We Test the Tips

What Really Saves Gas? And How Much?


  • 2005 Volvo S40 and 2005 BMW X3

    2005 Volvo S40 and 2005 BMW X3

    Both the 2005 Volvo S40 and the 2005 BMW X3 have computerized fuel gauges which allowed us to study how gas mileage varies under different conditions. | March 18, 2010

3 Photos

With gas prices so high, the media is awash with lists of gas-saving tips. Well how's this for a tip? If you listen to us, you can see hybrid-type savings without having to buy a new car.

By changing your driving habits you can improve fuel economy up to 37 percent right away (depending on how you drive). Combine several tips and perform routine maintenance and you will save real dollars, not just pennies.

A miracle? All we did was take several of the most common tips out there and put them to the test over a remote 55-mile route in the high desert of California. Some of them worked like a charm. Some of them didn't work at all. We'll give you the breakdown.

These tests were done under real-world conditions — not in a government lab somewhere. Our results can be matched by anyone — even you.

The wonderful part about what we found is that improving your car's mileage is just a matter of changing your habits. Stack a few of these winners together and we'll bet that you'll see a substantial savings at the pump — without the need for a new car.

Test #1 Aggressive Driving vs. Moderate Driving

Result: Major savings potential

The Cold Hard Facts: Up to 37 percent savings, average savings of 31 percent

Recommendation: Stop driving like a maniac.

Aggressive vs. Moderate Driving: read the entire test

Test #2 Lower Speeds Saves Gas

Result: Substantial savings on a long trip

Cold Hard Facts: Up to 14 percent savings, average savings of 12 percent

Recommendation: Drive the speed limit.

Lower Speeds Saves Gas: Read the entire test

Test #3 Use Cruise Control

Result: Surprisingly effective way to save gas

Cold Hard Facts: Up to 14-percent savings, average savings of 7 percent

Recommendation: If you've got it, use it.

Cruise Control: Read the entire test

Test #4 A/C On, Windows Up vs. A/C Off, Windows Down

Result: Nice in theory; not true in practice

Cold Hard Facts: No measurable difference (unless you open the sunroof, too!)

Recommendation: Please, make yourself comfortable.

Air Conditioner: Read the entire test

Test #5 Check Your Tire Pressure

Result: Important for safety and to reduce tire wear

Cold Hard Facts: No measurable effect on the vehicles we tested

Recommendation: Check your tire pressure often but don't expect a big savings.

Tire pressure: Read the entire test

Test #6 Avoid Excessive Idling

Result: More important than we assumed

Cold Hard Facts: Avoiding excessive idling can save up to 19 percent

Recommendation: Stopping longer than a minute? Shut 'er down.

Excessive idling: Read the entire test

The Tests

Our results are based on two separate fuel testing sessions. On each occasion we took two cars from the Edmunds.com long-term fleet and drove on a 56-mile test loop. Our route circled Owens Lake near Lone Pine, California, at the foot of Mount Whitney, the tallest mountain in the lower 48 states. We chose the route because it was so deserted we could vary our speed and driving style without interfering with the flow of traffic. The only other cars we saw on the route were a caravan of test vehicles from Mercedes-Benz. We drove the loops back-to-back to ensure that we were comparing similar wind and temperatures. We logged our results and later put them on a spreadsheet where the results were averaged.

Test #1: Aggressive vs. Moderate Driving

This is gonna hurt. Our tests showed that the most significant way to save gas is: you. And we're talking massive fuel economy gains. Think you need a hybrid? Chances are you've got hybrid-style mileage in your gas pedal foot. Don't mash the gas when you start up. Take the long view of the road and brake easy. This tip alone can save you unbelievable amounts of gas. If you slowed your 0-to-60-mph acceleration time down from your current 10 seconds to a more normal city pace of 15 seconds, you'll feel the savings immediately.

Method: We conducted this test four times. The first time we did the full 55-mile loop once by accelerating aggressively 15 times at 3/4-throttle from zero to a cruising speed of 75 mph. We also applied the brakes hard to come to a full stop. Then, we drove the second loop by accelerating moderately 15 times at 1/4-throttle to a cruising speed of 70 mph. We braked lightly to a full stop. In the second set of tests we drove 25 miles making 25 rapid accelerations to 65 mph at 3/4-throttle. After 1 minute of cruising we braked hard and repeated the cycle up to 65 mph. We then drove the same distance making 25 moderation accelerations to 60 mph at 1/4-throttle. After 1 minute of cruising we applied the brakes easily and came to a full stop.

Test #2 Lower Speeds Saves Gas

Remember a thing called the speed limit? On most highways it is either 65 or 70 mph. How fast are the cars and trucks around you going? From 75 mph to 90 mph. These people are wasting a lot of gas for the chance to get there a little earlier. Factor in safety concerns and a speeding ticket once or twice a year and going fast is a costly proposition.

Method: This test was simple. For 50 miles we drove with the cruise control set at 65 mph. Then, for another 50-mile stretch we drove with cruise set at 75 mph. We repeated this test going in the opposite direction. It is amazing how obvious the difference in gas mileage was. Just think what would have happened if we had slowed down to 60 mph. The only problem is with impatient drivers behind you. One driver became so irate that he tried to run our editor off the road. Still, if you are pinched by gas prices. Leave a little early and drive the speed limit (in the slow lane).

Test #3 Use Cruise Control

Using cruise control is a bit of gas-saving advice frequently on tips lists. We have always agreed with this tip in theory but we hadn't expected such significant results. First, it smoothes out the driver's accelerator input by preventing nervous "surging." Second, it makes the driver take the long view of the road rather than reacting to every change in the traffic around them.

Method: We did this test twice with four different cars each time driving the 55-mile loop. The first time we set cruise control to 70 mph. The second time, with the cruise control off, we varied our speed between 65 mph and 75 mph. We tried to mimic the driving style of a person who is in moderate freeway traffic.

One thing that's important to note: if you are in a mountainous area you should turn off cruise. It will try to keep you up to the speed you've set and will use a lot of extra gas downshifting to lower gears to accomplish this.

Test #4 A/C On, Windows Up vs. A/C Off, Windows Down

This has got to take you back to the days with the family on vacation. Dad says, "Turn the A/C off! It wastes gas!" And Mom says, "We can't roll the windows down or everyone on the highway will think we can't afford A/C." And you're in the back roasting, hoping someone will win the argument so you can cool off.

Well, family psychology aside, if dads are still saying this, they aren't necessarily right. While the A/C compressor does pull power from the engine wasting some gas, the effect appears to be fairly minimal in modern cars. And putting the windows down tends to increase drag on most cars, canceling out any measurable gain from turning the A/C off. But this one depends on the model you're driving. When we opened the sunroof in our SUV, the mileage did decrease even with the A/C off. Still, in our experience, it's not worth the argument because you won't save a lot of gas either way. So just do what's comfortable.

Method: We drove the full 55 mile-loop in two cars at equal speeds both times — 65 mph. The first loop we drove with the A/C on and the windows up. The second loop we drove with the A/C off and windows down. In the second test we drove 20-mile loops. This was far enough to see our gas mileage level off and remain steady on the computer trip meter.

Test #5: Check Your Tire Pressure

No matter how many times drivers hear about the importance of tire pressure, most of them don't do anything about it. They probably don't like squatting beside their car in a busy gas station with fumes swirling around them. But is it important? The answer is yes, for a number of reasons. Properly inflated tires are less likely to fail at high speeds. They wear more evenly and, yes, they deliver better gas mileage. How much? In this test we saw a modest difference in two of the cars. It might have been more dramatic with different tires on different cars. Experts swear by it; we couldn't really document it. And we wound up wondering if tire technology, like the design in other areas of the car, had improved.

Eventually, we concluded that each set of tires is different and every vehicle is different. We recommend that you do your own tests to see what inflation setting gives you the best fuel economy.

Method: We drove the 55-mile test loop four times at 60 mph — twice with tires at or above proper inflation. Once, we did the test with the tires 5 psi below the pressure recommended by the manufacturer. Since this produced very little difference we enlarged the gap and under inflated the tires by 8 psi. We felt that it was important to make sure the tires were inflated to the recommended level or above.

Test #6 Avoid Excessive Idling

If you turn off a light bulb as you leave the room you'll save electricity. If you turn off your car you will save gas. Obviously. But related questions are more difficult to answer. If you're only stopping for only a minute, is it better to shut off the engine or keep it idling? Should I shut off the engine in traffic? How much gas will this save? What rule of thumb do I use when trying to save gas this way?

Method: We took two cars and drove a 10-mile route stopping 10 times for two minutes. We shut down the car each time. Then we drove the same route at the same speed and let the car idle for two minutes.

Conclusions

The good news is that you can drastically improve your gas mileage. The caveat is that you have to change your driving habits. If you are willing to change, you'll find many related benefits too: no speeding tickets, greater safety, reduced stress and lower repair bills for tires and brake pads. In the long run this will save you money. And who knows? You might like the new you.

Comments

  • urebelscum urebelscum Posts:

    Found this page while looking for ways to increase gas mileage, with the cost of gas going up again. Some bad testing in there, mixed in with good. Thank you for posting the methods used. If you repeat any of them, could you make the following changes? (Some are very hard, or very numerous, to do though.) Test # 1: Please don't mix changing the braking with the acceleration. Which part affected the results more? No way to tell with the way you tested it. Might have to run it as two separate tests, as brake/accel combinations can multiply very quickly. Test # 2: Great test: same path, both directions. Could you test other speeds? One old study ( table form: http://cta.ornl.gov/data/tedb29/Edition29_Chapter04.pdf page 4-31, or graph form: http://en.wikipedia.org/wiki/File:Fuel_economy_vs_speed_1997.png ) shows speed matters, but three of the nine tested cars got better mpg at 60 than 50, and one car got better mpg at 65 than 55. However, those cars are now over at least 13 years old, and new cars might have shifted their peaks. Testing as many cars at as many speeds would be very time consuming, but testing an SUV, hybrid, and either a sedan or coupe should be enough for a general idea if you run it again. Test # 3: How much did you vary between 65 & 75 not in cruise control? Any braking? How heavy was the acceleration? Could you test CC on hills and mountains to back up your statement on not using CC in mountains? How hilly/mountainous does it need to be for CC to be worse? How much worse is it than "normal" no CC driving? Test # 4: What about AC off, windows up? AC on vs AC off is asked far more often than the two you tested: comparing the three would be the best. Also, what speeds was the second (20 mile loop) set run at, and if different, did the speeds make a difference? If not different, could you test different speeds? What about testing AC high (or 65 for auto) vs AC low (or 75 for auto) also? How about a low HP car vs the medium-high HP cars you tested? Test # 5: Great test, and great you deflated even more when it first didn't make a difference. Test # 6: Good test. Just a wording question. Was the 2 minutes the total for the 10 miles, or for each stop? It sounds like each for the turn off motor, but like a total for the leave in idle. I'm most interested in tests #1 and 2, greatly, and a little on test #4 since my car has auto climate control, and I have less direct control of AC than I used to. Thanks for doing the tests in the first place. I hope you spend the time and effort to redo some of them, with an expanded range of cars and improved testing methods.

  • bigredrasa bigredrasa Posts:

    Two points: 1. I drove a convertible with top down & AC off, then with top up and AC on. Top up netted noticeably better MPG. 2. Excessive use of the stater can cause premature wear. How much? I don't know. I do know some starters are expensive to purchase and replace. A failed starter on a clod winter night, in the middle of nowhere, is not worth an MPG or two.

  • dvdny dvdny Posts:

    Decent article, with one exception. For test #1, using my Prius's built-in telemtry, it proves that slow acceleration is a fallacy, and it's better to quickly accelerate (not floor) to cruising speed and then stay there The reason being most of your fuel is used during acceleration, and whether you accelerate slowly (35mpg for prius) or quickly (25mpg), the worst you can possibly do is get 20mpg (prius), whereas the sooner you can get up to cruising speed, you can get conceivably get infinite mpg during the saved not accelerating slowly. I've tried the 'egg under foot' method of 20-second acceleration in the prius, and I get ~5 MPG less on a tank. The Prius teaches you that it's all about cruising, and if your car has an instantaneous MPG gauge, you too will see the same results in your car. Try it!

  • dvdny dvdny Posts:

    Good point, 'urebelscum'. What they did also not include was the #1 rule of gas waste: 'Braking = wasted gas', plain and simple.

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