• Oct 29, 2009
Over the last few decades, the average weight of a vehicle sold in the U.S. climbed steadily after we got over the oil embargoes of the 1970s. Today, though, auto companies are putting a lot of effort into reducing weight – Lotus set up an entire lightweight structures division, BMW is investing millions into carbon fiber and Jaguar loves aluminum – because every ounce you take out of a car improves the vehicle's performance and fuel economy. Options for weight savings that automakers are investigating include installing things like plastic fuel tanks (PDF) and using carbon fiber instead of steel. As we discovered in a previous Greenlings, carbon fiber is a remarkable, lightweight substance that will likely not be used widely until prices come way, way down.

Today, one of the main reasons automakers want to reduce weight is because it's a great way to increase MPG numbers. AutoblogGreen reader GenWaylaid sent in a Greenlings question about how, exactly, reducing weight helps efficiency. We investigate his query after the jump.

Let's start with the easy and simple numbers. The EPA says that for every 100 pounds taken out of the vehicle, the fuel economy is increased by 1-2 percent. Based on a gallon of gasoline costing $2.58, this translates to savings of between $0.03-$0.05 a gallon. Of course, 100 lbs. in a small hatchback is going to make a bigger difference than those same 100 lbs. in a Tahoe, so make reasonable assumptions about what going lightweight can offer you.

For a more detailed look at what's possible, we turn to a report issued by the Aluminum Association, Inc. based on research by Ricardo. The chart below show that for a small car with a 1.6-liter engine, reducing weight by five percent led to an increase in fuel economy of 2.1 percent on the EPA combined rating. Eliminating 10 percent of the weight gave a 4.1 percent mileage boost and a dramatic 20 percent weight decrease improved fuel economy by 8.4 percent. To find out how other vehicle types fared, download the PDF. (See page 35 of the report for a great chart showing the effect of 100-lb. reductions on different vehicle types in different situations).

To download the full PDF report, click here.


Ways to remove weight in your own car

Since the automakers have already made their decisions regarding how heavy your vehicle is going to be, it's up to each driver to eliminate weight whenever and wherever possible. The place to start is in the trunk and in the back seat. Got some old boxes in there you never use? Put 'em in the garage. Been carrying around a set of golf clubs since last weekend? Put 'em aside for now. Got a dead body in there? Um, that's an entirely different set of problems.

Once the obvious detritus is removed, there are a few other ways to lighten the load. While we have to admit that losing a bit of belly fat can technically make a difference and is probably a healthy choice, we don't want to put too much emphasis on that angle – it's been called out already. People who know what they're doing (and by this, we mean they have a reliable back-up plan, either a cell phone and time to wait or AAA or something) sometimes ditch the spare tire and just deal with it when a tire goes flat.

An extreme example of a way to driver around with less weight would be to only fill up the tank half way. Sure, you're trading time for efficiency, but if you live near a gas station and don't drive too often, this could be a reasonable thing to consider. Gasoline weighs about 6 pounds per gallon and diesel about 7, after all. Filling up to just half of a ten-gallon gasoline tank means you're taking 30 lbs. out of the car. Consider it.


The weight of the future

One of the rarely discussed realities of the U.S. auto industry is that even as fuel economy ratings for most vehicle classes stayed about the same for the past few decades, the vehicle themselves have gotten heavier with all of the added entertainment, comfort and safety features. These numbers were able to diverge like this because engineers were making the vehicles more efficient in ways that didn't involve saving weight. Now that the industry is focusing on shedding pounds – something that will become even more important once heavy automotive batteries for plug-in vehicles start appearing more and more often – the gains made with heavy cars can be applied to lighter vehicle. After all, U.S. cars still have a long way to go to reduce weight, and we'll all reap the benefits thanks to reduced fuel usage.



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  • 34 Comments
      • 5 Years Ago
      I've been handing the weight problem a different way. For every pound I gain, I pay an Ethiopian to lose a pound for me.

      I call it weight offsets.

      I have no guilt and the planet is better for it.
      • 5 Years Ago
      for the record...

      I am a long time believer in reducing the weight of my car. I have a BMW e36 sans 200lb and i must admit, i get better fuel economy in city driving but it has not helped highway driving. There is a notable increase in acceleration and braking distance which is the most fun part about it.

      Yes, cars have been getting more heavy, this is due to safety regulations. They have made up for this by introducing new engine technologies like variable valve timing and direct injection. One cannot fathom how efficient a 2000lb car with a high tech engine in it would be. I drool at the thought of a Honda CRX with a r18a civic motor, which is basically like taking a civic and chopping 600lbs out of it.

      But again, weight really helps city gas mileage more than anything, highway not so much ( unless it's hilly ). When something is rolling and has momentum, it's all about unsprung weight, rolling resistance and aerodynamics.

      I'm all for weight reduction as long as it's sane. I've got my spare tire out, a mechanical fan delete, lightweight rims, no headliner, no AC ( don't need it where i live ), and lightweight seats in my car. One could take this further.. just don't go off the deep end.. lol.
      • 5 Years Ago
      Seriously? You have to ask? I have a simple answer.

      One word:

      Physics.

      Take it, learn it, love it and hate at the same time.
      • 5 Years Ago
      There is a lot more to be gained than just fuel economy... Brakes, tires, etc.... But the car will coast less - even in neutral... So sometimes the gain is not always applicable to practical day to day driving...

      Light is right said Lotus founder Colin Chapman.

      Too bad most people have no idea how leaden their right foot is!
      • 5 Years Ago
      Well only running with a half of a tank of gas may make sense from a weight perspective, but my car--for whatever reason--typically pulls 250-300 miles on the first half tank, and then maybe a 100 on the last half tank.
        • 5 Years Ago
        you are filling your gas tank beyond what the meter is reading as full. Full is measured as near the top of the tank, but additional fuel fills the top of the tank and the tube leading to the tank- beyond what your fuel gauge measures. There also tends to be a little margin of error built in at the bottom of the tank so that people do not run out of gas... so unless you run it to full empty, you really do not know what is going on there either.

        Despite what your gas meter is reading, you do not get better fuel efficiency with a full tank.
        • 5 Years Ago
        Doctor_D: Fill the tank by volume and not by the indicated halfway point. Eg if you typically fill 14 gallons from near empty, fill 7 gallons when you hit your usual near empty point.

        However, filling half a tank is a good example of premature optimization. Your fuel economy might improve by 0.2 - 0.5%. That fuel economy increase will quickly be destroyed when you have to make an additional trip to the gas station per full-tank. Even if you stop and fill up while out running errands, you will burn enough fuel to erase your fuel savings. 0.2 - 0.5% would give you an extra 0.8 - 2 miles on a 400 mile tank, less considering the maneuvering and startup costs of making an extra pass through a filling station.
        • 5 Years Ago
        Doctor_D, My car does that too! I figure if i fill my car up always at the 1/2 tank line, I'll probably double or triple my mileage. Works every time.
      • 5 Years Ago
      Wow, didn't read all the comments...but we are clearly split into two parties...and we're screwed. A small percentage of the population still understands, math, physics and reality.
      The other half hug themselves and lament the death of the electric car and the 100 mpg. carburetor at the hands of an evil government...who are both complete idiots and, yet, capable of vast conspiracy.
      JH


      • 5 Years Ago
      whats wrong with socialism, I love communism
        • 5 Years Ago
        Hundreds of thousands of dead Falun Gong and mountains of frozen Gulag workers in Siberia think your statement is moronic. I tend to agree with them.
      • 5 Years Ago
      Awesome article. Thanks for the interesting information.
      • 5 Years Ago
      This article is ridiculous.

      The numbers in the first paragraph seem reasonable. But reducing the weight of a car by 10% is completely unrealistic - that's 250 lb reduction for a 2500 lb car. It's pretty unlikely that you have even 60 lb of unnecessary weight; removing 60 lb would improve the fuel economy by less than 1%.

      The correct conclusion is: "Carrying a bit of extra weight does NOT noticeably reduce the fuel efficiency. It's just silly to follow that with tips for removing extra weight from a car, like filling the tank halfway (maybe 30 lb weight reduction). There are FAR easier ways to save gas, like combining multiple trips into one, reducing highway speed by a few mph, etc.

      And for what it's worth, I used to have a Dodge minivan; this vehicle DID have a lot of removable weight, namely the middle and rear seats. I couldn't detect ANY change with the "divide the trip odometer reading by the amount of gas I just bought to fill it up" method.
        • 5 Years Ago
        @Nateb123
        Yup, unnecessary height, mostly in tall fat ugly SUVs, is the worst car design choice imaginable.

        Bigger frontal area -> increased drag, higher center of gravity -> worse handling, increased weight, and it blocks the view of other drivers. More space under the car is also probably bad for airflow and aerodynamics. Agghh!
        • 5 Years Ago
        KK,

        I'm pretty sure the Ricardo numbers are more for automakers, where removing 250 lbs. is feasible (not easy, but possible), and not for drivers.
        • 5 Years Ago
        I concur. Reading the details of the test results really does lead to the conclusion that all those little weight saving tips really are inconsequential. For instance, filling your tank half way means that you will probably spend more fuel going to the gas station twice as often. There will always be someone who says "every little bit helps", but when you start looking at the indirect results of the petty little tips, the driver is probably wasting more fuel, time, and energy.

        The greatest way to save energy and fuel is for that to be engineered into the vehicle and then buying the most efficient vehicle that serves your purpose. Manufacturers such as Honda with its consistently larger and thirstier Accord are headed in exactly the wrong direction. Now I wouldn't buy an Accord, not just because of its lower efficiency relative to the competition, but because it has become bigger and more bloated than what I care to drive.

        • 5 Years Ago
        Well, if car makers actually figure out how to make a lower car that meets crash standards again, 10% weight savings should be easy pickings. Look at a Honda Accord from the late 80s. It's not hugely roomy but even if it were longer it would still be quite light. This is more than partially due to the fact that cars now are insanely tall to provide a nearly upright driving position. Just look something as "compact" as a Toyota Matrix for comparison and where all the weight comes from becomes apparent.

        It's unnecessary height. If you want a high ride or lots of hauling space, a sedan or hatch is not your segment of interest anyways. Yeah the car will do better in a crash against a big truck or SUV but pedestrians will obviously experience more fatalities as a result. The real reason these cars are so big is people's thinking is broken logic and mindless fear. People have a knee jerk reaction to get a "safer", bigger car ignoring that others will inevitably follow suit and get a big car as well. Suddenly they've made the situation worse because the two vehicles crashing have worse braking, handling and visibility (which likely contributed to the crash's severity and likeliness of it happening at all) and now they are colliding with WAY more momentum.

        If people got their heads out of their butts they'd realize we share the roads with buses and trucks, and that regardless of whether you hit them with your Tahoe or your Miata, you're pretty much screwed. Might as well reduce the damage (and cost, because this weight issue is all about fuel efficiency as well) to both parties by having a bunch of small, low cars on the road.
        • 5 Years Ago
        KK, that's wrong in the extreme. a comfortable very fast 4 seater car can be made to weigh less than 500kg.

        you're thinking like a ricer, removing rear seats and changing the hood to a carbon fiber one. amusing : )
        you don't modify a car like that, you redo it in materials that are many times stronger and lighter than the soft heavy steel cars use today. glass fiber can have 10 times higher tensile strength and weighs only 1/3 of steel. that's a 30 time improvement over steel by weight. granted that's only tensile strength but still.

        fiber glass is more or less as strong as carbon fiber and weighs the same. that's why its used in for instance glider aircraft. glass is also relatively cheap.
        a sleek car made in fiber glass can be very light and extremely efficient. a few has been demonstrated in the past. loremo is trying something like that now and so is aptera with matching improvement in efficiency.

        the reason this has not been done in the past in large scale is because evil mindless people rule the world.

        The acceleration performance of the Tesla Roadster is only the beginning of what is possible with intelligent design. Get with the program
      • 5 Years Ago
      Interesting read. We have a bunch of users over at www.fuelmileage.com tracking their MPG's. It would be interesting to see the effect if we asked all the users to remove excess weight and see how much the MPG's improved over the course of a month.

      • 5 Years Ago
      Run Synthetic oil in all the sumps.
      Check the tires for proper inflation.
      Preform regular maintenance as scheduled.
      Check tire alignment and suspension components for proper operation.
      Drive smoothly and avoid driving under emotional duress.
      Do all errands at one time and walk or ride a bike for those impulse errands.
      Buy stuff made and grown locally and You are supporting You friends and Neighbors
      and keeping Your money away from terrorist's,socialist's and the corporate asshats.
      Being green never felt so good or healthy.
        • 5 Years Ago
        Nozferat,
        You imply that I am blaming all Socialists and a few religious zealots for My own lifestyle.
        My lifestyle is My responsibility and I tend to it daily by working to buy things for survival and to help others.
        I could live a more opulent life but I choose not to.
        I've been there and I know that it doesn't bring happiness,so now I serve others in My community.
        In My role as a Civil Servant,I make roughly one third of the income that is available to those in the private sector.
        I have no grudge against those People,much like Myself,Who are struggling to survive,.
        I do have issue with People who feel it is Their right to dictate the terms of that survival for profit and Their own em-betterment.
        I am sorry,but Socialists are property of the state and I fear that given half of a chance the People at the top here in America would love to put themselves in that position of Ownership
        over the rest of the World.(see Manifest Destiny)
        The way to get rid of a pest is to make it get its food elsewhere and what I propose is simple:
        Reduce,Re-use,Recycle and live within Your means.

        What this World does not need is another fatwa or intifada,what it does need is a level playing field for the People when it comes to acquiring the basics for life and then perhaps there won't be such a need for religion or greed or power,having first defeated thirst and hunger and fear and ignorance.
        No form of Government has successfully addressed these issues,so it falls to each of Us.

        • 5 Years Ago
        How to reap the benefits of green motoring, if you're not motoring at all ;-) It does make a lot of sense, your approach. Pity the marketing fluf seems to push us in a different direction. EV crisis next?
        • 5 Years Ago
        You seem to have a very self-centered, self-revolving, egocentric view on things...perhaps that's your problem. What you do affects everyone else....however little it may seem to you. So your lifestyle IS other peoples' problems somewhere down the road.

        • 5 Years Ago
        Awwwh ...... Nateb 123 you are so mean to hippies.

        Looks like you need a little love and some space to grow up.

        • 5 Years Ago
        RAIN:

        You're blaming socialists and terrorists for your greedy self-indulgent lifestyle? Hmmmm...I wonder how that works.
        • 5 Years Ago
        NATEB:

        I wonder who's the bigger pretentious douche actually...a hippie who actually gives a crap about their surroundings and doesn't their lives run by corporations or someone like you who believes that corporations should keep going with their waste, rampant pillaging, and the destruction of the same environment you so undeservedly use everyday to keep your pathetic self alive.

        Hmmm?? Which do you think is more pretentious?
        • 5 Years Ago
        Buying locally does more then prevent all that political B.S., it helps the environment and your body as well. When I moved to Florida from South Carolina, I had REAL bad allergies. One of my friends suggested the old wives tale of eating only local honey, and eating atleast a Tablespoon a day for the first week. It's said that since the honey is made from the local flowers, and thus has local pollen in it, it helps your body get used to the surroundings faster then doing nothing. Along with buying that local honey, buy the rest of your fresh products and cut down on gas used by shipping companies.
        • 5 Years Ago
        Well Ma'am, it seems like you've got a pretty serious hippy infestation here. A full-blown drum circle in the yard is no laughing matter...

        Seriously, come on. This is a topic on engineering and you hippies are talking about buying local produce? Stop spewing your own anti-corporate, pseudo-naturalistic dogma to anyone who will listen. It's obvious you all just need a little pat on the head from each other because you know deep down you're hugely pretentious losers.

        Plus if you were going to comment on driving economically properly, you would have included using engine braking. Stupid hippies.
      dzspleen
      • 5 Years Ago
      "Based on a gallon of gasoline costing $2.58, this translates to savings of between $0.03-$0.05 a gallon."

      You might want to double-check your math there. Losing weight doesn't make gas less expensive, it lets you drive a longer distance with a given amount of gas.
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