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With the price of gasoline up over 40% since the beginning of the year, many people are trying to find new ways to save money at the pump.
While many of these ideas are useful and worth the extra effort – i.e. adjusting your commuting time, cleaning out your car’s trunk, turning off your car at long stop lights – many driving habits that people think will help them save gas or money are actually causing them to waste both.
If you really want to monitor your fuel economy, buy a ScanGauge digital fuel economy gauge.
So on that note, here are the top four ways people think they’re saving money and/or gas when they’re actually not:
- Driving across town to save a nickel on a gallon of gas. With gas prices at record highs, many people are doing everything they can to reduce the amount of money they spend at the pump. One of the more popular ways people are doing this is by using sites like Gasbuddy.com to find the cheapest gas stations in their zip code. Unfortunately, many of these same people are driving long distances to save a couple of pennies on a gallon of gas – meaning they’re probably burning up the amount of money they save by using extra gas to go to an out of the way station.
- Driving on the highway with their windows down to avoid using the air conditioner. We’ve become accustomed to thinking that our car’s AC is the biggest drain on our car’s gas mileage. While using it will reduce your gas mileage, there are many instances where using your AC instead of rolling down the windows will actually be better for your car’s gas mileage. One of the biggest drains on your car’s gas mileage is aerodynamic drag – something that is exacerbated by rolling down the windows. If you’re going to drive on the highway, go ahead and turn on your AC and keep the windows up!
- Driving with their truck’s tailgate down. Many people believe that driving with their truck’s tailgate down will improve gas mileage. Unfortunately, the opposite is actually true. When a truck’s tailgate is up, a “protective air bubble” will form in the bed area which actually makes the truck a little more aerodynamic; when the tailgate is down, this bubble disappears and gas mileage gets worse.
- Accelerating extremely slowly. Many people think that the slower they accelerate, the better gas mileage they’re going to get. Unfortunately, extremely slow acceleration can bog down your engine and make it run less efficiently – thus wasting fuel. So, instead of slamming the accelerator to the floor or barely even touching it, try and find a nice happy medium so you can achieve a moderate acceleration.
So, if you’ve been doing the aforementioned items, I certainly can’t fault you for trying to save gas and money, however, there’s a reason why you haven’t seen much of a savings – these ideas just don’t work.
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yeah… the A/C one is totally wrong. I’ve done tests with my vehicle and the difference is dramatic. The A/C gobbles up gas. Windows don’t. If you need more proof see the mythbusters episode where they test that exact theory.
You forgot “Drive the speed limit”.
Many people have heard that for each 5 mph over the speed limit you go, you add 20 cents per gallon. The gas mileage of a vehicle is not dependent on the speed limit of the roads, rather the speed of the vehicle. If you go 60 mph, you use just as much fuel in a 55mph zone as a 65 mph zone. Most cars reach peak efficiency at around 60 mph, while trucks and SUVs reach theirs around 85 mph. It’s still wise to experiment with your vehicle to find your peak as opposed to guessing or living in ignorance.
“Most cars reach peak efficiency at around 60 mph, while trucks and SUVs reach theirs around 85 mph.”
With hands clutched tightly, forming “fists of rage,” I, the Mighty Obbop, star of neither screen nor stage and a dweller of http://www.bannination.com, screams to the world, “Huh?.”
How oh how can any logically-thinking humanoid dare to proclaim that “peak efficiency” occurs at a speed offering less of those little mpg things than driving at a lower speed?
Over the decades, a multitude of folks with better minds than I (this includes sundry cartoon characters) have asserted that various algorithms (Al Gore rhythms?) indicate the most fuel efficient speed is with 45 of those little mph thingys.
If thou disagreeth meet me at the bike racks after school.
Jesse – that’s not entirely true:
http://en.wikipedia.org/wiki/MythBusters_%28season_2%29#AC_vs._Windows_Down
http://en.wikipedia.org/wiki/MythBusters_%28season_3%29#AC_vs._Windows_Down
Like everything else, there are a lot of variables, but it seems to be show that the faster you’re driving the more having your windows down saps your car’s gas mileage.
“the most fuel efficient speed is with 45 of those little mph thingys.”
Engine effiency is based on engine load and RPM. Assuming a flat road and constant speed, you get a speed/effiency curve for each gear the car can be in. On a normally aspirated car, this usually looks like a bell curve, with one maxima. So, for any gear, you have a most effient speed, with the higest gear usually being the most efficient overall. For some cars its 45, others 60, and some even higher. If you have a forced induction car, e.g. turbo or supercharger, the car may have more than one peak effiency point.
Fuel efficiency relates to your rpms.
Period.
The lower you keep your revs, you WILL save gas.
Coasting when possible is good.
Keeping your momentum going is good.
/ gets 33mpg in a car rated for 28
Obbop,
Geez. I didn’t mean to start a schoolyard fight (?) or anything. I was just commenting that there wasn’t some sort of magical forcefield that deducts fuel efficiency if you exceed the posted speed limit.
Perhaps the term “peak efficiency” was used out of place, but crikey. IT was the term that my team used in GM’s Challenge-X (that alternative-fuel SUV project), and our control truck (market engine) peaked at 77 mph in the simulation program.
rubens hakkamacher: BS, BS, BS. RPMs have almost nothing to do with the amount of gas your using, its almost completely dependent on how far your gas petal is pushed down. When you let go of the gas petal, even if your RPMS are still at 3000 you will use NO gas (on a fuel injected engine) because the wheels are keeping your engine turned over and you don’t need gas.
BTW the you lose efficiency going over the speed limit has some truth, in so much that going over the speed limit greatly increases your chances of needing to suddenly brake. Generally speed limits are set based on such things.
The best way to save gas — keep it under 2,000 RPM. Want to see where your gas is going? To hell with the speedometer. Watch your tachometer. No matter how fast you go (but always obey the speed limit), keep it under 2,000 RPM and you’ll save more gas. Some cars can go up to 80 MPH (my vehicle, for instance) while staying right on 2,000. I know other people who can only do 65 MPH while staying at 2,000. Either way, you’ll be saving gas. Higher RPMs means your engine is burning much more gas to to stay at that constant MPH. Find out how fast you can legally go while keeping it under 2000, or between 1500 – 2000, and do that speed. If it means leaving a little earlier to get there on time, wouldn’t it be worth it considering the amount of money you’d be saving?
As they stated on the aforementioned episode of Mythbusters, the amount of drag increases with the cube of the speed, which has to be taken in to account along with the horsepower curve of the engine to determine the optimum speed.
John
“Generally speed limits are set based on such things.”
Um… no. Generally speed limits are set by arbitrary political factors and population density formulas, not engineering, physics, or other such ‘science.’ There are cases where speed limits are set appropriately, however those are mostly entirely by accident.
You are correct in your assertion that heavy braking (typically followed by heavy acceleration) are the true bane of gas efficiency. Next time you’re in a parking lot or stop light, check out the rims of the vehicle s near you. Vehicles with lots of black brake dust on the front wheels (for awd and fwd) are the most egregious offenders. Leave some space, use your transmission for slowing yourself down, your brakes are there to stop you.
Of course, the prevalence of automatic transmissions makes all of this moot as most drivers are mindless drones simply pointing and shooting their way too and from work.
My F-250 gets it’s best mpg when it’s loaded to the gills with family and luggage and hauling butt at 80mph. I’ve also discovered that some vehicles get better mpg on gas from a particular station. My truck likes Shell and Texaco, while my car seems to like the local station called Zoom’s, which gets its gas from a local Giant refinery. Over a few years, I’ve noticed a 2-3 mpg difference when I buy my gas at the right place.
I’ve tried the smooth and gradual acceleration, driving the speed limit, etc., and it really never made a noticeable difference, other than having other drivers flip me the bird.
Although you may spend a few extra cents going to the cheapest gas station in the area, I would suggest that we all do just that. If we continue to reward gas companies with our business just because they are closer and ‘convenient’, in the long run we are admitting that we don’t mind paying higher prices.
Use gasbuddy.com and actively avoid retailers that are in the top 10%. Make a point to drive accross town. They lose the business from the snacks, cigarettes and other purchases as well. Do your best to reward those who keep their prices low.
I think a lot of people forget that the gas pedal isn’t the only pedal that figures into the mpg equation, but the brake pedal also plays a role. If you find yourself constantly having to firmly hit the brakes, you’re wasting the momentum that was just built up by your engine, while burning gas. For instance, if you accelerate from 0-60 in 7 seconds, then find that you have to hit your brakes hard to slow down for a car in front of you, you just wasted a lot of the gas that you burned to get you up to that speed to begin with.
Like everything else in life, moderation is key. Use the accelerator moderately, use the brake pedal moderately, and find a happy balance betwee them.
i have a 2002 hyundai elantra. if i set cruise control at 60MPH with AC on, i get 32MPG. at 75MPH with the AC on, i get 28MPG.
at 45MPH with the AC on, i get 27, unless i get out of OD. i set the car in third gear and it actually gets a bit better mileage. the trick is to keep it between 2000 and 2700 RPM.
but that’s just my type of car.
To hell with the speedometer. Watch your tachometer. No matter how fast you go (but always obey the speed limit), keep it under 2,000 RPM and you’ll save more gas.
Yeah! To hell with science and the physics that govern internal combustion engines…with all their variables like valve timing, etc, that govern the RPM at which your engine operates most efficiently! YEAH!!!
Hey Conundrum…what if the gas station that sells cheap gas jacks up their cigarette and beer prices? THEN what do you do?
rubens – it’s about injector pulse width or throttle plate twist depending on whether you’re injected or not.
when I am going 145mph on the freeway my mileage is less than 6.0, but my car wont bother calculating it lower than that
Gas mileage is actually simple, but it’s based on complex issues.
Other posts have hit on some of the issues, but it involves many factors.
Are the tires inflated properly?
Type of tires?
Is the vehicle body dirty?
Engine horsepower?
Weight of vehicle?
Weight of cargo?
Fuel/air mixture properties?
Cylinder(s) and combustion properties?
Aerodynamics?
Vehicle size?
Gear ratios?
Drivetrain components?
Transmission type?
etc, etc….
All things being equal, a drop of 90 octane gas has a set amount of energy within it to move a respective mass, which no amount of wishing can change, period.
I’d also note that all gasoline is initially created equal, the difference arises with which retailer has what detergents or other additives put in it to disginguish themselves from the others. Additives may help keep your engine/fuel system cleaner, but do nothing to create energy.
Gas mileage is bound to vary depending on all the above and then some.
I would generally agree that the lower the RPM’s mixed with the higher gear ratio, lower drag coefficent and lower vehicle weight will yield the best mileage.
I would also agree with one of the posters that 45mph is the optimum
speed for many vehicles, however unpracticle that may sound in some circumstances. Most people don’t have a Ferrari. And that utilizing coasting techniques with a manual transmission and minimal braking also helps.
Anyone that says different, either isn’t being truthful, or isn’t/can’t test all the various factors in total precisely enough.
just walk, it will save you a crap-ton
Some of you guys have a lot to learn about internal combustion engines and thermodynamics. Your ultimate gas mileage is, as John sort of stated in post #8, determined by your throttle position and speed. How much gas are you using v/s how far you’re going. That’s all there is to it. RPMs are a simply a byproduct of throttle position, engine load, and gearing. RPMs alone are NOT a good indicator of fuel economy. If you’ve got your throttle wide open, but you’re trying to chug up a hill in your top gear staying under 2000 RPM, do you really think you’re saving gas? Hell no, you’re drinking it like it’s going out of style
If you really want a good indicator of fuel economy, install a vacuum gauge on your dash.
Driving across town to save a nickel on a gallon of gas.
I partially agree/disagree with this.
Going across town just to get gas that’s cheaper isn’t worth it.
However, combining the trip with other errands that are also across town will make it prudent.
Such as getting gas at Costco when you shop there.
Gas, what’s this gas you speak of? Mmmm Bio-Diesel.
I do AC on the highway and windows down on country roads. One thing people always mess up on is that you should drive the route that allows the most constant motion. My commute to work is 23 miles by highway and 20 by roads but on the highway I set my cruise control and go. On the regular roads I would be stopping and starting.
So if the RPM theory is true, then my 1 ton Civic at 3,000 RPMs at 65mph is less efficient than my 2.5 Ton F150 at 1500 RPMs at 65mph. That’s good to know!
/had no idea so many people failed High School Physics.
buy a hybrid. We just got a new Toyota Prius–first tank of gas (around-town driving) was 58.2 MPG. And it is a nice car, with more room inside than would appear from the outside.
I don’t use gas buddy, but being on the border of NY with NJ, I always drive down to Jersey to get my gas, it’s always at least 15-20 pennies per gallon cheaper there.
Driving across town to save a nickel? It may not make sense in the short term, but it makes lots of sense in the long term. It is the only weapon available in the fight against greedy oil companies. Withhold business and shop the best price.
Why worry about it, my 7 liter engine is going to suck down gas either way, might as well enjoy it. beside al gore created the internet, he will solve global warming in his sleep while hunting down oshama
Like people said above, with manual transmission coasting down a hill or any type of incline is good for gas. I’m not sure if this is true or not, but if your car is turbocharged, you lose mpg when you start boosting, it’s something I’ve noticed but don’t know if it’s true.
Chris speaks truth in #10. The force of drag on any object is D = ½*r*Cdp*A*V², where r, Cdp and A are constants (density of air, coefficient of drag, cross-section area) and V is velocity. This means that drag is a function of V² and since power is P=F*V, power is a function of V³.
It may be true that engines are more efficient at a specific RPM (I don’t know), but that doesn’t really relate to velocity because you could always change the gearing, and anyway the difference is insignificant compared to that V³ factor.
We just bought a 2007 Toyota Prius (top of the line) and a 2007 Toyota Yaris Liftback (manual). Even if you get the Prius entry level (or thereabouts), the smarter buy is the Yaris (or even the Corolla). Once you start computing the actual mileage off the actual gas for your Prius (as opposed to the in-dash MPG display), you will find you drop down around 45-47 mpg. The $10K+ cheaper Yaris will buy alot of gas to offset the 5mpg difference of the Prius.
However, if you are in chronic stop-and-go traffic in your morning/afternoon commute, then the Prius will deliver more like it should (50-60 mpg).
Tt
IF you want to save cost by using less gasoline, SLOW DOWN For ever MPH above 60 wind resistance increases proportionately, and gas economy suffers.
Traveling at 55 down to about 40 give you the highest bang per buck. Slower and RPMs produced by the engine has to work to pull the weight of the car, faster and the engine works harder to overcome wind resistance.
OF course if you want to get serious about saving money and can do so, ditch the car and buy a bicycle. The gas stations will shake their fists at you while you become healthier.
Another way to get better mileage is to buy a car with continuously variable transmission (CVT). This transmission keeps the engine at it’s most fuel efficient RPM, and varies the gear ratio in order to accelerate (although there aren’t actual gears in a CVT).
“So if the RPM theory is true, then my 1 ton Civic at 3,000 RPMs at 65mph is less efficient than my 2.5 Ton F150 at 1500 RPMs at 65mph. That’s good to know!”
I think the “RPM theory” being referred to is talking about the gas millage relative to a single vehicle. Ergo, your Civic will use less gas at 1500 RPMs than at 3000 RPMs.
I guess you didn’t learn much about relativity in physics?
I live in South Florida, where you need the A/C year round. I just spent six months with no A/C in the car (busted compressor clutch), and therefore drove around with the windows down. My average MPG went from 24 to 26 up to 27 to 30. Once the A/C was repaired, it dropped right back down. I figured I saved enough on gas over the six months to pay for the repair…
@ToyotaTs
Funny, I have been driving a 2006 toyota prius for just about a year now and have kept an accurate record (computed, not reported by vehicle) of fuel consumption and I find the opposite is true. When I drive long winding back roads where I can maintain a constant speed of around 35-50 MPH I get between 50-60 MPG. When I do lots of local driving, stop and go, I get as low as 40. I find the biggest factor on fuel efficiency with the Prius is outside temperature. I average 55 MPG in warm weather (50-80 F) and 45 MPG in cold.
my bicycle seems to get NAN miles per gallon. but it does sometimes take its toll in other ways…
I’ll have you know, I’m burning up the extra fuel all you tree hugger hybrid yuppie pukes are “saving”
Gas prices have nothing to do with supply and demand, they instead have everything to do with political policy and greed.
I drive two cars. One is a 500 horsepower toy, and gets 16mpg around town (~24 on the freeway). The other is a 425 horsepower land barge, and it also gets around 16mpg (20 on the freeway). That yuppie hybrid group can kiss my ass, stay in the right lane and let me pass
@32
Not to mention the insane amount of pollution required to create the batteries in the Prius.
Prius are not good for the environment, they do get some pretty good fuel economy but you would need to drive it for 15 years before that small increase in fuel economy is going to offset what you created buy having the battery manufactured.
Fuel economy isn’t everything.
You can save $ by putting regular in your Civic, Explororer, Audi, etc. Save the ULTRA and Super grade gas for the H2′s, Vipers, and Haulers.
You can also leave your car running with the windows down and doors unlocked while you spend 20 minutes in the grocery store
I wonder how much of the country’s fuel is being wasted in traffic jams and worker’s air conditioning
Contact your local delegate to widen highways and add Red light sensors to change lights, that’ll save $
Mythbusters did tests on the AC vs. open windows and at 50 MPH the Ac lost.
It’s been eluded to, & that math formula is still giving me a head ache, but ‘pushing the air’ in front of your car is the greatest cost of running your car beyond, even considering peak performance at a certain rpm.
think about it.
2000 rpms at 20 miles per hour = less effort for your car than
2000 rpms at 60 miles per hour.
When your car is traveling at constant velocity, the net force on it must be zero. (when your car is standing still, the engine isn’t forcing it to move forward and the air isn’t forcing it to move backward) Since it needs a forward force from the ground (your engine attached to the tires), something must be exerting a backward force on it. On a level road, that something can only be air resistance.
if you want to see what your car has to put up with try sticking your hand out the window at both speeds & see if you can ‘feel’ what your cars engine is putting up with.
That said, 60 mph, should always yeild better MPG than 80.
this is also why your car has a ‘top speed.’ eventually, the motor doesn’t have enough power to overcome the amount of air resistance (backward force). ie: your engine’s ability to accelerate is = to the air resistance coming at it.
I’ve heard the ‘formula’ described this way:
the ‘force’ of the air on your car doubles exponentially as you accellerate.
here’s an example of the backward force of the air (in pounds) against a corvette at various speeds.
You can easily see that
(mph) 15 30 60 90 120 150
Force 3.60 14.5 58.0 130 232 362
(the ‘force’ can also be looked at as a measurement of how much more ‘air resistance’ there is at each of the speeds.)
of course you need to have properly inflated tires, and a well maintained engine, but you can clearly see here, that as you increase speed, you severly increase in effort that the engine must exert. The only way your car exerts more effort, is by using more gas!
Engines are most efficient steady-state at their torque peak, where BSFC (brake specific fuel consumption) is at it’s lowest. Match the torque peak of an engine to a vehicle’s most used cruise speed via proper gearing, and you have an optimized combination. The single variable with the greatest effect on fuel economy is your right foot– the greater the throttle opening, the more air will flow into the engine, and a commensurate amount of fuel will need to be mixed to insure proper combustion and the longevity of the engine.
As far as air drag and the 45 mph magic number are concerned, it’s a ‘sweet spot’ where most vehicles experience considerably less drag than at higher speeds, and so require little power (hence fuel) to travel. Test it yourself… stick your hand out the window at 45mph and hold it in place. Try again at 55, 65, and 75 mph. The force required for you to hold your hand in place correlates to the amount of force required for your vehicle to push it’s way through the air.
@cptvitamin (37)
Yes, your driving in the 30mph and lower range definately puts you in the range to be utilizing the electric power more…especially if you accelerate fairly slowly.
Our commute is always 45mpg or so, so we end up getting about 45 to 50 mpg depending how much stop-n-go and 25mph (or is it 23mph the cutoff?) or less traffic we get. We did notice a few mpg drop with the cold weather too…which from what I have read is about the same for most cars.
@Loe III (40)
One of the universities did a study of the Prius emissions and said it was very, very environmentally friendly so that probably easily offsets any battery making process and disposal. There’s pollution from petroleum product manufacture too, no? Even with the by-product down-level chain…
Tt
@Brains (39):
“politcal policy and greed”
Agree for the most part. Would rather reward Toyota with a few purchases of vehicles utilizing technology heading in the right direction than reward big oil, it cronies, and OPEC and crew.
Just cut us puny vehicles some slack in your humongous and power oriented vehicles, okay?
Tt
My car doesn’t use any gas! (It’s a VW Jetta diesel.) I’m averaging about 34MPG mixed driving. Now that diesel prices are lower than regular gas, it’s win-win. The only down-side is the oil changes are more expensive because it requires a special VW-approved synthetic grade.
The A/C vs. wind drag one is typically not true, although it probably would be true for certain car designs where the windows are huge scoops, T-tops, and some convertibles (mostly where air doesn’t flow past the window instead of into it). The reality is that A/C becomes more efficient the faster you go (as more airflow increases it’s radiant cooling capacity) and drag increases at velocity-squared (so doubling your velocity quadruples your drag), but drag is very low in comparison to A/C drain to begin with. Another way to look at this foundation is: if you were sitting still, is A/C or open windows more fuel-efficient? Clearly open windows.
What this all means is that there is a point where the A/C efficiency increasing crosses the line corresponding to drag (or speed efficiency) decreases, and it becomes better to use the A/C. For most cars, though, this point is probably way beyond the speed limit.
My Volvo has a readout that shows me the MPG updated every couple of seconds, and I have tested A/C vs. open windows in a variety of conditions, and open windows universally wins, even at 70+ mph. I am my own Mythbuster…
I don’t really car about this whole gas thing since there is no real way to avoid it. I would like to say that one of “Rob’s” posts was absolutely perfect. I wish more people would learn to simply take their foot off the accelerator instead of constantly braking all the time. Unless there is a reason to come to a sudden or complete stop or reduce your speed drastically, you really shouldn’t need to use your brakes that much. I hate people who constantly tap on their brakes while they are driving. People need to learn to drive with the cars engine not with its brakes.
The Mythbusters guys should never be cited as an authority on anything. What they do on their show is ‘entertainment science’.
(i do enjoy the show but their conclusions should never be taken seriously)