to almost 36 mpg. Annually, this calculates to 858 miles of fuel saved equalling 23.8 gallons per year which, at $3.44 per gallon, is an annual savings of $81.87.

Total savings with modded air intake and overinflated tires: $139.66

In the next installment, we'll delve into various driving techniques. You'll be surprised by what we came up with.


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Fun With Hypermiling - Part 3

Part 1 - Introduction - "What is Hypermiling?"
Part 2 - Test Hypotheses
Part 2 - Fun with air filters

In Part 2, you learned about what I'm hoping to conclude from these tests, as well as the test subject itself - our trusty 1994 Toyota Corolla.

The car typically got an average of 34 mpg with my 33.5-mile one-way daily commute consisting of about 17 miles of hilly back roads and 16 miles of stop-and-go traffic. My typical driving style could be described as "average".

The first thing I tried was improving the airflow to the engine intake. By allowing more airflow, I hoped to reduce the airflow restrictions, making it easier for the engine to suck in air (imagine trying to breathe through a coffee stirrer versus a normal straw). My hypothesis was that this would create less work for the engine, thus making it more efficient.

The downside was that with increased airflow is more oxygen. When the engine's sensors detected more oxygen, there's a possibily that the computer will add more fuel to compensate. With this car being an OBD-1 car, there was no way to read the sensors accurately, but eventual mileage would indicate the increased use of fuel.

The stock airbox consisted of a tube that ran from the front of the engine bay to a large, empty box that held the air filter. The engine pulled air from the tube, into the box, through the filter, through the airflow meter (built into the top of the box), and down another duct to the engine intake, and into the cylinders.

I removed the tube and lower portion of the box. Then, I secured the air filter to the airflow meter, which still forced all intake air through the filter.

Much to my surprise, this modification netted about 1 mpg for an average of just over 34mpg.

While this doesn't generate specific numbers on fuel use, there is the possibility that the car realized more airflow than what that 1mpg increase showed, but may have been adding more fuel to compensate for the extra oxygen.

Whatever the situation, the car consistently saw that extra 1mpg with this intake modification. The cost was free and, given the average fuel consumption rate of me and the car, would have saved about 572 miles of fuel per year, which equates to 16.8 gallons. At $3.44 per gallon of 87 octane, that's a savings of $57.79 per year.

It should also be noted that the filter was an OEM-style paper filter, so additional mileage may be able to be obtained with a higher-flowing cotton filter.

In the next installment, we talk tires.


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Fun With Hypermiling - Part 2

Part 1 - Introduction - "What is Hypermiling?"
Part 2 - Test hypotheses

In Part 1, I gave a brief synopsis of "Hypermiling".

While reading several articles on the subject, authored by journalists who had interviewed automotive "experts" on the best way to save fuel, I decided it was time for some hands-on experimentation.

I was primarily concerned with a part of the equation that I feel is being ignored by everyone - the cost of wear and tear on the vehicle (and driver) from Hypermiling. And, would it be worth it, in the long run, to practice Hypermiling on a daily basis?

Everything on a vehicle is a wear and tear item. Tires, oil, engines and the like are the obvious ones. But others like subframes, unibody chassis, even your dashboard is a wear and tear item. Plus, if you were to never even drive the car, it would still deteriorate (the rubber and plastics would be the first to go). So whether the car is parked or moving, it's still wearing out itself, albeit at different rates per component.

Some of the recommendations for proper Hypermiling include things like coasting down hills, turning off your engine, and over-inflating your tires. These would be the initial focus of my experiment.

The car that was used was a 1994 Toyota Corolla base model. It has a 105hp, 1.6 liter engine with electronic fuel injection and 5-speed transmission. The car was in good tune, with 119k miles on the odometer at the beginning of the test, and used 10w-30 regular motor oil and 87 octane fuel. The tires were 175/65-14 Toyo all-seasons with a 600 treadwear rating.

For the purpose of this test, I refilled the tank on the same gasoline pump at a Sunoco station in Wheaton, MD. I would let the pump go until it clicked off when full.

The car typically got an average of 34 mpg (with little to no a/c use) with my 33.5-mile one-way daily commute consisting of about 17 miles of hilly back roads and 16 miles of stop-and-go traffic. My typical driving style could be described as "average", though I can drive it like a rental and still manage 31-32 mpg. Not too shabby, by any means.

In the next installment, we'll start getting into the various testing methods and procedures. You'll start to really see some numbers emerge.


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Fun With Hypermiling - Part 1

With gas prices climbing quickly in response to the current upheaval in the Middle East, not to mention the annual "Summer Season" price changes, the rising cost of fuel is on everyone's mind - no matter what you drive.

You've no doubt noticed the increase of hybrid Toyotas and Hondas on the road in recent months. And as more and more people search for ways to extend their fuel dollar, there's been a lot of theories on how to do this ranging from fuel additives, to crazy gizmos in the intake track, to something called Hypermiling.

I've done some research, and while the first two are dubious at best, using Hypermiling techniques actually have some real merit and measurable results.

Hypermiling is a driving style that's used to get the most fuel economy out of a vehicle. While it's typically used by owners of already fuel efficient vehicles (there are some folks that are getting 95mpg in a Prius), it can be applied to any vehicle. The main techniques include drafting other larger vehicles, turning off the motor at idle, increasing the tire pressure to (or beyond) the tire manufacturer's recommendations, coasting in neutral, driving at or below the posted speed limit, and using a very gentle touch on the gas pedal.

There's no shortage of articles and web pages dedicated to Hypermiling (a Google search turned up over 245,000 results), and even legitimate news and media outlets will cover the subject from time to time. They'll interview automotive experts (mechanics and engineers), and discuss the best way to extend your vehicle's gas mileage.

After reading yet another interview with an "engineer" who talked about Hypermiling, I thought it was time to do an experiment to see what a real-world, "Average Joe" commuter and car owner could expect.

There's an awful lot of data, and a series of tests that I performed. So rather than writing a book here, be sure to check back for more info and results in upcoming posts.


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