How to Become a Hypermiler

The best way to save on fuel is to not use it at all - ride a bike, use mass transportation, etc. However, there is a rather large subset of the population that live in a suburban prison. The following is a set of techniques used by people that call themselves hypermilers to achieve high fuel economy/efficiency (FE) numbers, save the planet and save their wallets.

Step 1: Tires

Inflate your tires to, at least, the maximum inflation pressure to reduce rolling resistance.

Should you wish to go beyond, that is up to you. Personally, I inflate my tires to around 55psi (they are rated for 44). Please do not attempt on old or visibly damaged tires. My tires are new and in excellent condition.

Modern tires are radially belted - that is, they won't balloon like tires of yore. Keep in mind what you're doing though. You are reducing the contact patch of your tires in order to decrease static friction. This will reduce your overall braking ability. So riding someone's bumper at 80mph is just that much more dangerous. Again, these steps only work when combined - you can't pick and choose.

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When it comes time to buy new tires, look for low rolling resistance (RR) tires. While they may not have the same 60,000 mile (or even 40,000) guarantee, they will save you in the fuel department. The Toyota Prius comes equipped with LRR tires.

Comments

[jimmytvf]

I don't agree with the alternator feature. the alternator loads the battery, and doesn't need more power to drive all the electric features, the battery does the job as well. Yes, the faster the alternator goes, the more power generate, and goes to the battery.

[mrdoc]

Please don't spread rumors for what you don't know!

When the car is moving down the road the alternator runs ALL electrics in the car, AND recharges the battery. It ususally only takes a short time to recharge the battery, then that part of the alternators use is done.

The batteries sole purpose in life is to start the car. Once started you can remove the battery and car will run just fine and as long as you don't turn it off will run just fine for as long as you want!

UNLESS you've added additional electrics to the car, and I mean a lot of additional electric to the car, the alternator can power them just fine, there is no "big" load.

All the voltage generated that is not needed by the car/electrics are truned into heat and dissipated into the air. More speed does not mean more voltage generated, thats taken car of by the voltage regulator. The regulator keeps the top voltage output caped at 14.5 approximitely. After a few thousand rpms the output of the alternator does not increase, it stays constant. Same output at 30 as at 80mph.

[trebuchet03]

Generally speaking - the battery is only used while starting. Alternator output will match the load requirement from all electronics from the car. The alternator is capable of delivering more power at a higher RPM but will not deliver if the load does not exist.

A battery is not an infinite sink of energy storage. You can't add more energy to a "full" battery without damage. Grab an ammeter and measure yourself (I would recommend a clamp on inductive type rather than a shunt ammeter as the current flow during starting will be very high).

If you have the opportunity, I highly recommend auditing an introductory course on electrical engineering at a local university. Particularly lessons on Kirchhoff's Circuit Laws (loops and whatnot). I was Mech engineering but really loved the electrical engineering bits :)

[sthomas28]

trebuchet03 I'm just getting on the scene here, doing some research. I'm giving a lot of weight to your comments. You seem to know your stuff. It looks like you and another poster were speaking around each other. I think the other poster has it mixed up a bit, in that an alternator and typical electric generator/electric motor work a bit differently. Specifically where "Magnets" are concerned. Please correct me if I'm wrong.

If I'm correct, as are you, the increased spinning of the alternator will not increase output. It's not the input spinning that's the factor but the load placed on the alternator. The alternator will meet the load without an increase in the input rotation.

Again, please correct me if I'm wrong. Do know if you'll see this but if you do I'd appreciate your response.

[jimmytvf]

they have some voltage regulators inside that keeps a constant voltage no more than 14v

[jimmytvf]

that's what i wanted to say, when the battery is full, it have enough power to run any electric device you want, and doesn't mean any fuel consumption, because the alternator is always running. I'm spanish and i don't even know to express myself in some ways, and i'm a automotive technician and we learn Kirchoff's law too. Have to take a look, because i have some aspects that i don't remember, 3 years have been passed since that

[trebuchet03]

You're somewhat familiar, excellente! If we were to represent the vehicle loads (computers, lights, valves, etc.) as one single load for simplicity - we could draw the circuit diagram with three components in parallel. Those components are the alternator, the vehicle loads and the battery.

The alternator is source, the battery can be represented as a capacitor as it is near full and the loads can, for simplicity be represented as a resistor (lets not mess with inductance).

Before the car is started, the battery is around 12.5V

When the vehicle is started, current flows from the battery through the loads and bypasses the current source.

Next, the alternator takes over. The voltage off the alternator is higher than the battery (13.8-14.5V or so). Current flows into the load. Because the alternator's voltage is higher than the battery, current can also flow into the battery. As the battery voltage increases (as it will for this chemistry), current slows down until the voltage equalizes and current can not flow. This is why we can represent the battery as a capacitor. When a capacitor is fully charged, it is effectively an open circuit.

From this point on, current flows from the alternator to the load and bypasses the battery (as it is "open").

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Now, an 80amp rated alternator does not always put out 80A. If the load only calls for 10A, the alternator only puts out 10A. We can not have this equation out of balance (energy in must equal energy out + entropy losses). Simply, the current that goes in must be consumed. When the car demands more current, the alternator supplies it and in turn the alternator requires more torque from the engine to turn.

More torque means more fuel consumption. With an instantaneous fuel gauge, this can easily be seen be comparing idle fuel consumption with little electrical load to fuel consumption with as much load as possible (high beams, defroster, vent fan without a/c, brake lights, hazard lights, power windows in motion, etc.)

[jimmytvf]

The amperes become through the resistance of the material (more loops on the alternator), doesn't mean more torque. The engine has the same torque all the time (crankshaft, camshaft, and so on) are spinning with a minimum torque when it starts, the torque is only needed for the wheels to keep on the ground, excessive torque=wheelspining you don't want an alternator do this.

http://automecanico.com/auto2002/alter4.jpg

alternators work like engines, there's minimum friction, only for + and - contacts ( they have to spin to connect the wires obviously)

NOW, what you want to do, is turn, for example, water pump, fuel pump, the engine fan and so on, running electric, that will be less load on the engine and the alternator is capable enough to run all this elements, is designed for this use, A/C, the stereo, airbag control system, fuel injection... everithing is going with current nowadays and brands desing better alternators to handle up this loads. (Toyota prius, for instance, nuff power to pull out their own motors that are the alternators itselves)

[sdfgeoff]

I went driving one day in an older, low powered car. We were towing a caravan, and the car was jjuusstt coping with slight ups and downs. Then, when it got hot (we had started in the cool morning), we turned on the air-con.
Yup, aircon does make a difference. Now we could only tow it on the downhill, and acceleration was pitiful.

The load on the alternator does effect the strain on the engine.


And, if you want to prove it to yourself, grab a cheap DC motor. Spin it, see how easy it turns? Now solder a wire across the two contacts (shorting them). Now it is a lot harder to turn. The wire simulates a huge load, like what radios and air conditioning will place on a cars alternator.

[M0HIZ]

Correction: air resistance/drag goes up as the velocity squared, not cubed.

[Outlander]

No real pay off here. My old 87 Oldsmobile cutlass achieved 21-23mpg highway with a carbed 5.0L V8. This is one of the most non-aerodynamic cars ever made, but! A new V8 dodge charger only gets 17-18mpg. Something most likely a lot more "aerodynamic" than an old square 4000 pound muscle car, but yet it achieves even less fuel mileage. One the of the most aerodynamic cars, the smooth looking mid-late 90's camaros only achieved 24-28mpg. Aerodynamics has very little to do with MPG unless one is planning on driving 200 MPH. Sorry to be a negative Nancy, but it's true.

[hellinabox]

Aerodynamics don't matter until 200mph!? Try riding your bike behind a semi and then against the open air.

[jimmytvf]

LMAO but true. that's why bike racers on Tour de France wear those helmets and not a block shaped one

[trebuchet03]

Once 4000 pounds of car is no longer accelerating (say you've stopped at your cruising speed of 70mph), it takes no additional force to move the mass of your car EXCEPT that of resistance forces coming from: 1) Rolling Resistance 2) Aero Resistance Ride a bike on a windy day and tell me that aerodynamics doesn't matter. You're comparing different cars, with different power trains and making a link to aerodynamics. That is what's known as a fallacy ;)

[Outlander]

Not true again. an 87 olds cutlass vin 9, and some vin y's used the 4 speed overdrive 200-4R. Every single GM car has used the 200-4R and 700-R4(a less efficient but tougher trans.) since the late 80's up until the early 2000's The 4L60 and 80's are nothing more than an electronically controlled 700-R4. As for the engines, not much has changed, still 5.0L, 5.7L 90deg roller V-8. The fuel, electronics and induction has changed over the years, but still the same. Simply look at the EPA rated MPG figures for each. There is no major change, or difference. On some models there has been a change for the worse. As with the 4.6L ford. The fuel economy has dropped since going from the 5.0L going to the "modular" 4.6L. No real positive change. hope that makes some sense for you.

[Rishnai]

So, basically you're saying that if electronic engine control really makes milage better, or at least wasn't just an unnecessary complication, then a more aerodynamic car should not have lower rated milage, am I reading you right? Two things have changed: engine control and car shape. So assuming that the new engine control is better, it must be the car shape causing the lower milage. But since we know from experience that wind resistance does actually matter, we may have just proved that most electronic engine management is all smoke and mirrors. Another possibility is that you're quoting sports cars, which are generally tuned for downforce. Of course, downforce gives you more grip, but robs your straightaway speeds and fuel economy, which is especially obvious in stock car racing. I do know, though, that my dad's '93 Olds Cutlass gets embarrassingly close to a brand-new Milan's milage, with more than 120,000 hard miles on it's clock. There's something amiss there from a technology standpoint.

[trebuchet03]

So you're saying your 87 cutlass has the same shape as a charger and camero and the same exact power train (mind you, electronics is an integral part) - and then go on to say the changes that have been made (and some not so good). Honestly, I don't care about what changes have been made over the years - if they are not identical, you're practicing bad science. Again, when you want to make a link to aerodynamics - control everything, except aerodynamics. Here's a perfect example - the TV show myth busters did a bit on Tailgate up versus down. They took two identical vehicles (brand new, same mileage), then had one tailgate up, and one down with rules fro driving technique. Same power train, a best effort to control driving technique, two different aerodynamic configurations and a full tank of gas. 800 or so miles later, the truck with it's tailgate down ran out of gas - the other truck ran out of gas around 40 or so miles later. Later, it was empirically tested with a fuel consumption meter -- again, tailgate down consumed more fuel.

[IfWeChoose]

 OMG, if aerodynamics didn't make a difference then why is there such a term?

[ColoradoCyclist]

True, if you look at any race vehicle you will see any or all of the following: 1) a spoiler, this is a airfoil that uses the wind to keep contact to the road, why because the natural aerodynamics of a car suck and that mostly is from air going under the car which leads to the next item. 2) a splitter, this is a curved gap filling board of sorts, this is used to get the vehicle as close to the ground and diminish the gap, or reduce drag and improve aerodynamics. So anyone that says aerodynamics is fake or doesn't work..... well haha go on paying for gas as we pass you at the gas station..... haha

[jimmytvf]

that's what i'm talking about, playing with throttle and RPM. Low rpm = low fuel --> FALSE Low rpm make the time lapse between injections increase, so we get less fuel in a second, that's true, but, if we have to step more the throttle to get the same rpm, the volume of fuel increase, and the car needs energy to move and spend more fuel. you have to play with what your engine needs and, at the same time, manage the efficiency of the fuel you send to the engine

[jimmytvf]

best rpm shiftings on petrol: 2000 to 2500 RPM
best rpm shiftings on diesel: 1500 to 2000 RPM (lower rpm torque point)

[trebuchet03]

To your earlier comment - this is why instantaneous fuel economy data is important ;)

Yes, we care about long term average consumption - but you won't get good long term averages if you can't keep your instant consumption low (as you accurately said: "play with what your engine needs").

[jimmytvf]

yes, i've just realize about that ;)

[ac-dc]

There are so many things wrong with this instructable I don't know where to start.

Do not over inflate tires. It is dangerous, should be illegal and might be, will wear them irregularly in the middle regardless of being radial belted. The proper inflation level depends on the vehicle weight and is usually stamped on the the vehicle door sticker or elsewhere.

Seats don't usually weigh 100+ lbs each, even if they are motorized, not even a full bench rear seat.

There is nothing to "tune" on a modern fuel injected, computer controlled engine. It's sort of a myth perpetrated by youngsters repeating what old timers said back when engines could be tuned manually without reprogramming a memory chip.

It is very ill advised and dangerous to suggest not using air conditioning (heat delirium while driving causes accidents), or defrosters (which you'd only use to get rid of frost, it's illegal to not keep visibility by choosing not to use a defroster when needed). Further, if you can't see traffic or traffic control lights, signs, etc, due to frost or fog you can't plan your acceleration and deceleration as well.

One thing not mentioned was that on some vehicles you can change the vacuum tube configuration to make the AC system blower blow out the defroster ducts without it in defrost mode so you can clear windshields without running the AC compressor and incurring the additional engine drag, but be sure to keep the vac system a sealed system as an open (leak) will cause CEL to come on and you'd be in the inefficient computer open loop mode in many cases.

Pulse and Glide driving is not proven to increase mileage in general, only with hybrids and certain ICE vehicles. With most (other) vehicles the more effective driving is to accelerate at the engine's peak efficiency RPM then maintain approx 40 to 45 MPH, or the speed limit if it is lower than 40 MPH. This in fact _has_ been proven constantly to have better fuel economy. Pulsing up to speed again is "usually" less efficient than maintaining the average speed. Of course certain engine and transmission combinations can change this, but it was suggested as if it's always an improvement to pulse and glide when it isn't.

Constant throttle up a hill does noting to improve fuel efficiency. Keeping the throttle varied so the engine always stays within its peak efficiency RPM is more fuel efficient.

Engine off coasting may be illegal, but it can be done safely if the driver is either very strong/small car so steering effort is manageable, or it has electric steering so the battery is enough of a reserve to power it. Brakes are the same thing, there is reserve pressure for one stop or pumping can build it up, but of course either is still less safe.

The suggestion about 50-75% throttle is only valid for small cars with anemic engines and matching gear ratios/shift points, with no traffic around. Otherwise you could be accelerating too fast, unsafely and putting stress on the vehicle and tires. Often if you accelerate a little slower, you have more time to react to road conditions or vehicles ahead of you. Point is, the exact situation changes which acceleration strategy is most efficient.

Blocking your grill has not proven to be effective, except on select vehicles! You're making blanket statements that are incorrect a large % of the time. It is not just a matter of reducing drag or cooling system temperature, it is a matter of how the computer changes engine fuel air mix due to the temperature of the engine. Sometimes it helps, other times not. It will have to be tested per each vehicle and also with different driving speeds and ambient temperatures. Also, most cooling systems rely on electric motor(s), it causes more alternator load to block the radiator.

To summarize, sometimes these strategies help but other times they not only don't help but increase vehicle wear, risk of an accident, road rage from other drivers, and are illegal. It is no more reasonable to break laws to save gas than to break laws because you feel like robbing a bank to buy more gas. Vote to change things, and petition your government representatives for change.

[jimmytvf]

just look at the tyre that's on the picture, is like a ballon, overinflated and blown up

[jimmytvf]

the side skirts and the belly pan are true, but i won't let the engine overheat for blocking the grille. The engine before the fuel. That's the first law of efficient hypermiling. Close the mirrors is even more unaerodynamic, are more flat sided than the rounded edge mirrors as if, and you'll may be fined too

[trebuchet03]

Cooling systems are extremely overbuilt to hand a scenario that includes driving through a desert (45C+ with very low humidity) under high loads (heavily loaded car, a/c on, windows down, etc. etc.).

If those are the conditions you always drive in - you potentially can't afford to cover. Otherwise, if you're driving in 20C weather - the thermostat is going to stay mostly closed to reduce coolant throughput.

From a heat transfer standpoint - you want to keep the engine at a relatively static temperature over a dynamic range of environments. In hot conditions, you'll need high airflow and high coolant flow. In "normal" conditions you can either have lower airflow or lower coolant flow. In cold conditions, you want both lower airflow AND lower coolant flow. Unless you're in that desert/high load class - you don't need 100% efficacy (mind you, that's not efficiency).

[jimmytvf]

i'm talking about traffic jams that the engine in idle needs some refrigeration and if you block the air intake of the fan, the car overheats, because there's no other kind of air running through it. In highways, you're not idling, youre often running at 3000 rpm, and it generates even more heat, and if you block the air intake, the air coming through the radiator wouldn't be enough to cool the engine as designed. combine that with a fan that recirculates hot air through the engine. combine that with daily driving like running a/c and carrying people on your car like children and the daily shopping. That's not extreme conditions (the desert is), is daily driving

[trebuchet03]

If you're in a traffic jam.... There's no airflow anyway ;)

"youre often running at 3000 rpm, and it generates even more heat, and if you block the air intake, the air coming through the radiator wouldn't be enough to cool the engine as designed."

Firstly, heat generated is independent of RPM. Heat and load are correlated. It's a minor caveat - yes, on the highway, you will have more load than when idling.

Secondly - my earlier post stands. The cooling system is way overbuilt to handle desert conditions running all of these accessories (a/c, carrying people, cargo, etc.).  If you're not in a hot climate - you don't need all of the cooling capacity that the factory installs.

I operated my cars in South Florida where temperatures would frequent 35C - I had no problems. My car warmed up faster and temperatures leveled off around 95C (within the operational zone of specified by the mfr - in my case, Volkswagen)

I, among others, have not had issue. Blocking off the front of the car does not hermetically seal off the entire system ;) You still have some flow ;) As I said in the instructions - monitor your coolant temperature and adjust accordingly :)

[jimmytvf]

"If you're in a traffic jam.... There's no airflow anyway ;)"

yes, but you force the fan to push more air than expected. The air cavities are designed to make a correct air flowing.

"Firstly, heat generated is independent of RPM. Heat and load are correlated. It's a minor caveat - yes, on the highway, you will have more load than when idling."

no. at more RPM, the more strokes you make, more explosions in the cam. that's why injection cutting was invented, to prevent overheating due the high RPM (yes you won't cut injection all the time, i'm talking about an emergency issue) and is more dangerous 3000 rpm when idling than on the highway (you have the fresh air that cools the engine to run properly)

"Secondly - my earlier post stands. The cooling system is way overbuilt to handle desert conditions running all of these accessories (a/c, carrying people, cargo, etc.). If you're not in a hot climate - you don't need all of the cooling capacity that the factory installs."

not so overbuilt as you think. people that live in the desert usually have issues of that. If you see tv show Extreme Trucking, all the grilles are blocked up to keep some warm inside. too much warm will be harmful for the engine

"I operated my cars in South Florida where temperatures would frequent 35C - I had no problems. My car warmed up faster and temperatures leveled off around 95C (within the operational zone of specified by the mfr - in my case, Volkswagen)"

you say 95C? 100C is the temperature of boiling water!. Agree with the coolant could handle 120C but is better have a little margin. That's why coolant is designed this way. the perfect temperature is around 80-85C

"I, among others, have not had issue. Blocking off the front of the car does not hermetically seal off the entire system ;) You still have some flow ;) As I said in the instructions - monitor your coolant temperature and adjust accordingly :)"

agree, but all of this will harm your engine. maybe not today, maybe not tomorrow, but the engine is not designed to handle this. sometimes is better spend a little more fuel that a brand new block

[ac-dc]

Your statements seem to imply an engine is hotter on the highway than idling, which is not necessarily true. On the highway at a constant fuel efficient speed, the air passively rushing through the radiator fins can more than make up for the higher load and RPMs.

Heat is not independent of RPM. They don't change linearly with respect to each other, but at the same load a higher RPM will cause more heat... although you might have to swap in different gear ratios to achieve this in the same vehicle for testing.

That the cooling system is overbuilt is not a proof that it will stay within margins when it is altered. It is certainly possible, since the fans would be running more often or faster (or 2nd fan kicks on in cars with two fans), but each vehicle design including different engine configuration per, would need tested.

[crispy010]

The reason P&G may get you better mileage at low speeds is because the engine is operating so far below its peak thermal efficiency when powering the car at those speeds. Put another way, the car has too much power. Peak thermal efficiency is, as I think was stated above, around 75-85% of full power. To get maximum mileage while still being able to cruise at highway speeds, all cars should have about 65 hp (in general, it takes 30-50 hp to cruise at 65-70mph). However, turning your car OFF while moving is a BAD idea. When the car is off, your power steering and brake boosters no longer function. This essentially means your car becomes a 3000 lb uncontrolled brick on wheels. Please DO NOT turn your car off while moving. Shifting into neutral will get you most of the efficiency benefits. Additionally, turning your car on repeatedly will wear out your starter motor, battery, and electrical system - they are not designed for that many cycles. Even in hybrids such as the Prius, the gasoline motor is "bump started" instead of being turned over by an electric motor.

[vandal1138]

People also don't realize that the amount of gas utilized in starting the motor is greater than leaving it running for the time being, so unless you are coasting down a LOOOOOOONNG hill, you're wasting gas by shutting off the engine and starting it back up again.

[xaenon]

The rule for carbureted models, if I remember, was 'shut it off if you're going to idle more than about five minutes' - the five-minute figure being based on the idea the engine would use as much fuel at restart as it would 'waste' idling for five minutes. All assuming, of course, that everything was working as it should, which with carburetors, was not all that often the case.

With modern fuel-injected cars (port-injected in particular), the amount of fuel required for restart is far, far less - enough that you'll actually save fuel if you shut it off and restart it when needed, rather than let it idle for TWO minutes.

[V-Man737]

Really old cars use a lot of gas on startup. More recent models (1996+, I think) have really cut back on that. Turning off your engine is quite effective, if it is new.

[Dude567]

Yes but in the first 90s of your engine running 75% of the pollution is emitted because a cold catalytic converter is not very efficient

[ac-dc]

It's not going to be very cold, there aren't long enough periods the engine would be off for it to cool down that much, and if you were implying that it takes 90 seconds to warm up, no it does not, the thin honeycomb structure in any recent vintage cat. converter heats to temperature far faster. For once, greed on the part of manufacturers to reduce the amount of costly precious metal in a cat. resulted in several useful gains.

Modern engines can be designed so that their emissions stay within EPA mandates for pollution, haven't you noticed some street legal cars now do shut off their engine when they are stopped (stop light, etc.)?

[swander]

This is a joke. If you dont have a hybrid or electric car, this pulse and glide is a wash. Take a carbureted car for instance: Every time you mash the pedal, you are squirting up to 80cc of raw fuel into the carb (Holley 850 DP with 50cc pump on rear) This is an extreme example but it is a valid concern. This fuel is way more than is needed to combust so you get the telltale black puff out the rear. Keeping a steady rate will net more mileage than this dangerous illegal practice of turning the motor off or varying your speed 25% on a shared road.

[swander]

you wanna get off the alternator entirely? Just disconnect it. Youll run off the battery for at least 30 minutes and you can just recharge it when you get home. Saves gas but not your battery or your electric bill. A/C Use is also somewhat of a myth as many cars use the A/C system to recirculate cabin air. Even when the car is not using the A/C to cool, its still running. I did a test on my cars mileage computer going to work one day (40 miles RT) with A/C cooling and then no A/C cooling. Same exact mileage. You really want to reduce drag on a motor? use an electric water pump. The water pump is like a mini dyno, the faster the car motor revs, the more power is required to turn the water pump.

[swander]

You can no longer get your car scanned for free at Autozone in CA, seems the garages were losing too much business, so they lobbied a law against that. Use the lowest numbered oil your car can take, like a 0w15, this is thin oil that is designed for warm climates.